Refinishing: Who has tried a shortcut?
Ian Forbes
There has been quite a bit on refinishing on RAS recently. Most people
advocate that when gel-coat starts cracking up, it is essential to remove
it ALL.
Does anybody out their own a ship which was refinished without removing all
the gel-coat? What is the service history of these gliders?
If the RAS collective are right on this, I suspect that there will be a
number of hard luck stories out there from people who have discovered this
the hard way.
Personally, I know of many ships that have been resprayed. I suspect many of
them were not sanded down to glass and those that I see around don't look
too shabby. I can't help feeling that there is another side to this story.
I used to own a share in Nimbus II that was resprayed with poly urethane
paint (Glasflurit "Durothane K" they claimed) by the previous owner. I
don't know what condition the gel was prior to painting, or how much gel
was removed. There was no obvious sign of a primer layer under the paint
either.
However, I had it for 10 years and the poly finish was perfect when I sold.
The only problem we had with it was doing minor repairs. It was very
difficult to re-spray a small area without a visible brownish "water mark"
where the new and old paint met. But we just lived with a few water marks.
We used to polish the finish with a "liquid polymer" car polish. (Why not,
car polish on car paint, works on hundreds of thousands of cars ..) Can't
say we had a problems from that, except that I suspect it may be have had
something to do with the water marks.
For small dings we filled with body filler and/or high build poly urethane
primer, then resprayed with aerosol lacker. After sanding and polishing,
the results were pretty neat. For bigger repairs we masked off and
resprayed an entire "panel" with the original poly urethane, primer and top
coat.
After my experiences I would never pay anybody to refinish a glider with gel
coat. If I ever bought a new glider, and I had a choice, I would order a
urethane finish.
Now I have bought a share in an LS3a that has the original gel coat finish
over most of the surface. We keep it polished with a "silicon free" glazing
wax. But it is pretty cracked up and I am wondering how it is going to
become a urethane finish.
Who has been down this road before and tried a "short cut"?
Regards
Ian
Janusz Kesik
Użytkownik Ian Forbes <ifo...@nospam.zsd.co.za> w wiadomooci do grup
dyskusyjnych napisał:g2emrb...@192.168.2.7...
> I used to own a share in Nimbus II that was resprayed with poly
urethane
> paint (Glasflurit "Durothane K" they claimed) by the previous owner. I
> don't know what condition the gel was prior to painting, or how much
gel
> was removed. There was no obvious sign of a primer layer under the
paint
> either.
Maybe it has been painted with polyurethane paint since new? Most of
German gliders some painted with gelcoat as a standard, but I think the
polyurethane paint is an option avaivalble after paying some dollars
more. Almost all (if not all) SZD glass gliders and their late wooden
designs were painted with polyurethatne as a standard fit when leaving
the production hall.
>
> However, I had it for 10 years and the poly finish was perfect when I
sold.
> The only problem we had with it was doing minor repairs. It was very
> difficult to re-spray a small area without a visible brownish "water
mark"
> where the new and old paint met. But we just lived with a few water
marks.
The paint You use, is fresh, new, etc. and the paint layer which has been
laid few years ago is just "old" due to sun, dust, and anything else with
what has it been in contact since painting. :) They're just different
because of age, and even if You have the same paint (the same catalogue
No.) effect most likely will be different in any case.
Regards,
--
Janusz Kesik
janusz.kesik...@gazeta.pl
visit www.leszno.pl - home of the www.css-leszno.it.pl
Ian Forbes
>> I used to own a share in Nimbus II that was resprayed with poly
> Maybe it has been painted with polyurethane paint since new?
No, it was painted by the previous owner. Much of the manual work was done
by his son and his son's friend. I spoke to the friend about this, that is
how I know it was "Durathane K".
>> The only problem we had with it was doing minor repairs. It was very
>> difficult to re-spray a small area without a visible brownish "water
> mark"
>> where the new and old paint met. But we just lived with a few water
> marks.
> The paint You use, is fresh, new, etc. and the paint layer which has been
> laid few years ago is just "old" due to sun, dust, and anything else with
> what has it been in contact since painting. :) They're just different
> because of age, and even if You have the same paint (the same catalogue
> No.) effect most likely will be different in any case.
The effect was cosmetic, and not readily visible, but annoying because no
amount of effort seemed to get rid of it.
I found that sanding the adjacent area with 1200 wet and dry prior to
spraying seemed to help prevent the mark, but it was always there to a
greater or lesser extent.
(Just like cracks in gel coat - they are always present, just the extent
varies!)
Car panel beaters always spray an entire mudguard, door, bonnet etc to avoid
this problem.
Ian
Richard Pfiffner
The only short cut I found was to uses very heavy grit paper to remove the
gel coat. I used 60 grit with a 7" rotary variable speed sander. As I got
close to the fabric I changed to 80 grit. Be carefully you don't sand into
the fabric. I can also recommend that when you profile your wings make sure
you roll or spray on enough surfacer, so you don't have to do it twice. I
also recommend using at least a 3' or 4' long aluminum extrusion to profile
the wings. Use adhesive paper or spray on adhesive. Make sure it is flat.
I intially used 80 grit to profile. The second time I used 200. Then
sprayed DCC acrylic urethane. So far I have 172 hours into the project. But
it finally looks shiney. Estimate about 25 hours left to wet sand polish
and assemble the flaps & ailerons.
Richard
www.craggyaero.com
"Ian Forbes" <ifo...@nospam.zsd.co.za> wrote in message
news:5u0nrb...@192.168.2.7...
Don Johnstone
in two pack acrylic. I was necessary to remove all
the gel coat before this was done and reprofile where
necessary. The gelcoat provided some of the profiling.
It is much easier to maintain than gelcoat and is not
as susceptible to cracking, so far.
I owned a Kestrel previously and we thought about stripping
off the gel and putting acrylic on that. Two reasons
for not doing it, firstly the gelcoat on the Kestrel
was bomb proof and the wings would have needed an awful
lot of profiling work we thought.
Also sanding off gelcoat is not the most health concious
thing you can do.
I have seen gliders which have been re-gelled in Poland
and the cost is about the same as stripping down and
painting with acrylic, it is just a question of durability.
>'Ian Forbes' wrote in message
>news:5u0nrb...@192.168.2.7...
>> Janusz Kesik wrote:
>>
>> >> I used to own a share in Nimbus II that was resprayed
>>>>with poly
>>
>> > Maybe it has been painted with polyurethane paint
>>>since new?
>>
>> No, it was painted by the previous owner. Much of
>>the manual work was done
>> by his son and his son's friend. I spoke to the friend
>>about this, that is
>> how I know it was 'Durathane K'.
>>
>> >> The only problem we had with it was doing minor repairs.
>>>>It was very
>> >> difficult to re-spray a small area without a visible
>>>>brownish 'water
>> > mark'
>> >> where the new and old paint met. But we just lived
>>>>with a few water
>> > marks.
>>
tango4
in acrylic, reseal controls including tape rebate routing, refurbish cockpit
including new carpets and trims and instrument panel respray, repaint
competition and registration marks and numbers. New weight and balance
sheet.
Ian
Ray Lovinggood
Where did you get this quote and what is the contact
e-mail or web site or phone number?
Thanks,
Ray
Brian Case
don't know much about how it was done as it was not done locally. What
I can tell you is that nearly every single one of the old cracks in
the gelcoat are now showing through the new finish. It probably looked
good when it was originally done but apparently didn't last very long.
Brian
Ian Forbes <ifo...@nospam.zsd.co.za> wrote in message news:<g2emrb...@192.168.2.7>...
> Hello All
>
> There has been quite a bit on refinishing on RAS recently. Most people
> advocate that when gel-coat starts cracking up, it is essential to remove
> it ALL.
>
> Does anybody out their own a ship which was refinished without removing all
> the gel-coat? What is the service history of these gliders?
>
> If the RAS collective are right on this, I suspect that there will be a
> number of hard luck stories out there from people who have discovered this
> the hard way.
>
<snip>
W.J. (Bill) Dean (U.K.).
DG Web-site http://www.dgflugzeugbau.de/index-e.html , go to
"Innovations" then under "Comfort:" click on "Polyurethane Paint - The
Better Alternative".
The former owner of your ASW17 has also refinished an LS4 in the same way.
W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.
>
> "Don Johnstone" <REMOVE_TO...@bittering.gioserve.com> wrote in
> message news:brn927$5coc6$1...@ID-49798.news.uni-berlin.de...
>
> A previous owner of my ASW17 refinished the glider
> in two pack acrylic. I was necessary to remove all
> the gel coat before this was done and reprofile where
> necessary. The gelcoat provided some of the profiling.
> It is much easier to maintain than gelcoat and is not
> as susceptible to cracking, so far.
> I owned a Kestrel previously and we thought about stripping
> off the gel and putting acrylic on that. Two reasons
> for not doing it, firstly the gelcoat on the Kestrel
> was bomb proof and the wings would have needed an awful
> lot of profiling work we thought.
> Also sanding off gelcoat is not the most health conscious
Ian Forbes
> We have a Pegasus here that was resprayed over the old gel coat. I
> don't know much about how it was done as it was not done locally. What
> I can tell you is that nearly every single one of the old cracks in
> the gelcoat are now showing through the new finish.
Do you know what was used for the new finish? Is it gel-coat or 2 part
polyurathane paint? If it is paint, what kind of primer went on underneath
it?
Ian
John Ferguson
wings. I did it with Glasurit 2K and high build epoxy
primer.
We took off enough old gelcoat that the surface looked
good, we did not remove all old gelcoat.
We took lots of time removing grease/oil/dirt from
cracks in order that the paint surface would not be
damaged by grease causing the paints not to stick well.
Used lots of degreasing agent, acetone I think.
The epoxy primer took very well and was sanded back
for smoothness then painted with the top coat 2 pack.
I haven't seen it for a couple of years but last time
I did the paint was still holding up and not showing
any signs of crack propagation through the primer and
top coat.
When it was finished, I was very pleased with the results
and the glider flew much better having got back a great
portion of its laminar flow.
The gelcoat, although cracked, was NOT peeling off.
It still was a suitable surface to paint on.
John
Stewart Kissel
crack and propagate to the surface? Also, and I have
googled RAS on this subject, is UV penetrating through
the cracks to the structure harmful? IE, will refinishing
a ship as soon as cracks appear save time and money
in the long run?
JJ Sinclair
there, done that" We probably refinished at least 20 sailplanes. What have I
learned?
1. It's one hell of a lot of work.
2. All cracks, loose material, chips and flakes, MUST be removed. Notice I
didn't say *everything* must be removed. Should everything be removed? In my
opinion, No, it's not necessary. I would say that we removed about 50% of the
gelcoat on the ships we refinished. How have these ships held up? Quite well
with the exception of those ships that were left out all the time (FBO
operations) The gelcoat (Prestec) showed paint failure within 4 years. Cracking
and checking appeared from the outside, NOT cracks that reappeared from the old
gelcoat.
3. I have refinished my Genesis 2 with acrylic urethane (PPG Concept 70) and I
think this is the way to go, especially for ships that will be left out. I
would only use Prestec for spot repairs of gelcoated gliders. By the way, the
*brown ring* around paint repairs is caused by not removing the oxidized old
paint. I recommend the edge of the old paint be lightly sanded with 220 grit
and then control the edge of the new paint, so that the *fether edge* occurs in
the middle of the 220 sanded area.
4. We need some way to get our 20 year old ships refinished for less than
$10,000 US bucks. It just doesn't make good sense to spend any more than that
on an old ship. Some shops will welcome *owner assisted refinishing*. I have
done this. It might well be worth considering taking your vacation at the
local repair shop. The shop doesn't want your project to linger on for months,
but if you offer to work full time for a month, things will move along
satisfactorily. Can you do it at home? Probably not. You need some specialized
equipment, a good air compressor to start with + air boards, spray booth,
respirator, not to mention a cooled, heated and well lighted place to work.
5. Did I mention that it is one hell of a lot of work?
JJ Sinclair
Brian Case
> polyurathane paint? If it is paint, what kind of primer went on underneath
> it?
>
> Ian
It is not a 2 part polyurathane paint. I suspect it is Gel Coat on top
but I can't say for sure.
Brian
B Lacovara
gel coat cracking mechanisms. To address a few of the comments:
1) A gel coat fracture must be removed to the extent of its depth; otherwise
the crack propagation mechanism is in play and will eventually affect the
surface again.
2) A thick and/or flexible secondary coating will delay the re-appearance of
cracks, but not the effects. There must always be concern about an underlying
(but now covered) crack propagating into the laminate.
3) UV penetration of the laminate is a non-issue unless the crack is huge. In
that case the crack itself will be a structural issue.
4) To date, there is not a viable method of "filling" cracks. This is a
function of the inherent surface tension of the potential liquid materials. If
one could fill cracks there is a fair chance two micro-cracks would appear on
each side of the original crack and eventually propagate into larger cracks.
5) To date, no one in the composites industry has come up with a workable
shortcut. A quick fix solution would be worth big bucks, with gliders being a
tiny portion of the overall application.
Hope this helps.
Bob Lacovara
Greg Arnold
have such a problem, while sailboats (which spend most of their time in
the sun and weather) usually have a good gelcoat?
Ian Forbes
I started this thread 4 days ago and I asked:
> There has been quite a bit on refinishing on RAS recently. Most people
> advocate that when gel-coat starts cracking up, it is essential to remove
> it ALL.
There has been lots of advice and theory as to why the above is true. No
doubt it is the recommended approach - recommended by many who are not in a
position where they might have to pay for the work!
However there was little response to my question:
> Does anybody out their own a ship which was refinished without removing
> all the gel-coat? What is the service history of these gliders?
So far there have been two postings of problems with re-finishes. Neither of
these involved a polyurathane finish. Gliders re-finished with extensive or
complete removal of the old gel-coat have held up - at least as well as the
original gel coat.
So I will extend the question. Does anybody anybody know of gliders that
have been refinished with polyurathane and subsequently experienced
problems?
I can answer that by saying I know of one glider that was re-finished with
polyurathane about 10 years ago. There is some localised paint cracking on
the tailplane and rudder which suggests that there were some areas of poor
preparation during the refinish. I suspect that the glass skin on these
areas is thiner more flexible which results in a finish that is more
susceptible to cracking. This was not an "expensive" refinish job, for
example the ailerons and flaps were not removed during the respray. But
overall the glider still looks very neat and I think I can say this finish
has lasted as least as well as many factory gel coat finishes.
Ian
Reuben
Because most sailpanes are waxed throughout the year.
Reuben
Greg Arnold <soa...@REMOVEcox.net> wrote in message news:<BdREb.20434$J77.19108@fed1read07>...
John Galloway
With respect, you cannot establish good practice by
totting up numbers of for and against contributions
to RAS. Bob Lacovara's contribution says it all.
If you come to resell the shortcut refinished glider
will you make clear to potential purchasers that the
condition of the glider laminate is unknown and can
only be checked by removing the new and underlying
old finishes?
John Galloway
At 09:36 20 December 2003, Ian Forbes wrote:
>Time for a round up.
>
>I started this thread 4 days ago and I asked:
>
>> There has been quite a bit on refinishing on RAS recently.
>>Most people
>> advocate that when gel-coat starts cracking up, it
>>is essential to remove
>> it ALL.
>
>There has been lots of advice and theory as to why
>the above is true. No
>doubt it is the recommended approach - recommended
>by many who are not in a
>position where they might have to pay for the work!
>
>However there was little response to my question:
>
>> Does anybody out their own a ship which was refinished
>>without removing
>> all the gel-coat? What is the service history of these
>>gliders?
>
Nolaminar
Polyurethane.
After a couple of years, the wings looked like surface of El Mirage Dry Lake
in Southern California.
The old gelcoat pieces were not coming off but the cracks and fissures in
the paint were obvious to the most casual observer.
However, this Phoebus is still flying and it has been probably 15 years since
sprayed.
GA
JJ Sinclair
I would only add one data point. You said>>>>>>>>>>>>There must always be
concern about an underlying
(but now covered) crack propagating into the laminate.
I have ground out literally hundreds of cracks in gel-coat that went right down
to the fiberglass laminate. To date, I haven't seen any gel-coat cracks that
entered the underlying structure. Not saying it can't happen, just haven't seen
it in going on 30 years of smelling fiberglass dust. BTW, I'm talking about
pure gel-coat cracks, not surface cracks that were caused by laminate failure
underneath. That is the first question that a repairman asks, Is this a
gel-coat crack or has the underlying structure moved?
JJ Sinclair
Paul Gaines
gelcoat cracks did indeed propagate down into the glass structure. One =
in particular was an ASW-15 where we had to zip off the entire outer =
layer of unidirectional glass in order to remove all of the cracks. =
These were crazing cracks over the entire surface, not stress cracks =
from load (crashing,etc.). A severely cracked LS-4 comes to mind as =
well. With good light and a jeweler's loop, we have noted a good =
handful of other ships that had localized crazing that had gone down =
into the structure. Speaking of down under, the Australians have noted =
this problem and issued an "AD" (or whatever they call it) concerning =
this.
Paul
Paul Gaines
final finishing process. Boats are popped out of a shiny mold and are =
basically done. Glider pieces that are gelcoated get additional sanding =
for contouring, etc.. This breaks up the surface gelcoat which, at the =
time of process, has additional "protective" cross-linking at the =
surface. This is great for contouring, but a no-no for finish =
longevity...unless you immediately paint over this surface with poly =
paint, etc..
I have noted several gliders that were refinished with poly paint where =
all of the old crazing was not removed. One $10K, 2-seater refinish job =
has cracks returning after 3 years.
Paul=20
Ken Kochanski
I have had excellent results with a 'partial' gelcoat removal/refinish ...
repainted with Simtek Prestec ... fuse 5 years old, still perfiect ... as
are wings 3 and 2 years since refinish. This is a lot of work, BTW.
Documented on SRA site ...
http://sailplane-racing.org/Articles/ASW20/asw20_wing.htm
BTW ... did I say this is a lot of work. JJ ... apologize for stealing your
punch line. :-)
KK
Ken Kochanski
"Ian Forbes" <ifo...@nospam.zsd.co.za> wrote in message
news:ovfdb1-...@zslic.forbes.zsd...
Dave Nadler YO
been checked for proper mass-balance, and for many gliders is likely
way out of spec - flutter hazard and not airworthy. If you refinish
over cracked gelcoat, the cracks will continue to propagate upwards
through the finish and downwards into the laminate - not airworthy
and hidden.
A reputable and knowledgable mechanic will sign off neither of
these "shortcuts".
Be careful out there,
Happy Holidays, Dave
PS: Yes, I have seen gliders where these shortcuts were taken,
and yes, it caused serious problems later.
Ian Forbes <ifo...@nospam.zsd.co.za> wrote in message news:<ovfdb1-...@zslic.forbes.zsd>...
Reuben
I agree that this additional surface work could lead to, down the
road problems. I do not think this is because of changes in the
crosslinking, at least not entirely. Crosslinking is the bridging of
the loose ended polymer chains. By designing the polymer of choice (in
this case gelcoat) to undergo crosslinking you create one giant
supermolecule. And during the painting process as long as each
additional coat is applied before the crosslinking is finished, each
additional coat will add to the matrix. But after the fact this
chemical reaction will not take place to the same extent and a
mechanical bond becomes the order of the day, hence the surface
roughing requirement during repairs.
*As a side note: the amount of crosslinking involved plays a large
part in the amount of flexibility a finish will have. By using a flex
additive you can inhibit the crosslinking in some or all of the paint.
My company's work with interfacial chemistry has long shown however,
that like a lot of polymers, even gelcoat is semi-permeable to water.
So, for example when you wash your glider, then dry it and finally wax
it (because it is all clean now, right?), your drying was never really
able to extract the water from the pores. The wax seals it in and
capillary action along with other hydroscopic forces pull (or drive)
the water in deeper where it freezes and expands, pushing against the
sanding scratches which now become stress risers, ultimately leading
to microcracks which propagate to larger cracks. Without the wax the
water is free to go, to and from, as external and internal forces
change usually in relationship to the seasons or prevailing weather
conditions.
Reuben
Paul Gaines <REMOVE_TO_REP...@mindspring.com> wrote in message news:<bs1te2$8hmpb$1...@ID-49798.news.uni-berlin.de>...
Stewart Kissel
Fascinating post, would not waxing increase UV damage?
JJ Sinclair
It sounds like we have finally found someone who actually knows what they are
talking about. Your post brings up several questions:
> for example when you wash your glider, then dry it and finally wax
>it (because it is all clean now, right?), your drying was never really
>able to extract the water from the pores.
Should we be waxing gelcoat? How about urethane finishes?
I have seen little blisters that form when a sailplans is left in a very wet
environment, like a metal trailer. When these blisters are popped, a little bit
of water is evident under each blister. I have seen this in urethane and also
in gelcoat (Prestec) What is your take on this?
JJ Sinclair
John Galloway
>Oh My, Ruben
>It sounds like we have finally found someone who actually
>knows what they are
>talking about. Your post brings up several questions:
>
>>and finally wax
>>it (because it is all clean now, right?), your drying
>>was never really
>>able to extract the water from the pores.
>
>
>I have seen little blisters that form when a sailplans
>is left in a very wet
>environment, like a metal trailer. When these blisters
>are popped, a little bit
>of water is evident under each blister. I have seen
>this in urethane and also
>in gelcoat (Prestec) What is your take on this?
>
>JJ Sinclair
Ruben's post is really interesting and he makes a very
strong case for water exerting a damaging shear force
between phsically bonded coating layers a refinished
glider and for exacerbating cracking - but is it the
whole story for gliders with their original finish?
I think Bob Lacovara also knows what he is talking
about - see his posting of 04-42 on 6th December and
also his article (and qualifications) at:
http://www.wingsandwheels.com/Weather%20Block%20Tech.htm
I will take a lot of convincing not to cover my glider
with a UV protectant wax and, preferably, to have a
PU finish to reduce the risk of surface crazing from
UV degredation.
Having suffered badly from water filled blisters on
one glider I am very conscious of the effects of moisture
but it seems, from what is written about experiences
in the boating world, moisture will get in through
the composite structure to the gelcoat from the inside
out in wet conditions. The boating people say that
the water dissolves chemicals out of the resin on its
way through and that the water in the blisters tastes
chemical but when I tried it on water from our Discus
fuselage blisters it was pretty tasteless.
For crazing I think that UV surface damage top old
gelcoat is the main enemy and water can then start
to penetrate from the outside. Meantime, in damp conditions,
water has been penetrating from inside from new and
this can cause blisters even in gliders with less porous
coatings
So my plan is to get a PU finish, use Wx Seal/Block
during really dry spells of weather to keep the external
surface as impervious to water and UV as possible and
to store the glider in as uv-free dry conditions as
I can achieve.
John Galloway
Paul Gaines
I will check and rephrase my "cross-linking" term. I would like B. =
Lacovara to explain the additional protection afforded at the surface of =
a very shiny, smooth de-molded gel-coat part that is not aggressively =
sanded/polished. I do know that in many cases this cracking/crazing =
follows the exact pattern of the sanding strokes/motions that are =
performed at the factories. Note the cord-wise cracking on LS products. =
They used to do much of the sanding in that direction. They also used =
jitter bug type sanders on the back bones of the fuselages. You can =
observe these "eyelash" shaped cracks all down the surface of the spines =
of many LS gliders. Schleicher's wing control surfaces crack =
span-wise...the direction of sanding. Final grit numbers and direction =
of sanding and follow-up polishing can make a huge difference in surface =
longevity too. This was explained to me an a very large repair facility =
in Germany a number of years ago when they demonstrated span-wise final =
sanding in two stages, followed by a chord-wise direction of the polish =
machine. DG employs this technique. Lacovara's paper confirms that =
surface "roughness" allows faster degradation on several levels. You =
can increase the life of your factory gel-coat finish by sanding the =
surface with 1500-2000 grit paper and polishing ACROSS this sanded =
pattern, increasing the gloss. There are a number of polishes suitable =
for this, including the hard stick polishes used by the factories and =
3M's Finesse it and Perfect it systems, just to name a couple. Follow =
this up with WX seal/block system, and you are well on your way to a =
happier gel-coat surface. =20
Dry out your ship, slick it up, use WX block system once, preferably =
twice a year, NEVER tie it out, and store it in your trailer inside a =
basement or hanger, etc..
P. Gaines=20
Papa3
My old LS-4 was partially refinished in Prestec about 5 years before I
bought it. It was clearly an Earl Scheib special (for those of you outside
the US - Earl Scheib = cheap auto refinisher of marginal quality). Within
2 years of my purchase, significant checking appeared in several areas.
Inspection with a 4x loop seemed to indicate that the crazing came from the
substrate (old gelcoat) not the outer surface. I think it just reinforces
the conventional wisdom that any areas of loose or badly crazed gelcoat need
to be removed prior to any sort of refinish.
"Ian Forbes" <ifo...@nospam.zsd.co.za> wrote in message
news:g2emrb...@192.168.2.7...
DBrotto
sages recommend for removing leading edge bugs? Seems that water would be a
violation of gel coat etiquette?
BTW, I'm a fan of WX Seal/Block. It did wonders for my LS-1f and use it 2 times
a year on my -8.
Danny Brotto
Reuben
> Oh My, Ruben
> It sounds like we have finally found someone who actually knows what they are
> talking about. Your post brings up several questions:
>
> > for example when you wash your glider, then dry it and finally wax
> >it (because it is all clean now, right?), your drying was never really
> >able to extract the water from the pores.
>
> Should we be waxing gelcoat? How about urethane finishes?
I think for this group, no.
>
> I have seen little blisters that form when a sailplans is left in a very wet
> environment, like a metal trailer. When these blisters are popped, a little bit
> of water is evident under each blister. I have seen this in urethane and also
> in gelcoat (Prestec) What is your take on this?
I have seen this. I don't have the one for all answer here, but I do
know that PPG is very quick to caution sanding the primer/filler too
thin, as it can cause lifting to occur. I think that once water finds
this void it will begin to collect with the water's own surface
tension drawing in more. And water can absolutely migrate from the
inside out.
I do think it is a part of the story with factory new finishes as much
as it is for refinishes, repairs, etc. The water really does not care
and all the work is done by humans who have been known to error.
I saw another question asking about UV. And folks, all of this is for
your reading pleasure (or perhaps not), so don't lose sleep.
So, does not waxing increase UV damage compared to a structure waxed
with a UV inhibitive wax? More complex question and looking at the
weekend owner/flier only, I would say yes, but not at a level you
would notice. Why? Because it is cumulative and mechanical damage
would more than likely occur first on a gross level before the effects
of UV were keeping you down. What about the white chalky stuff? Sure,
oxidized, damaged, UV affected topcoat. Buff it off and go fly. How
much UV exposure does your glider see in the box? How much, if left
rigged over night, in the dark? I might be going out on a limb here,
but I say very little. What would the group here say this flier flies
in a calendar year? 50 hours, more? If I chose 50 hours added 25
percent (for time not spent flying, rigging, staged on the line and so
forth) to represent the time of total exposure to the UV for the year.
That is 62.5 half hours for that year, right? At the end of ten years
we would have 625 hours. Not quite a month's worth of continuous UV
exposure. What about 20 years for this owner. 1250 hours. Just shy of
two months of continuous exposure. If your topcoat of choice can't
handle that, Oh boy. What about in your region's winter months when UV
intensity is generally at its lowest level. Hmmm.
Reuben
Interface Sciences Corporation
President / Director of R&D
www.interfacesciences.com
A&P / IA
California teaching credential in 'Plastic and Composite
Manufacturing'
>
>
>
>
> JJ Sinclair
Paul Gaines
block. There is a VERY noticeable difference of yellowing on areas not =
protected. This has been over a 5 year period. As a UV blocker, WX =
block seems to work as advertised.
Paul
B Lacovara
cracks (fortunately a majority of glider cracking) are confined within the gel
coat film, and are a product of the performance of the gel coat. More critical
in nature, are cracks resulting from localized laminate fatigue. Many times the
first indication is a gel coat crack *before* the laminate actually shows a
visible crack. This is the situation of concern if the cracks are covered. The
laminate should be thoroughly inspected after the gel coat is removed,
particularly on older, high time or hard use ships.
Bob
Reuben
posting about boats and gliders and was written towards that. During
my tenure at Scaled Composites, we never molded a finish (i.e. sprayed
into mold then laid up parts) 1: because of the need to perform
additional external work to the structure 2: hard to control thickness
of coating when using a spray on coating. This variation can distort
fibers in subtle ways possibly changing designed performance
chacteristics of that structure, but also this variation in thickness
in the coating can play havoc on itself. Temperature cycling will
cause this coating to contract and expand. Areas of thicker material
do this more or less than surrounding material of relatively
consistent thickness. This leads to stress which if given a focal
point, over time can materialize as a surface crack or other anomaly.
With gelcoat and other polyester topcoats(or fillers) shrinking about
1% during their cure, one must wait a sufficient amount of time before
sanding. If done to early the finish contracts around the scratches
imposing a force of sufficient magnitude to generate a crack.
Then at Scaled, aircraft where finished in acrylic enamels or
urethanes and today they use primarily urethane, but they still only
sand to 600 grit when they sand. Folks as a crew chief for one of the
high altitude test vehicles I can tell you that it's seven year old
finish (it's age when I left) never showed any ill effects. 66 foot
wing span 65,000 feet designed operating altitude. And we never waxed
any of the aircraft there including this one. I think sanded
structures done incorrectly or cared for improperly will lead to
cracking eventually, but one must objectively identify and observe the
mode of failure. On their own did the sanding scratches exert enough
force to initiate a crack? Or did something else complete the
triangle?
Reuben
Paul Gaines <REMOVE_TO_REP...@mindspring.com> wrote in message news:<bs5f3m$9ci9j$1...@ID-49798.news.uni-berlin.de>...
Stewart Kissel
a 17 year
old ship with some cracking on the wings. From your
experience
with composites, should I go poly or gel? And should
I have all
the old gel taken off, even if this will be more money?
Ian Forbes
> With respect, you cannot establish good practice by
> totting up numbers of for and against contributions
> to RAS.
No, but by spending a few hours trolling RAS, I can avoid making an
expensive mistake.
There has been quite a lot of feedback on this topic, and I have also
received a number of private responses by e-mail.
Clearly the situation is not that simple. But from the feedback I think
I can draw a few conclusions:
- The old gel coat should be removed, based on condition, not on
principal. This is a tough call, as no two people will have the same
assessment of any glider. Definitely all loose, flaking or damaged gel
coat must come off. The tough call is how deep does one go to remove
micro cracks. If you go down to glass you have extra work and/or
complications applying the new coating onto the glass surface and
restoring the profile.
- There is some debate over whether or not to use power tools. It seems
JJ's "air file" is the weapon of choice for best results and least
damage to the structure. With power tools it seems possible to remove
close to all of the gel coat if you need to. See Ken's website
referenced below for a good description of the "air file".
- There is some debate as to to the choice of filler to replace the
removed gel coat. Choices are polyester based (gel coat or filler) or
polyurathane based primers.
- I am a still unsure of what is required to restore a proper
aerodynamic profile. The original gel coat gets its shape from the
mould. Fibre and resin is laminated on top to form the structure. How
uniform is the thickness of the factory gel coat? If you remove all or
most of it, then replace it with a layer of filler and sand that filler
to a smooth contour, will the resulting shape match the original
profile close enough to avoid a significant aerodynamic penalty? How
much deviation from the airfoil shape can be tolerated before a
noticeable loss in performance occurs? The commercial shops don't seem
to labour this point. Is it necessary to check the profile with profile
gauges? If so, how far back from the leading edge should one measure?
- For refinishing, polyurathane seems to have clear advantages over gel
coat. There are no obvious negatives to it either. However gel coat is
the choice of purists and it can also be blended into the existing
factory finish for a partial refinish. Gel coat refinishes seem more
susceptible premature failure than polyurathane ones.
- Reapplication is not without problems. Blow holes, silicon
contamination etc cause problems which add time/money to the project.
The other universal problem is sanding through the new coating while
attempting to restore the contour or to remove an imperfection.
- There are a couple of excellent articles by Ken Kochanski on the net:
http://sailplane-racing.org/Articles/ASW20/asw20_fuse.htm
http://sailplane-racing.org/Articles/ASW20/asw20_wing.htm
These should be compulsory reading for all of us who own sailplanes with
typical > 10 year old finishes. Thanks Ken. Ken used gel coat for his
project but the articles give good incite. Even the writeup on
replacing internal control seals is worth reading.
- It takes at least 300 hours to refinish an entire glider. Add more
time for repairs and modifications etc.
- A good job is one where the mass of material added is no more than the
mass of material removed. However I doubt anybody ever achieves this
objective.
- The factory finish on many gliders delivered over the last 25 years is
a weak point. Many aircraft need re-finishing. While others (Kestrel
19m and Grob have been sighted) seem to last better. Clearly the
factory finishes have evolved around streamlining the manufacturing
process and improving the look of the delivered product. Less attention
has been paid to the longevity of the product. The suggestion that
sanding marks from the factory finish are actually the cause of gel
coat cracks is very plausible. It seems like a Good Idea to get a
polyurathane coat over the gel coat, sooner rather than later. Even DG
have come to this conclusion:
http://www.dg-flugzeugbau.com/pur-lack-e.htm
Thanks to all those who have contributed, both in RAS and in private
e-mail.
Ian
Udo Rumpf
limited experience. I have done three gliders, one of them
a complete refinish, a Cirrus. The Cirrus was done almost
ten years ago and the finish is still like new. The crazing
was extensive . The gel coat was taken off, to or near the
point of making contact with the glas. I maintained the airfoil
shape through out the process, which caused the old gel
coat to be thicker in some areas of the wing than others.
The cracks by then were so fine, they were barely visible.
After that, several stages of reapplying gel coats were done
with sandings in-between. The key was to build and sand till no
more marking of the crazing was visible.
As for maintaining the correct shape of the airfoil, I have a
rule of thumb that it should not exceed 5% overall, but
maintain a very close tolerance when it comes to waviness.
See Dick Johnson's articles on what makes laminar flow.
I have used Duratec and a high quality gel coat, mixed at
1:5 ratio, which gives it a paint like application and finish,
which keeps the orange peel to a minimum.
I know of at least three other applications with Duratec
and the results are still good. I am convinced that the
product, because it was designed for refinishing high temp
moulds, produces a more durable result.
On later projects I used epoxy sanding primer and Urethane.
It is a bit more difficult to sand the finish coat, but the results
are worth it.
Regards
Udo
"Ian Forbes" <ifo...@nospam.zsd.co.za> wrote in message
news:j78kb1-...@zslic.forbes.zsd...
Silent Flyer
with the gelcoat on the Kestrel 19.
The two Kestrels that I owned had no gelcoat cracking up to ten years after
manufacture, although one of them developed shrinkage along the spar line.
In Martin Simons book on Slingsby sailplanes he makes reference to the fact
that George Burton, the managing director, was unable to get the wings on
the Vega produced to the waviness standard of the german gliders then in
production. Presumably this was because the time consuming process of
sanding the wings after removal from the mould would have cost too much.
If this was the case then probably the Kestrel wings also were not sanded ?
Can anyone comment on the longevity of the finish on the Vega ?
Was it the material used on the Kestrel or the possible lack of sanding that
contributed to the lack of cracking problems ?
DB
Andy Durbin
> Dry out your ship, slick it up, use WX block system once, preferably =
> twice a year, NEVER tie it out, and store it in your trailer inside a =
> basement or hanger, etc..
>
> P. Gaines
Why *NEVER tie it out*. Is your concern UV, moisture, or something
else? My ship is based in Phoenix, AZ where the humidity is usually
very low. Most of my fellow club pilots tie down for the duration of
a contest.
When I go to New Mexico or Texas I see dew on the wings in the
morning. Why should I be concerned about a little moisture on the
wings if I put 30 gallons inside them for 6 or more hours each contest
day?
Andy (GY)
Paul Gaines
really should not be. I think it is always better practice not to leave a
ship outside. Wider temp swings, etc...
Paul
----- Original Message -----
From: "Glider Pilot Network" <w...@gliderpilot.net>
To: "Paul Gaines" <compo...@mindspring.com>
Sent: Tuesday, December 23, 2003 9:40 AM
Subject: [r.a.s] Re: Refinishing: Who has tried a shortcut?-U out there JJ?
> ------------------------------------------------------------
> Newsgroup: rec.aviation.soaring
> Subject: Re: Refinishing: Who has tried a shortcut?-U out there JJ?
> Author: Andy Durbin <a.du...@netzero.net>
> Date/Time: 14:30 23 December 2003
> ------------------------------------------------------------
> Paul Gaines wrote in message news:...
>
>
> > Dry out your ship, slick it up, use WX block system once, preferably
> =
> > twice a year, NEVER tie it out, and store it in your trailer inside a
> =
> > basement or hanger, etc..
> >
> > P. Gaines
>
>
> Why *NEVER tie it out*. Is your concern UV, moisture, or something
> else? My ship is based in Phoenix, AZ where the humidity is usually
> very low. Most of my fellow club pilots tie down for the duration of
> a contest.
>
> When I go to New Mexico or Texas I see dew on the wings in the
> morning. Why should I be concerned about a little moisture on the
> wings if I put 30 gallons inside them for 6 or more hours each contest
> day?
>
>
> Andy (GY)
>
> ------------------------------------------------------------
>
JJ Sinclair
1. Re-establishing the original airfoil can be done by making some *quick &
dirty* templates, before starting. Wax and PVA (mold release) several locations
along the leading edge, say every 24 inches. Now make cardboard templates for
these locations, nothing fancy, just roughly the shape. With the L/E up, lay on
about 3 strands of glass rovings around the template locations. Next, pile on
some epoxy flox and shove your cardboard templates into the goo. Pop them off,
when cured and you have some exact replicas of your original leading edge
shape. I carry my templated back about 3 inches, as this is the most critical
area. Everything else is contouring to keep a smooth shape, both spsn-wise and
cord-wise.
2. You will need a good water trap in your feed line coming from the
compressor. I have used the *toilet paper* trap for years. It employs a roll of
toilet paper as the filter element. Just replace the roll before each major
operation (each wing) Some red-neck repairmen have even been known to dry out
the used rolls and then employ them again, for their original purpose. If you
don't have a good moisture trap, your spray gun will spit out little water
drops and they will show up as little craters on the product.
Have fun and remember, Everybody's got to be doing something. You have just
chosen to sand for the rest of your life.
JJ Sinclair
Reuben
will be removing all the gelcoat that can be removed safely. I am
addicted to gelcoat though. Must be the smell.
Reuben
Stewart Kissel <REMOVE_TO_REPL...@hotmail.com> wrote in message news:<bs7cfn$9s8ni$1...@ID-49798.news.uni-berlin.de>...
John Ferguson
I have seen poor paintwork on Vegas though.
John
B Lacovara
discussion orbiting some of the comments. It would be nice if we were all in
the same room, where we could exchange a mass of information, rather than
simple RAS sound bites.
In too brief a sound bite fashion let me address a few of the comments:
The difference between boat gel coat and glider gel coat - It is a given that
boat gel coat holds up better than glider gel coat… many boat companies offer
a 10 year gel coat warranty! Boats are built with polyester gel coat and a
polyester (or vinyl ester variant) laminating resin substrate. The resulting
bond is a *COHESIVE* in nature. A previous comment was correct, that
essentially when boats come out of the mold they are finished (from a gel coat
cosmetic perspective - no sanding). The boats built today are using 4th and 5th
generation gel coat formulations that are fairly sophisticated. One small boat
company in the U.S. will use more gel coat than the entire glider industry.
Gliders, on the other hand, use polyester gel coat and an epoxy laminating
resin substrate. The resulting bond is an *ADHESIVE* force. The state-of-cure
of the gel coat applied in the mold at the time of laminate application is
critical to the bond. This is a complex interplay involving initiator level,
temperature, time, gel coat thickness, and other factors. There is an optimal
cure-state window for development of maximum bonding between the cured gel coat
and the laminate. At best, the adhesive bond between polyester and epoxy will
not produce as much energy as a polyester to polyester cohesive bond. The gel
coat typically used on gliders is the same basic 2nd or 3rd generation
technology as used on boats in the '70's and '80's. Also, there is
considerably more surface movement on a thin skinned glider laminate as
compared to a much thicker boat laminate.
Addressing a few of Ruben's comments - When gel coat is applied wet-on-wet, as
in the mold, it does cure as a uniform molecular matrix. When gel coat or a
paint coating is post-applied (as in repairs or refinishing leading edges out
of the mold) there is little, if any, crosslink bonding that occurs. This
scenario relies for the most part on a simple mechanical bond as Ruben
correctly stated.
Ah, the moisture issue….. It is correctly stated that gel coat and
composites laminates have the properties of a semi-permeable membrane. However
the discussion leaves the tracks with the idea of liquid water penetration and
surface porosity. *Water vapor*, that is individual molecules of H2O, will
continually seek to equilibrate on the inner and outer skins of a laminate in a
very slow process. Water in the liquid state will *not* penetrate gel coat.
The surface pores and voids in the 3-D molecular matrix are too small for
liquid phase water to penetrate. This has to do with the inherent surface
tension of liquid H2O. The surface does not wet enough for liquid to flow into
the normal porosity.
You *do not* have to be concerned about washing your glider with water, or
leaving it out in the rain for that matter. It will not have a negative effect
on the gel coat. Wax does not seal in water. Vapor phase H2O will freely
equilibrate with no noticeable retardation of transmission through a wax film.
Additionally, since liquid water is not present within the gel coat or laminate
matrix, (under normal circumstances - let's not talk osmotic blisters), there
is no issue with freezing and causing cracks. This could become an issue with
giant cracks, but not with typical gel coat effects. Freezing water is simply
not an issue.
Again, hope this helps…. After 38 rounds this thread has stayed coherent….
has to be a record for RAS!
Bob Lacovara
B Lacovara
of the mold) there is little, if any, crosslinking that occurs. This scenario
B Lacovara
Richard Pfiffner
If what you say about the 2nd or 3rd generation gel coat used in the boat of
the 70s and 80s is true and the assumption that moisture is not a problem
with gel coat how do you account for the horrible blister problems below the
waterline of many of the boats of the 70 and 80s. I experience this with
sailboat in the early 80s. The blister were full of liquid. A large number
of boats in the area where I sailed had this problem. It was not boat
manufacture specific.
Richard Pfiffner
"B Lacovara" <blac...@aol.com> wrote in message
news:20031223145117...@mb-m03.aol.com...
> This thread has become very interesting.. there is considerable technical
> discussion orbiting some of the comments. It would be nice if we were all
in
> the same room, where we could exchange a mass of information, rather than
> simple RAS sound bites.
>
> In too brief a sound bite fashion let me address a few of the comments:
>
> The difference between boat gel coat and glider gel coat - It is a given
that
> boat gel coat holds up better than glider gel coat. many boat companies
> Ah, the moisture issue... It is correctly stated that gel coat and
> Again, hope this helps.. After 38 rounds this thread has stayed coherent..
B Lacovara
Interestingly enough, boat hull blistering is not a gel coat problem, but
rather a laminate problem. Considering the laminate as a semi-permeable
membrane the potential for osmosis can take place. Osmosis is the tendency of a
fluid of lower concentration to pass through a semi-permeable membrane into a
solution of higher concentration. In the case of boat hulls, water vapor (lower
concentration) passes from the inside of the hull to the outside of the hull
(higher concentration). The gel coat matrix is denser than the laminate matrix
and the transmitted water vapor will eventually collect in what are known as
seed sites. These are voids at the gel coat/laminate interface. Eventually, the
liquid in the seed sites will become denser that the outside water and the
process reverses pulling water in from the opposite direction…. This is where
the big nasty boat hull blisters appear. Blistering problems have been solved
by the boat or swimming pool industries, because they now use vinyl ester skin
coats behind the gel coat. The point is that the problem was solved with a
laminate modification, rather than a gel coat modification.
The reason I was trying to avoid this discussion, is that this mechanism is not
in play in relation to gel coat cracks. Sailplane gel coat, or more likely
urethane paint, can blister from osmosis. Just put a glider in a wet fuselage
cradle! However, until the seed site is saturated and dense there is no
transport of *liquid water*. All the moving H20 is vapor phase. This only
happens under very specific conditions. So unless you are going to ride it
hard and put it away wet there is absolutely issue with washing a gel coat
finish. But even when blistering takes place, there is no relation to typical
gel coat cracking.
Bob Lacovara
Richard Pfiffner
Thanks for the explanation. Do you think osmosis be a problem with gliders
such as the discus or ventus which have a wet wing.
Richard Pfiffner
"B Lacovara" <blac...@aol.com> wrote in message
news:20031223161947...@mb-m03.aol.com...
> I was actually trying to avoid this part of the discussion, but here
goes...
> Interestingly enough, boat hull blistering is not a gel coat problem, but
> rather a laminate problem. Considering the laminate as a semi-permeable
> membrane the potential for osmosis can take place. Osmosis is the tendency
of a
> fluid of lower concentration to pass through a semi-permeable membrane
into a
> solution of higher concentration. In the case of boat hulls, water vapor
(lower
> concentration) passes from the inside of the hull to the outside of the
hull
> (higher concentration). The gel coat matrix is denser than the laminate
matrix
> and the transmitted water vapor will eventually collect in what are known
as
> seed sites. These are voids at the gel coat/laminate interface.
Eventually, the
> liquid in the seed sites will become denser that the outside water and the
> process reverses pulling water in from the opposite direction.. This is
Greg Arnold
B Lacovara wrote:
The boats built today are using 4th and 5th
> generation gel coat formulations that are fairly sophisticated. One small boat
> company in the U.S. will use more gel coat than the entire glider industry.
>
> Gliders, on the other hand, use polyester gel coat and an epoxy laminating
> resin substrate. The resulting bond is an *ADHESIVE* force. The state-of-cure
> of the gel coat applied in the mold at the time of laminate application is
> critical to the bond. This is a complex interplay involving initiator level,
> temperature, time, gel coat thickness, and other factors. There is an optimal
> cure-state window for development of maximum bonding between the cured gel coat
> and the laminate. At best, the adhesive bond between polyester and epoxy will
> not produce as much energy as a polyester to polyester cohesive bond. The gel
> coat typically used on gliders is the same basic 2nd or 3rd generation
> technology as used on boats in the '70's and '80's. Also, there is
> considerably more surface movement on a thin skinned glider laminate as
> compared to a much thicker boat laminate.
Would gliders avoid the problem if they used the 4th and 5th generation
gel coat formulations? If so, why have the glider companies chosen to
use an older technology?
B Lacovara
Second, the water is not in the tanks long enough to be a problem. One would
have to leave the tanks filled for an extented period, maybe weeks?, to even
have the potential for a problem. So far I have never seen or heard of a wet
wing problem.
Reuben
I appreciate the feedback. We are definitely smarter as a collective
mind and I like your stuff. On the side my company has a nanotech
development that I think you will find interesting as to how it
affects composite structures. Drop me a line sometime.
Let me point out that I have seen SEM pictures of a gelcoat substrate
that did indeed have its pores closed shut by waxing. This was also
confirmed through contact angle measurements compared to a non-waxed
sample. The same energy change that forces the water to bead
externally will repel water internally away from the surface in the
same manner.
Bob, the below text in parenthesis only is your own is it not?
Taken from: http://www.wingsandwheels.com/Weather%20Block%20Tech.htm
“Effects of Porosity
Polyester gel coat appears, under the microscopic, a
very porous material. Porosity poses several problems that effect gel
coat weathering performance. First, the wall of an individual pore
increases the effective surface area in a localized area. There is
also a relatively sharp edge at the intersection of the surface and
the vertical wall of the pore. This sharp edge is subject to
photo-initiation. Second, porosity tends to collect micro-debris. This
could include general dirt, buffing compound, wax, oils etc. The
reactivity of the debris filling the porosity is a potential
problem.â€
If oil can enter the pores and silicone can migrate through by pore
access, why can’t water (vapor or liquid) move into the gelcoat
substrate, which compared to these two can have a surface tension only
slight higher when conditions are right, but a smaller molecular size
than both to offset? These pores appear as garage doors to the small
water molecules? It would seem to me if water is inside and you seal
the way out, it has no where to go but in further. Add a little soap
to the water and/or increase the temperature of the water, and its
surface tension drops increasing the water’s wetting action allowing
it to penetrate the pores even easier.
For those interested DG has the following published article available
for review:
http://www.dg-flugzeugbau.de/gelcoat-e.html
Washing your glider is an unavoidable circumstance. Gelcoat can be
very permeable to water. I agree large droplets of water will not
absorb through before they evaporate. My point (which I should have
elaborated further) was that it is not that which you can remove that
will cause problems. I have to bring it up, Bob, I know you said not
to, but I have to, with the gelcoat acting as a semi-permeable
membrane and entrained moisture present (its there), add a little
hydrolysis and osmotic action exists here on a small scale for sure,
osmotic action can and does move in a small amount of H20, albeit in
only one direction, but what goes in must be able to come out
(regardless of the mode of entry) to achieve balance. If the driving
force is in, well this fundamental action is a basis for the theory of
hydraulics. (Liquids are for all purposes non-compressible). You can
seal the outside (at least we try), but current manufacturing methods
for gliders do not allow this for the internal side. With no way out
for this moisture the water has no choice but seek the path of least
resistance, which will lead to collecting in any void, SEM pictures
show that these structures are not necessarily homogeneous, so there
will be plenty of interlaminar spaces, pinholes, microscopic stress
cracks, etc. Water does freeze, vapor phase (note: vapor changes via
'deposition' like frost on the ground and bypasses liquid state
completely) or liquid phase, these hexagonal crystals just don’t fit
neatly in the same space, if left to repeat they will cause a failure.
I believe the most visible indicator of this is cracking, simply
because of the vast quantity of sanding scratches to serve as stress
risers. A rheometric measurement will support this. This was put in
place long ago. The purpose of my first posting was “to wax or not
to wax†, as such I say not waxing far outweighs the benefits of
waxing.
If we continue this can we start a new thread?
Reuben
blac...@aol.com (B Lacovara) wrote in message news:<20031223135444...@mb-m03.aol.com>...
> This thread has become very interesting…. there is considerable technical
> discussion orbiting some of the comments. It would be nice if we were all in
> the same room, where we could exchange a mass of information, rather than
> simple RAS sound bites.
>
> In too brief a sound bite fashion let me address a few of the comments:
>
> The difference between boat gel coat and glider gel coat - It is a given that
> boat gel coat holds up better than glider gel coat… many boat companies offer
> Ah, the moisture issue….. It is correctly stated that gel coat and
> composites laminates have the properties of a semi-permeable membrane. However
> the discussion leaves the tracks with the idea of liquid water penetration and
> surface porosity. *Water vapor*, that is individual molecules of H2O, will
> continually seek to equilibrate on the inner and outer skins of a laminate in a
> very slow process. Water in the liquid state will *not* penetrate gel coat.
> The surface pores and voids in the 3-D molecular matrix are too small for
> liquid phase water to penetrate. This has to do with the inherent surface
> tension of liquid H2O. The surface does not wet enough for liquid to flow into
> the normal porosity.
>
> You *do not* have to be concerned about washing your glider with water, or
> leaving it out in the rain for that matter. It will not have a negative effect
> on the gel coat. Wax does not seal in water. Vapor phase H2O will freely
> equilibrate with no noticeable retardation of transmission through a wax film.
> Additionally, since liquid water is not present within the gel coat or laminate
> matrix, (under normal circumstances - let's not talk osmotic blisters), there
> is no issue with freezing and causing cracks. This could become an issue with
> giant cracks, but not with typical gel coat effects. Freezing water is simply
> not an issue.
>
> Again, hope this helps…. After 38 rounds this thread has stayed coherent….
Reuben
If we continue this let's start a new thread?
Reuben
blac...@aol.com (B Lacovara) wrote in message news:<20031223161947...@mb-m03.aol.com>...
> I was actually trying to avoid this part of the discussion, but here goes…..
> Interestingly enough, boat hull blistering is not a gel coat problem, but
> rather a laminate problem. Considering the laminate as a semi-permeable
> membrane the potential for osmosis can take place. Osmosis is the tendency of a
> fluid of lower concentration to pass through a semi-permeable membrane into a
> solution of higher concentration. In the case of boat hulls, water vapor (lower
> concentration) passes from the inside of the hull to the outside of the hull
> (higher concentration). The gel coat matrix is denser than the laminate matrix
> and the transmitted water vapor will eventually collect in what are known as
> seed sites. These are voids at the gel coat/laminate interface. Eventually, the
> liquid in the seed sites will become denser that the outside water and the
> process reverses pulling water in from the opposite direction…. This is where
Scott Correa
"Greg Arnold" <soa...@REMOVEcox.net> wrote in message
news:y25Gb.21786$J77.6384@fed1read07...
> Would gliders avoid the problem if they used the 4th and 5th generation
> gel coat formulations? If so, why have the glider companies chosen to
> use an older technology?
>
The answer is probably no. The adhesive nature of the bond would still be
inferior to the cohesive bond of an all polyester or vinylester system.
The reason for not making the change is that the current products used
conform with the type certificate and they are known quantitys with
acceptable
service lives (in the factorys eyes). Making a change introduces many
unknowns,
at least in the minds of the designers. This is a case of accepting the
current state
of affairs with the perception that changes might be more painful than
living with
todays reality.....
Scott.
Thomas Knauff
inexperienced person removing gel coat.
It is very difficult work and short-cuts are tempting. Few, if any short
cuts are possible for fear of damaging the structural layers of fiberglass,
carbon or whatever.
Doing it wrong can result in an unsafe glider. For this reason, it is
probably unwise to purchase a refinished glider if it was not done by a
professional.
Tom Knauff
"Reuben" <reuben...@interfacesciences.com> wrote in message
news:6ef8fee3.03122...@posting.google.com...
> Bob,
>
> I appreciate the feedback. We are definitely smarter as a collective
> mind and I like your stuff. On the side my company has a nanotech
> development that I think you will find interesting as to how it
> affects composite structures. Drop me a line sometime.
>
> Let me point out that I have seen SEM pictures of a gelcoat substrate
> that did indeed have its pores closed shut by waxing. This was also
> confirmed through contact angle measurements compared to a non-waxed
> sample. The same energy change that forces the water to bead
> externally will repel water internally away from the surface in the
> same manner.
>
> Bob, the below text in parenthesis only is your own is it not?
> Taken from: http://www.wingsandwheels.com/Weather%20Block%20Tech.htm
>
> “Effects of Porosity
> Polyester gel coat appears, under the microscopic, a
> very porous material. Porosity poses several problems that effect gel
> coat weathering performance. First, the wall of an individual pore
> increases the effective surface area in a localized area. There is
> also a relatively sharp edge at the intersection of the surface and
> the vertical wall of the pore. This sharp edge is subject to
> photo-initiation. Second, porosity tends to collect micro-debris. This
> could include general dirt, buffing compound, wax, oils etc. The
> reactivity of the debris filling the porosity is a potential
> problem.”
>
> If oil can enter the pores and silicone can migrate through by pore
> access, why can’t water (vapor or liquid) move into the gelcoat
> substrate, which compared to these two can have a surface tension only
> slight higher when conditions are right, but a smaller molecular size
> than both to offset? These pores appear as garage doors to the small
> water molecules? It would seem to me if water is inside and you seal
> the way out, it has no where to go but in further. Add a little soap
> to the water and/or increase the temperature of the water, and its
> surface tension drops increasing the water’s wetting action allowing
> completely) or liquid phase, these hexagonal crystals just don’t fit
> neatly in the same space, if left to repeat they will cause a failure.
> I believe the most visible indicator of this is cracking, simply
> because of the vast quantity of sanding scratches to serve as stress
> risers. A rheometric measurement will support this. This was put in
> place long ago. The purpose of my first posting was “to wax or not
> to wax”, as such I say not waxing far outweighs the benefits of
> waxing.
>
> If we continue this can we start a new thread?
>
> Reuben
>
>
> blac...@aol.com (B Lacovara) wrote in message
news:<20031223135444...@mb-m03.aol.com>...
> > This thread has become very interesting…. there is considerable
technical
> > discussion orbiting some of the comments. It would be nice if we were
all in
> > the same room, where we could exchange a mass of information, rather
than
> > simple RAS sound bites.
> >
> > In too brief a sound bite fashion let me address a few of the comments:
> >
> > The difference between boat gel coat and glider gel coat - It is a given
that
> > boat gel coat holds up better than glider gel coat… many boat
> > Ah, the moisture issue….. It is correctly stated that gel coat and
> > Again, hope this helps…. After 38 rounds this thread has stayed
coherent….
John Galloway
Your postings are the first I have ever printed from
RAS for reference.
When addressing the question of to what extent liquid
water can penetrate a gelcoat surface and whether or
not to wax, would either of you be prepared to comment
on whether reduction of gelcoat surface deterioration
by using a UV filtering polish (e.g. Wx/block + Wx/seal)
will have a significant effect on the ultimate advice?
Apart from crazing a non waxed weathered vorgelat
gelcoat also eventually goes dry and powdery and looks
and feels like it would soak up liquid water into its
surface layer more easily than a highly polished and
uv protected (by polish or covers/hangaring) gelcoat.
BTW, and in support of the opposite point of view,
I have been in the sad position of monitoring a friend's
Std Cirrus that has not been out of its metal non insulated
trailer in Scotland for 10 years. The fuselage was
rebuilt in about 1981 and painted in vorgelat. The
wings are original Scwabbellack. Both were fine in
1993 but since then, in the dark, the fuselage has
crazed dramatically and became dull and powdery so
that (before I polished it a year or so ago) you could
get your clothes white by coming into contact with
it. This expensive unintended experiment confirms
that gelcoat can definitely detriorate very badly in
the virtual absence of UV. Is this just moisture or
does vorgelat gelcoat just molecularly age no matter
what?
It would be fascinating to store gelcoat glider samples
in a typical glider trailer in the dark - some polished
and some not - and to see whether it polish does or
does not prevent moisture and temperature gelcoat deterioration
in the absence of UV.
Supplementary question - if cost was not an issue would
you get a new glider painted in PU or T35?
John Galloway
B Lacovara
can do in this forum........
<<<<<<<When addressing the question of to what extent liquid water can
penetrate a gelcoat surface and whether or not to wax, would either of you be
prepared to comment
on whether reduction of gelcoat surface deterioration by using a UV filtering
polish (e.g. Wx/block + Wx/seal) will have a significant effect on the ultimate
advice?>>>>
From my perspective, the potential of gel coat damage from liquid state water
is minimal, and is a secondary debate. We have conducted tens of thousands of
hours of testing within the composites industry on gel coat weathering
performance. A narrow band within the UV spectrum range is the primary source
of surface degradation. Thousands of hours of testing have also shown that
surface degradation can be significantly slowed with the routine application of
a UV inhibited surface agent. Please understand that as the original developer
of the Wx/Block & Wx/Seal products I could be viewed as being bias in this
portion of the discussion. However, my goal is to offer valid science without a
commercial bias. The data on waxed vs. non-waxed gel coat surfaces indicates a
UV effective wax significantly delays color change and the results of
photo-oxidation. Better than test results, we seem to have a good history over
the last 10-years with maintaining gel coat finishes by using an UV effective
wax.
<<<<Apart from crazing a non waxed weathered vorgelat gelcoat also eventually
goes dry and powdery and looks and feels like it would soak up liquid water
into its
surface layer more easily than a highly polished and uv protected (by polish or
covers/hangaring) gelcoat.>>>>>>>
This is typically the effects of photo-oxidation that causes molecules to sluff
off the surface. Polishing "wets" the surface and reduces the powderly look,
while consolidating the loose micro-particles.
<<<<<< Both were fine in 1993 but since then, in the dark, the fuselage has
crazed dramatically and became dull and powdery so that (before I polished it a
year or so ago) you could get your clothes white by coming into contact with
it. This expensive unintended experiment confirms that gelcoat can definitely
detriorate very badly in the virtual absence of UV. Is this just moisture or
does vorgelat gelcoat just molecularly age no matter what?>>>>>>
Gelcoat is a very quirky coating, no doubt. This phenomenon is known but not
currently explained. It is technically termed "box yellowing". There is a very
different mechanism at work here…. something different than UV degradation.
We postulate it may have to do with a reduced crosslinking density at the time
of original cure; I am currently part of a technical task force studying this
specific problem. To date no results - the first round of testing by the gel
coat manufacturers did not yield conclusive data.
<<<<<It would be fascinating to store gelcoat glider samples in a typical
glider trailer in the dark - some polished and some not - and to see whether it
polish does or does not prevent moisture and temperature gelcoat deterioration
in the absence of UV.>>>>>
It would be a great experiment, but to be meaningful there would have to be a
large enough sample group to avoid jumping to conclusions based on anecdotal
evidence.
<<<<<Supplementary question - if cost was not an issue would you get a new
glider painted in PU or T35?>>>>>
In my opinion, a linear polyurethane paint (properly applied) is better than
gel coat on gliders. For what it's worth my glider has factory finish PU.
Bob Lacovara
Eric Greenwell
> What would the group here say this flier flies
> in a calendar year? 50 hours, more? If I chose 50 hours added 25
> percent (for time not spent flying, rigging, staged on the line and so
> forth) to represent the time of total exposure to the UV for the year.
> That is 62.5 half hours for that year, right? At the end of ten years
> we would have 625 hours. Not quite a month's worth of continuous UV
> exposure. What about 20 years for this owner. 1250 hours. Just shy of
> two months of continuous exposure. If your topcoat of choice can't
> handle that, Oh boy. What about in your region's winter months when UV
> intensity is generally at its lowest level. Hmmm.
A pilot that flies his glider only 50 hours a year probably should think
about selling it or getting some partners! Maybe he doesn't have to
worry about UV. Let's a take my situation:
-200 hours a year of flying (about 40 hours above 10,000 feet)
-tied out all day for about 1 week in summer at low altitudes
-tied out all day for about 2 weeks in summer at high altitudes (5000+ feet)
Breaking it down:
140 hours flying but kept in trailer
60 hours being rigged/derigged (4.5 hour flights, 30 flights)
60 hours flying but kept outside
140 hours exposure while tied down
---------
400 hours a year UV exposure - 6.4 times Reuben's example
And, many of these hours are at high altitudes in clean air, where the
UV will be much more intense.
So, should I be worried about UV exposure? When I polish my glider, I
notice the top of the wings makes my polishing rag turn white sooner
than the bottom of the wing. I believe this because the gel coat on the
top is suffering more than the gel coat on the bottom, and my guess is
it's UV.
--
-----
change "netto" to "net" to email me directly
Eric Greenwell
Washington State
USA
Phoebus_810
> At 16:00 21 December 2003, Jj Sinclair wrote:
> >Oh My, Ruben
> >It sounds like we have finally found someone who actually
> >knows what they are
> >talking about. Your post brings up several questions:
> >
> >> for example when you wash your glider, then dry it
> >>and finally wax
> >>it (because it is all clean now, right?), your drying
> >>was never really
> >>able to extract the water from the pores.
> >
> >Should we be waxing gelcoat? How about urethane finishes?
> >
> >I have seen little blisters that form when a sailplans
> >is left in a very wet
> >environment, like a metal trailer. When these blisters
> >are popped, a little bit
> >of water is evident under each blister. I have seen
> >this in urethane and also
> >in gelcoat (Prestec) What is your take on this?
> >
> >JJ Sinclair
>
> Ruben's post is really interesting and he makes a very
> strong case for water exerting a damaging shear force
> between phsically bonded coating layers a refinished
> glider and for exacerbating cracking - but is it the
> whole story for gliders with their original finish?
> I think Bob Lacovara also knows what he is talking
> about - see his posting of 04-42 on 6th December and
> also his article (and qualifications) at:
>
> http://www.wingsandwheels.com/Weather%20Block%20Tech.htm
>
> I will take a lot of convincing not to cover my glider
> with a UV protectant wax and, preferably, to have a
> PU finish to reduce the risk of surface crazing from
> UV degredation.
>
> Having suffered badly from water filled blisters on
> one glider I am very conscious of the effects of moisture
> but it seems, from what is written about experiences
> in the boating world, moisture will get in through
> the composite structure to the gelcoat from the inside
> out in wet conditions. The boating people say that
> the water dissolves chemicals out of the resin on its
> way through and that the water in the blisters tastes
> chemical but when I tried it on water from our Discus
> fuselage blisters it was pretty tasteless.
>
The boats are buildt of polyester. The hardener is an acid. In the
cured polyester there can be small amounts of acid that react with
water. That is why the water coming out of these blisters smells and
tastes chemical. Gliders are buildt whit epoxy that does not react
with water the same way. Polyestergelcoat is not a very good barrier
for water. That is why many boats are painted, under the waterline,
with an epoxybased primer.
Matts, glider pilot and boatbuilding teacher
> For crazing I think that UV surface damage top old
> gelcoat is the main enemy and water can then start
> to penetrate from the outside. Meantime, in damp conditions,
> water has been penetrating from inside from new and
> this can cause blisters even in gliders with less porous
> coatings
>
> So my plan is to get a PU finish, use Wx Seal/Block
> during really dry spells of weather to keep the external
> surface as impervious to water and UV as possible and
> to store the glider in as uv-free dry conditions as
> I can achieve.
>
> John Galloway