Re: Urethane Paint

[ND]

On Tuesday, November 10, 2015 at 9:15:39 PM UTC-5, Jonathan St. Cloud wrote:
> Any idea how much weight the urethane paint option adds to an 18 meter glider?

not enough different from gel-coat to matter unless you are really heavy or really light.

[jfitch]

On Tuesday, November 10, 2015 at 6:15:39 PM UTC-8, Jonathan St. Cloud wrote:
> Any idea how much weight the urethane paint option adds to an 18 meter glider?

I answer that in a different way: if you go with gel coat, after your first refinish you will be a LOT lighter, but the weight will have come out of your wallet.

I would not consider buying a new glider that was not PU coated.

[christoph...@googlemail.com]

Depends on the amount of filler being used, if a thin layer of glass is added (~2kg for a whole glider) and how thick the original layer of gelcoat was. There are cases where there's no weight being added. But usually, around 5kg of additional weight can be expected.

[johnsin...@yahoo.com]

If urethane is requested, the manufacturer will most likely not use gelcoat in the mold and apply the urethane finish after assembling the parts. I know my Genesis was done this way. Ready to spray urethane is about 10# per gallon and it would take about 2 gallons.
JJ

[uncl...@ix.netcom.com]

On Thursday, November 12, 2015 at 10:03:38 AM UTC-5, johnsin...@yahoo.com wrote:
> If urethane is requested, the manufacturer will most likely not use gelcoat in the mold and apply the urethane finish after assembling the parts. I know my Genesis was done this way. Ready to spray urethane is about 10# per gallon and it would take about 2 gallons.
> JJ

Not true of current production yet John. Ships are molded with gelcoat, then filled and sanded, followed by finish paint. This avoids the million pinhole problem,
Maybe at some point they will spray primer in the mold, followed by lamination. That would require knowing and tracking which parts go on a painted ship, plus some process and quality controls.
FWIW
UH

[Papa3]

I was just looking at this the other day for a project we're working on. Out of the 10 lbs or so per gallon, not all of that is solids; the solvents and some other additives will evaporate not to mention some lost to overspray. The percentage varies. It seems like 60% is a decent average, so 6lbs/gallon with about 2-3 gallons for a 15 meter glider? Call it 12-15 lbs?

P3

[Andrzej Kobus]

The gel coat sprayed in the mold is very thin. I had opportunity to look at my new glider in production, before it was moved to the paint shop.

[ifee...@hotmail.com]

5 kg. sounds like a decent ballpark estimate. My club has an '85 DG-300 which was repainted with polyurethane last year. The original gel coat had been cut polished twice and by last year was in pretty rough shape. The shop didn't remove all the old gel coat but just lightly sanded it to take care of the oxidation and crazing. Going by the before and after weighings it gained 3.1 kg.

[Jim Crawford]

At 05:11 14 November 2015, ifee...@hotmail.com wrote:
>5 kg. sounds like a decent ballpark estimate. My club has an '85
DG-300

>whi=

>ch was repainted with polyurethane last year. The original gel
coat had

>bee=

>n cut polished twice and by last year was in pretty rough shape.
The shop

>d=

>idn't remove all the old gel coat but just lightly sanded it to take
care

>o=

>f the oxidation and crazing. Going by the before and after
weighings it

>gai=
>ned 3.1 kg.
>

LS4 with very poor original gel taken to a professional refinisher (in
Poland). Aircraft gel completely stripped down to structure.
Reprofiled, T35 gel used as a filler/primer and finished in acrylic
paint (offered as option to PU). Aircraft returned looking beautiful
and ~ 1lb lighter.

Jim

[Robert M]

On Tuesday, November 10, 2015 at 7:15:39 PM UTC-7, Jonathan St. Cloud wrote:
> Any idea how much weight the urethane paint option adds to an 18 meter glider?

Not removing all the gelcoat will likely result, over time, in the cracks coming back through the urethane paint.

Removing all the gelcoat and then priming and spraying urethane paint should not result in a weight gain. Especially on older glider where there are some areas of very thick gelcoat.

It is all in how the work is done.

Robert Mudd
Composite Aircraft Repair
Moriarty, New Mexico.

[ifee...@hotmail.com]

I believe the OP was asking about getting a new glider with the optional polyurethane in which case the factory sprays the paint over the gelcoat and not about a refinish.

[Paul Crabb]

On Wednesday, 11 November 2015 02:15:39 UTC, Jonathan St. Cloud wrote:
> Any idea how much weight the urethane paint option adds to an 18 meter glider?

PU or Acrylic topcoat paint is just used as a very thin UV block, it is usually a very thin layer and is not used to "profile" the surface. If you are not concerned about the durability of your glider finish and want to maximise performance then just going with gelcoat would be the obvious choice... it also allows you to more easily reprofile the wings once they have done their "shrinking". Schempp seem to be the only glider manufacturer to largely avoid their wings looking like prunes after a few years.

If I was having a new glider I would have the fuselage, tailplane, control surfaces all done in PU and then get the wings and tip extensions painted a couple of years later once the shrinkage has stabilised and surfaces have been "profiled". If you do leave the wings bare then consider having the numbers done in cellulose so they can be easily removed prior to painting.

I would also have the underwing numbers clearcoated and faired in so there are no sharp edges left to mess with the airflow.

[son_of_flubber]

On Sunday, November 15, 2015 at 4:34:23 AM UTC-5, Paul Crabb wrote:

> PU or Acrylic topcoat paint is just used as a very thin UV block, it is usually a very thin layer and is not used to "profile" the surface.

Does the PU protect the gelcoat from temperature related crazing?
Someone told me that gelcoat crazing was attributed to rapid change in temperature associated with flying wave. Once the cracks start moisture penetrates and accelerates the deterioration.

Anyone have a crazed PU painted wing?

Anyone have a better explanation for wing crazing?

[jpg...@gmail.com]

In recent decades the temperature related cracking is an issue iparticularly affecting hard, otherwise durable, Schwabellack gelcoat on DG gliders. For other manufacturers using T35 and similar it is mostly UV and moisture that causes the degredation of the surface.

[son_of_flubber]

On Sunday, November 15, 2015 at 8:57:36 AM UTC-5, jpg...@gmail.com wrote:
> For other manufacturers using T35 and similar it is mostly UV and moisture that causes the degradation of the surface.

I heard that the cracks develop in the direction of the final sanding (front to back). My understanding is that the sanding leaves microscopic cracks in the direction of the sanding, then moisture gets into the cracks and expands them. And the PU coating seals those microcracks and slows down the penetration of moisture and the subsequent gradual widening of the cracks?

[uncl...@ix.netcom.com]

Where do the cross wise cracks and checking come from, based on what you have "heard"?
PU does seal that surface up better, mostly because it seals up the porosity in the gelcoat as well as being a much better UV barrier.
UH

[Dan Marotta]

The paint on my 14 year old LAK-17a looks factory.  No cracking or crazing whatsoever and only a few chips.  I'm a believer!

--
Dan, 5J

[Bob Whelan]

When I apply Occam's razor to gel-coated, commposite gliders, I see relatively
flexible structure beneath relatively brittle gel coat, the latter which -
unsurprisingly, to me - tends to crack. Think chocolate-covered licorice
twists (or some such) - which material's gonna crack first?

The thicker the gelcoat, the more bending strain through its depth, and the
more likely a place for cracking to appear, but I wouldn't bet my life bending
and stiffness are the only contributors. In any event, polyurethane paint now
has a long history of being far more crack-resistant in glider use than every
gel-coat employed to date.

Some years ago, my club sanded one of our G-103's wing-pairs down to the
bottom of its very many (top & bottom/"classic pattern") cracks (because a
glass-inexperienced-annual-guy refused to sign off on it), then had an auto
shop shoot polyurethane. In some places we went down to the glass; in others
we did not. No cracks *into* the glass were found. In the 4 years or so before
we sold the - regularly used in wave - ship, nary a crack reappeared on any
painted surface.

Bob - chief sanding grunt - W.

[son_of_flubber]

On Sunday, November 15, 2015 at 10:23:42 AM UTC-5, uncl...@ix.netcom.com wrote:

> Where do the cross wise cracks and checking come from, based on what you have "heard"?

I've no idea. All I heard was that cracks start in the direction of the final sanding. The person that said it is very well regarded in the glider finishing world.

So does factory PU over factory gel coat delay cracking or have I just been lucky so far? I honestly don't know. I saw a badly trashed gel coat on an east coast only (with no O2 system) glider the other day and it got me wondering what the future holds for my nicely finished Polish factory PU'd wings. We both store our gliders under identical conditions.

[benso...@gmail.com]

> PU does seal that surface up better, mostly because it seals up the porosity in the gelcoat as well as being a much better UV barrier.
> UH

UH...Curious as to the factory steps taken to apply a PU finish. Is everything the same (same gelcoat, same thickness, same sanding, same prep, et cetera sans waxing) then the wing is taken to a paint booth and sprayed like a car?

After spray painting, are the wings sanded or "rubbed" in any way?

What is the current "favorite" maintenance wax or polish for factory finished PU?

Thanks for your response.

[uncl...@ix.netcom.com]

I have not seen a factory production painted glider produced. Andrzej could better comment on this. I do know that the quality of prep before paint needs to be much better than when finishing in gel coat because the paint is much thinner.
I'm sure there is color sanding and polishing.
We protect our painted gliders with Nu Finish glaze which seems to hold up pretty well.
UH

[jpg...@gmail.com]

About 10 years ago when I asked a UK agent/ repairer for one of the major German companies about this I was told that they used thin gelcoat with less white pigment added before spraying with PU on their new gliders. The less pigment the better the polymerisation during curing I was told and colour density wasn't important as it was covered with PU. The gelcoat still looked completely white to me where I could see it under chips and scratches but that's what I was told.

[ND]

On Thursday, November 12, 2015 at 2:15:39 AM UTC-5, Jonathan St. Cloud wrote:

> I was hoping to get a real number, i.e., 5, 10, 15 pounds, from someone with knowledge in this area. Not to be flippant nor disrespectful, but { not enough ... to matter, unless it does matter due to weight of the pilot} while thoughtful is really a null statement.

i apologize if you took my comment as flippant. i meant what i said. i have done 30+ refinishes and its been a mixture of gelcoat and PU refinishes. i do feel strongly that the weight difference is negligible.

Perhaps you can help me by answering why it is of interest to you?

are you close to CG or all up limits?

[ND]

On Sunday, November 15, 2015 at 5:24:23 PM UTC-5, benso...@gmail.com wrote:

I used to work in the paint shop at schempp-hirth.

the two processes are different.

What they do for paint is this: they apply a thin layer of molding gelcoat to the molds. it provides excellent adhesion to the composites, and releases from the mold nicely. when the fuse/wing/whatever is pulled from the mold, the thin layer of molding gel-coat is scuffed with sandpaper. at that point they then spray urethane primer, wetsand it, then do a PU topcoat, wetsand it. then its ready for trim stripes/ decals and polishing. after any striping, they also offer clearcoat to remove the lip edge of any decals/contest letters et cetera. but that's only applied in the local area of the decal.

With gelcoat, after the mold they just spray gelcoat onto the scuffed molding gelcoat.

[benso...@gmail.com]

> > Thanks for your response.
>
> I used to work in the paint shop at schempp-hirth.
>
> the two processes are different.
>
> What they do for paint is this: they apply a thin layer of molding gelcoat to the molds. it provides excellent adhesion to the composites, and releases from the mold nicely. when the fuse/wing/whatever is pulled from the mold, the thin layer of molding gel-coat is scuffed with sandpaper. at that point they then spray urethane primer, wetsand it, then do a PU topcoat, wetsand it. then its ready for trim stripes/ decals and polishing. after any striping, they also offer clearcoat to remove the lip edge of any decals/contest letters et cetera. but that's only applied in the local area of the decal.
>
> With gelcoat, after the mold they just spray gelcoat onto the scuffed molding gelcoat.

Good to know...thanks ND.

[Papa3]

How thick do you recon they get the PU topcoat? I know the PPG Concept we've use recommends two wet coats of 3 mils each for a total of 6 (this is for their standard auto applications). This then dries to a very thin (1-1.5 mils). We were able to get thicker coats for maybe 8-9 mil wet which seemed to give us (barely) enough material to color sand (wet sand). The automotive guy who did the Urethane paint couldn't understand why in the world we'd want to mess up his perfectly good spray job (with only very minor orange peel) by sanding!

As a sidebar... now that I've messed with this stuff, I can't help but look carefully at every car I see in the parking lot. I was looking at a Mercedes GLK the other day which had what glider guys would consider "bad" orange peel on a factory finish. On the other hand, from a work perspective, it's much more efficient to just "spray and forget it".

p3

[robf...@gmail.com]

I've just sanded away the old gelcoat off the wings of my 1978 LS3. I've noticed a couple interesting patterns regarding the gel coat crazing.

a) All crazing stopped abruptly at the edge of any covered portion of the wings gel coat. So for example, the gel coat that was covered by turbulator tape and Mylar tape was perfectly free of any crazing. The crazing lines dead ended at the boundary.

What this means to me, is that at least some portion of crazing is due to evaporation/drying/degradation over time of an exposed critical gel coat chemical. I imagine that some organic molecule embedded in the gel-coat composition over time breaks up and likes to go float around in the atmosphere. I know it is not the sun or UV causing breakup because the bottom surfaces of the wing and stab presented the same patterns and the same amount of crazing.

b) All crazing lines followed an underlying surface defect or discontinuity. For example in my wings, stab, and fuse they followed previous sanding patterns perfectly. This makes sense as the deepest sanding gouges would naturally have the greatest density of exposed surface area and thus degrade the fastest. Or so my theory goes. Interestingly enough there was a perfect craze line that matched the exact pattern of the underside original owners initials that where painted on the wing, JB.

c) The crazing extended to the contact layer of the fiberglass/epoxy layer leaving visible troughs. This very thin contact layer was a distinct material between the gel coat and the fiberglass and was the yellow color of vanilla ice cream. I have no clue what this material is, although Dave Nelson suggested it could be the remaining layer of a previous gel coat. I also thought it could be the "Warning Colour" material called out in the LS3 Maintenance manual as:
Nitro Cellulose Kombilack Reinorange RAL 2004 made by Lackfabrik Bader on page 13.9.

Despite looking extensively through a jewelers magnifying glass I saw no evidence of the crazing cracks extending into the fiberglass matrix.

The only caveat is that Rolladen Schneider used a sandwich structure for the wings and stab skins on the LS3. Not sure if this is true for other sailplane manufacturers. I noticed the outer stab skin is very very thin and can be easily sanded into if you're not careful. According to the maintenance manual, the outer layer of the sandwich has only two layers.

I'd appreciate if you could comment on my findings/theory. One thing for sure, is that I could not identify a single crazing line on my LS3 that was due to mechanical stress or skin shearing like you typically find on the corners of the spoiler box on a Grob. I have some good pictures I'll post.

Roberto

[Craig Funston]

The "warning color" is red - orange lacquer that's used as anti-collision markings.

[Papa3]

There is typically filler along the leading edges where the two halves of the wing were joined. Also, your particular LS3 had some profiling work done in the area of the spar; is that where this additional material was found?

Currently have a 1984 LS4 on the operating table...

p3

[uncl...@ix.netcom.com]

On Monday, November 16, 2015 at 9:53:30 PM UTC-5, robf...@gmail.com wrote:
> On Sunday, November 15, 2015 at 6:17:38 AM UTC-7, son_of_flubber wrote:
> > On Sunday, November 15, 2015 at 4:34:23 AM UTC-5, Paul Crabb wrote:
> >
> > > PU or Acrylic topcoat paint is just used as a very thin UV block, it is usually a very thin layer and is not used to "profile" the surface.
> >
> > Does the PU protect the gelcoat from temperature related crazing?
> > Someone told me that gelcoat crazing was attributed to rapid change in temperature associated with flying wave. Once the cracks start moisture penetrates and accelerates the deterioration.
> >
> > Anyone have a crazed PU painted wing?

Comment- Yep- where painting was done over surfaces where all compromised gelcoat was not removed and surface simply filled.

> >
> > Anyone have a better explanation for wing crazing?
>
> I've just sanded away the old gelcoat off the wings of my 1978 LS3. I've noticed a couple interesting patterns regarding the gel coat crazing.
>
> a) All crazing stopped abruptly at the edge of any covered portion of the wings gel coat. So for example, the gel coat that was covered by turbulator tape and Mylar tape was perfectly free of any crazing. The crazing lines dead ended at the boundary.

Comment- Over coating, such as number painting, seals the surface and pretty much stops degradation.

>
> What this means to me, is that at least some portion of crazing is due to evaporation/drying/degradation over time of an exposed critical gel coat chemical. I imagine that some organic molecule embedded in the gel-coat composition over time breaks up and likes to go float around in the atmosphere. I know it is not the sun or UV causing breakup because the bottom surfaces of the wing and stab presented the same patterns and the same amount of crazing.
>
> b) All crazing lines followed an underlying surface defect or discontinuity. For example in my wings, stab, and fuse they followed previous sanding patterns perfectly. This makes sense as the deepest sanding gouges would naturally have the greatest density of exposed surface area and thus degrade the fastest. Or so my theory goes. Interestingly enough there was a perfect craze line that matched the exact pattern of the underside original owners initials that where painted on the wing, JB.

Comment- This is why finish sanding needs to be very well done so as to not leave deep scratches which are initiation points for moisture, UV, and mechanical stress.

>
> c) The crazing extended to the contact layer of the fiberglass/epoxy layer leaving visible troughs. This very thin contact layer was a distinct material between the gel coat and the fiberglass and was the yellow color of vanilla ice cream. I have no clue what this material is, although Dave Nelson suggested it could be the remaining layer of a previous gel coat. I also thought it could be the "Warning Colour" material called out in the LS3 Maintenance manual as:
> Nitro Cellulose Kombilack Reinorange RAL 2004 made by Lackfabrik Bader on page 13.9.

Comment- This is likely to be a change in the surface characteristics of the gelcoat where the epoxy for laminating was applied wet on wet over the tacky gelcoat. Tis is done to get the best bond between two very different materials.

>
> Despite looking extensively through a jewelers magnifying glass I saw no evidence of the crazing cracks extending into the fiberglass matrix.
>
> The only caveat is that Rolladen Schneider used a sandwich structure for the wings and stab skins on the LS3. Not sure if this is true for other sailplane manufacturers. I noticed the outer stab skin is very very thin and can be easily sanded into if you're not careful. According to the maintenance manual, the outer layer of the sandwich has only two layers.

Comment- Almost all primary surfaces can be expected to be sandwich, except fuselages which are mostly thick single layer.

>
> I'd appreciate if you could comment on my findings/theory. One thing for sure, is that I could not identify a single crazing line on my LS3 that was due to mechanical stress or skin shearing like you typically find on the corners of the spoiler box on a Grob. I have some good pictures I'll post.
>
> Roberto

Comments inserted above- messy
UH

[Per Carlin]

On Wednesday, November 11, 2015 at 3:15:39 AM UTC+1, Jonathan St. Cloud wrote:
> Any idea how much weight the urethane paint option adds to an 18 meter glider?

I repainted my Ls1 wings last winter. I removed about 10kg of gelcote, then did I added about 6kg of primer and PU-paint.

Regarding the odd color on the LS3, I had the same on my LS1. On the first LS-gliders was the gelcote and fiberglas laid wet-on-wet, which made the gelcote and epoxy to be mixed. That mixture has an cream/yellow color and penetrates into the first layer of firbeglass. Do not grind though this as it would genereate a lot of extra work by adding a new layer of firbreglas.

[herbk...@gmail.com]

Gelcoat seems to be holding up very well under vinyl stickers and paint that blocks sunlight as well as O2. This is very evident on gliders as well as trailers and has been commented on in this thread. What do you all think about using white vinyl used for application on cars (self adhesive, heat shrinkable). This would be a much quicker way to protect crazed surfaces. I'd be reluctant to apply these to the wings because of the inevitable joints between the up to 5' wide strips. Cost is a fraction of refinishing in either gel-coat or PU, weight is nearly negligible.
Herb, J7

[Craig Funston]

It's already being done successfully in the power market. http://www.planevinyl.com/index.php

[robf...@gmail.com]

Thanks, between your answer and that of UH, I think my question regarding the odd contact layer has been put to bed. I didn't realize that the fiberglass was layered into the mold on top of wet Gel.

I still haven't made a decision on brand of primer and PU paint to use. I'm curious to know what you used. Regarding the PU paint, there seems to be a consensus on PPG Concept, but it is absurdly expensive around here ($450 a gallon. Regarding the primer, I've seen many mentions of "PCL polyprimer" and on the car business side of things "Evercoat Slick Sand".

[Dan Marotta]

Interesting idea, Herb.  Maybe you could get that 5' width vinyl in a 25' (or more) length. :-)

--
Dan, 5J

[chip.b...@gmail.com]

It's great to hear that my old LS-3 is being rejuvenated with such care! A few words of explanation.

AFAIK, that's the original gel coat. I owned it from 1978 through 1992 and I don't believe there has been a refinish job in the interim.

<All crazing lines followed an underlying surface defect or discontinuity. For example in my wings, stab, and fuse they followed previous sanding patterns perfectly. >

Not sure about this one. I contoured the wings twice and profiled the top surface once. All sanding was done at 45 degrees. After the first three years they were generally left at 400 grit, unwaxed, so rain would spread rather than bead up. Roberto, were the crazing lines at 45 degrees? The wings had crazed hardly at all when I sold it, and I often wondered if that was because the gel coat was likely much thinner and less brittle than when it was new due to the three cycles of sanding/smoothing. I did sand with much finer grit to remove sanding marks, polish, and wax the wings the year before I sold it.

Neither the fuselage nor the stab was ever sanded post factory, to my knowledge. When new they were a high gloss so I'm wondering what the "previous sanding patterns" were. The only significant crazing evident when I sold it was on the filler at the tips of the stab, IIRC.

When I sold it, I changed the registration # and contest ID for the new owner, converting JB into JE in both cases with some rubbing compound. At that time, I also was startled to find perfect gel coat underneath the paint.

< Interestingly enough there was a perfect craze line that matched the exact pattern of the underside original owners initials that where painted on the wing, JB.>

IIRC, the contest ID and registration # on the vertical fin were both scribed around with some kind of sharp tool at the factory, I guess to prevent paint from creeping under? I didn't discover the scribe marks until I polished off parts of the JB. They proved impossible to remove without sanding (which I didn't do). I can't recall if the contest ID under the wing was applied using the same technique but I wouldn't be surprised. That could explain the cracks.

When I bought my ASW 24, I'd already heard of one glider that had been sprayed with paint when new to protect the gel coat. But the LS-3 wings had shrunk over the spar caps so significantly in the first few years that we had to build up the surface with gel coat when profiling them. As a result, I didn't consider painting my new ASW 24. Those wings, however, have been marvelously stable, apparently due to different construction techniques. I've been told the ASW 26 and 24 were built differently than subsequent models (e.g., ASW 27) and are quite stable, though more expensive to build.

Chip Bearden
ASW 24 "JB"
U.S.A.

[robf...@gmail.com]

I uploaded the pictures of the sanding. Let me know what you think of the criss-cross patterns. Quite intriguing. If you can, download the full resolution pictures of the wing reflecting the setting sun (The ones with the pocket knife). You can see the crazing troughs in some of the remaining contact material. The link is: https://picasaweb.google.com/111076367331310539688/LS3Refinish?authkey=Gv1sRgCKeDoqXAyfGiqwE

Roberto

[ND]

welcome to my world. orange peel will be my death at last. i see it on everything.

[Casey Cox]

. You can see the crazing troughs in some of the remaining contact material. The link is: https://picasaweb.google.com/111076367331310539688/LS3Refinish?authkey=Gv1sRgCKeDoqXAyfGiqwE
>
> Roberto

Is that crazing or cloth weave?

[uncl...@ix.netcom.com]

Orange peel and grey shadows. As one goes, other comes.
Gloom
UH

[uncl...@ix.netcom.com]

Crazing associated with total finish failure.
UH

[BruceGreeff]

Modern cars finish is all some degree of orange peel.

It uses a lot of very expensive paint to block and finish an entire
glider to a zero imperfection state. Did I mention the days and days of
patient marker coat eradication...

But it DOES look pretty when you are done.

--
Bruce Greeff
T59D #1771