Mold release info needed for casting fiberglass on plaster mold
Carl Kelly
I am trying to build three fiberglass kayak seats from a plaster of
paris mold, and am seeking info on mold release compounds. At this
point, I have a nice mold, but my first experiments with some test
molds have failed to release satisfactorily.
So far, I have tried creating a plaster mold of a bowl, saturating the
surface of the plaster with paraffin by using a heat gun, then rubbing
additional paraffin on top of the mold - the mold could only be
removed by breaking it out in chunks.
I have also tried painting the plaster (to seal it), then applying
liquid automotive wax. In this case, the release was somewhat better,
but the paint stuck to the fiberglass part.
I have a mail order catalog with 'part all' mold release agent and
'part all' base wax. Can anyone tell me if this will work over
plaster? Should I paint the mold first? Should I consider coating
the plaster mold with resin and finishing it out before applying a
mold release?
Any advice would be greatly appreciated!
Paul Mathews
.....
>
> >I am trying to build three fiberglass kayak seats from a plaster of
Silicone mold release compounds are available in spray cans at tooling
supply houses and plastics supply wholesalers.
--
Paul Mathews, consulting engineer
AEngineering Co.
opt...@whidbey.com
non-contact sensing and optoelectronics specialists
Paul Stomski
Carl Kelly wrote:
>
> I am trying to build three fiberglass kayak seats from a plaster of
> point, I have a nice mold, but my first experiments with some test
> molds have failed to release satisfactorily.
>
In Charles Walbridge's Book "BoatBuilders Manual" he suggests using a
high carnuba content hard paste wax. And he specifically states to
avoid an wax containing silicones. He suggests 4-5 coats initially on a
mold and 2-3 before each new use. For each coat, allow wax to dry and
buff. Do all waxing by hand, Walbridge says that power tools heat/melt
the wax, and cause invisible gaps.
I've used this approach on a wooden mold for small parts (10 inches X 3
inches), and it worked good. I actually started adding one extra layer
of paste wax just before layup, without buffing or even allowing it to
dry. It worked good, whether it was necessary or not, who knows!? Only
when I got lazy or sloppy did I have any problems with sticking.
Paul
Project Status: "Cedar Strip Sit on top Kayak"
Working on cutting the station molds, last night, tried using a belt
sander option on my band saw to take a rough cut form 'down to the
line". Worked well.
Chuck Holcomb
kel...@execpc.com (Carl Kelly) wrote:
>I am trying to build three fiberglass kayak seats from a plaster of
>paris mold, and am seeking info on mold release compounds. At this
>point, I have a nice mold, but my first experiments with some test
>molds have failed to release satisfactorily.
Experiment with these three substances:
Talc
Vaseline
Motor oil
-
Chuck Holcomb
chu...@netheaven.com
+
The Second Amendment is in case the government ignores the First...
+
Don Ford
kel...@execpc.com (Carl Kelly) wrote:
>I am trying to build three fiberglass kayak seats from a plaster of
>paris mold, and am seeking info on mold release compounds. At this
>point, I have a nice mold, but my first experiments with some test
>molds have failed to release satisfactorily.
I would recommend painting the mold first, better yet coat with epoxy
resin and let it dry good.
I would then use a wax formulated as a mold release wax (many auto
type waxs are not suiltable). I would also use PVA liquid. This is
the standard process on boat molds and shoulkd work with your mold.
Good Luck
Don Ford
Steve Weingart
In article <512dp9$g...@tofu.alt.net>,
chu...@netheaven.com (Chuck Holcomb) wrote:
>kel...@execpc.com (Carl Kelly) wrote:
>
>>I am trying to build three fiberglass kayak seats from a plaster of
>>paris mold, and am seeking info on mold release compounds. At this
>>point, I have a nice mold, but my first experiments with some test
>>molds have failed to release satisfactorily.
>
>
>Talc
>Vaseline
>Motor oil
>-
You might also try a commercial mold release agent. Call your local supplier
of fiberglass materials. Mistakes are costly for this one
Steve
David Knaul
kel...@execpc.com (Carl Kelly) wrote:
>I am trying to build three fiberglass kayak seats from a plaster of
>paris mold, and am seeking info on mold release compounds. At this
>point, I have a nice mold, but my first experiments with some test
>molds have failed to release satisfactorily.
First make sure the plaster is completely dry. Paint the mold with a
coat or two of epoxy to fill any porosity in the surface. When that is
cured, cover with several coats of paste wax. There are special mold
release formulations, but for just a few parts, the stuff for finishing
wood should will be fine. If you are still having problems, spray over
the wax with PVA (polyvinyl alcohol) mold release compound.
Dave Knaul
kn...@andrew.cmu.edu
Michael Weiner
Don Ford wrote:
>
> kel...@execpc.com (Carl Kelly) wrote:
>
> >I am trying to build three fiberglass kayak seats from a plaster of
> >paris mold, and am seeking info on mold release compounds. At this
> >point, I have a nice mold, but my first experiments with some test
> >molds have failed to release satisfactorily.
>
> resin and let it dry good.
> I would then use a wax formulated as a mold release wax (many auto
> type waxs are not suiltable). I would also use PVA liquid. This is
> the standard process on boat molds and shoulkd work with your mold.
>
> Good Luck
> Don Ford
I have also had great success mixing the PVA with epoxy and applying the
mixture as a gel coat to the mold. The ratio is about three tablespoons
of PVA (green liquid form) to about a cup of mixed resin. Mix well, and
apply with a spatula or squeegy. Once the gelcoat dries, wipe the
surface with a clean wet towel (wet with water only). The removes the
PVA from the suface of the gelcoat to allow your laminant on top. The
wax we use is a Carnuba wax that is specially made for mold release.
A.C. spruce or Gougeon bros. should have it.
A word of caution howevever, we always double up on our mold release
techniques. That is, we still wax and polish the mold three times, and
then use the PVA gelcoat on top of that surface.
I have yet to see this technique fail on epoxy molds, but I have pulled
some paint off of a painted mold.
Mike.
**********************************************************
Michael Weiner
Graduate Student
Colorado State University
bere...@caent11.esa.lanl.gov
>I am trying to build three fiberglass kayak seats from a plaster of
>paris mold, and am seeking info on mold release compounds. At this
>point, I have a nice mold, but my first experiments with some test
>molds have failed to release satisfactorily.
The recommendations to paint with epoxy and then wax and/or PVA are
all good. If you can heat the mold, then solid Carnuba wax works
well. Heat the mold hot enough to melt the wax, apply the wax, let it
cook for a while, then wipe off the excess. This gets the wax into
any pores. Whatever method you use, reapply the release before laying
up each new part.
However, ignore the suggestions to use talc, vaseline, motor oil, or
silicone spray. All of these will contaminate the resin (yes, even
silicone spray).
--
Barry Berenberg
Los Alamos National Laboratory
ESA-DE
bere...@lanl.gov
Garfield
Silicone release alert!!
Just be aware that if you ever use this on ANY mold, you're stuck with
it on that mold from thence. Once you have used silicone release agents,
you can't effectively use wax/PVA after it. The reverse is not true.
Also, since it is nearly impossible to solvent off, you really want to
avoid it if the part is to have pieces/tabs/whatever lam'ed to it later.
Wax can be removed easily, and PVA can be washed off, but silicone is
forever, sorta.
Garfield
thomas a.decker
On Sun, 08 Sep 1996 15:56:14 GMT, kel...@execpc.com (Carl Kelly)
wrote:
.
>
>I have also tried painting the plaster (to seal it), then applying
>liquid automotive wax. In this case, the release was somewhat better,
>but the paint stuck to the fiberglass part.
>
>I have a mail order catalog with 'part all' mold release agent and
>'part all' base wax. Can anyone tell me if this will work over
>plaster? Should I paint the mold first? Should I consider coating
>the plaster mold with resin and finishing it out before applying a
>mold release?
>
>Any advice would be greatly appreciated!
>
I have used the "part all " agents and had good luck with them . For
the mold I also used plaster , paint , I just used enamel paint it
works . But be sure to let the plaster dry for a few days , it holds
water very well . spray the paint and let it also dry a couple of days
also ( you can recoat as soon as the the paint instruction say then
let it dry the two days ) wet sand with 600 grit wet dry paper
between each coat . Then follow the " part all " instructions .
When you go to remove the part try using compressed air to help break
the suction between the part and mold . Good luck and have fun .
....Regards Tom Decker
tde...@spectra.net
COUGER GORDON
I have used a couple of coats of shelac and 4 coats of Johnsons wax with good
results. There may be better stuff but my grandmother showed my this in the
early '50s and it has worked ever since. We wern't doing fiberglass at the
time but I have used it for that.
Good luck
Gordon
In article <ug24pt...@caent11.esa.lanl.gov>,
Gordon Couger Senior Software Specialist
Biosystems & Agricultural Engineering Dept. Oklahoma State Univ.
114 Ag Hall Stillwater, OK 74075
gco...@master.ceat.okstate.edu
Judy Anderson
Lots of people have responded to this, but it's being cross-posted
inappropriately. Please edit the headers.
Many thanks.
Neal Nicholson
Someone in an earlier post recommended a company called Fibreglast. I
have purchased their videos on mold making and vacuum bagging and found
them to be very informative. I'm still in the process of building my
plug so I have not had any experience with the molding process. They
have a web sight and you can request a free catalog.
Basically they recommend painting the plug then filling any pin holes in
the paint then painting again followed by wet sanding and polishing.
Then just before you begin to lay up the mold you put on 6 coats of a
parting wax followed by 2 coats of PVA.
Let us know how you make out
Neal
Pete Hodgins
This isn't about the parting problem, but if you're trying to
produce a plug or mould that's both smooth and fair, you may need MANY
iterations of paint-fill-sand before you've perfected the surface.
I use various contrasting colours of paint, so that sanding shows
clear contrasts between high and low areas. Pits & pinholes show up
clearly, at the same time; they should be remedied with body filler if
they're at all big, because building up paint layers to fill them may take
forever and a day. It's essential to use long sanding blocks or battens
held generally in the fore-and-aft direction, and to have them in a
variety of shapes to fit concave root fairings, etc.
Only when minute inspection reveals no further problems is it time
to begin the mould-release system.
Someone has said the headers for these articles are wrong. I guess
that means this thread should appear only under rec.boats.building. So be
it, but I hope someone out there wants to do the transferring. While the
thread exists under rec.boats.cruising, we're likely to discuss it where
we find it.
Pete Hodgins, Sr.
Pete Hodgins
Don Ford (df...@auburn.campus.mci.net) writes:
> kel...@execpc.com (Carl Kelly) wrote:
>
>>I am trying to build three fiberglass kayak seats from a plaster of
>>paris mold, and am seeking info on mold release compounds. At this
>>point, I have a nice mold, but my first experiments with some test
>>molds have failed to release satisfactorily.
>
> I would recommend painting the mold first, better yet coat with epoxy
> resin and let it dry good.
> I would then use a wax formulated as a mold release wax (many auto
> type waxs are not suiltable). I would also use PVA liquid. This is
> the standard process on boat molds and shoulkd work with your mold.
>
> Good Luck
> Don Ford
Wish I could remember how I did it with plaster moulds for
replacement hub spinners for my 1958(?) Berkeley [pronounced Barkley, in
England] sportscar's wheels. The insight is gone the way of much ancient
history, though ...
Because of solvent attack, not every paint works well. I've
settled on a hard, outdoor oil-base type that acts like `virtual gelcoat'
when allowed to cure at least a day. For moulds carved from Styrofoam or
other foamed polystyrenes, though, it's advisable to begin with several
coats of water-based outdoor paint, to avoid dissolving the plastic. Note
also that fiberglassing resins attack polystyrenes, which have to be very
well coated for protection against them.
Recently, I built and nicely waxed some fibreglass moulds, partly
painted, as mentioned, during the fine-finishing stage - but then found I
couldn't satisfactorily coat them with polyvinyl acetate (PVA) liquid. At
whatever the spray setting using a Wagner non-air-blast electric gun, the
stuff beaded. I then tried brushing, which often leaves brush marks - and
it still beaded. I got the surface as smooth as I could and went ahead
with the layup, then sanded out the resulting irregularities after
separating the pieces with only moderate trouble.
Thank goodness my object was a set of one-off corrective fairings,
to be incorporated into a prototype boat. From the latter, production
moulds may or may not be cast, depending on the modified prototype's
success during sea trials, and on my own meagre marketing ability. In
other words, I pass on to some imaginary production builder the problem of
assuring smooth surfaces in future copies, if any.
Any comments on how to combat the beading fault, while adding PVA
over wax, would be appreciated. Someone's idea of mixing PVA into an epoxy
coat intrigues me. Would that make a later PVA coating adhere more smooth-
ly, I wonder? The problem seems to be, a wax layer is then interposed. If
you'll pardon a Shakespearian pun, "Aye, that's the rub."
BTW, my project is a microcruising catamaran, with a potential
backup use as an electric boat. By chance, a builder of the latter sort of
craft has set up near our home, and he's academically interested. The high
drag hull he now builds is slow and sales are poor, though, inhibiting new
ventures.
Marketing is always the big problem for a smalltime designer, in
the end. It can be tougher than coming up with good products. It's 'way
tougher than finishing moulds, I find.
Pete Hodgins Sr.,
aw...@frenet.carleton.ca
scotttrav...@gmail.com
> I am trying to build three fiberglass kayak seats from a plaster of
> paris mold, and am seeking info on mold release compounds. At this
> point, I have a nice mold, but my first experiments with some test
> molds have failed to release satisfactorily.
>
> surface of the plaster with paraffin by using a heat gun, then rubbing
> additional paraffin on top of the mold - the mold could only be
> removed by breaking it out in chunks.
>
> liquid automotive wax. In this case, the release was somewhat better,
> but the paint stuck to the fiberglass part.
>
> I have a mail order catalog with 'part all' mold release agent and
> 'part all' base wax. Can anyone tell me if this will work over
> plaster? Should I paint the mold first? Should I consider coating
> the plaster mold with resin and finishing it out before applying a
> mold release?
>
> Any advice would be greatly appreciated!
brucein...@nowhere.org
surfaces of the mold with an epoxy paint and then sand all the
imperfections out of the mold until the surface is shinny, which may
require re-painting a number of times. Then they coat
e the mold with commercial mold release, see:
http://www.mann-release.com/prodgude.htm
for details.
Two things to note:
(1) the mold must be made to incorporate "draft". See
https://en.wikipedia.org/wiki/Sand_casting
" A slight taper, known as draft, must be used on surfaces
perpendicular to the parting line, in order to be able to remove the
pattern from the mold. This requirement also applies to cores, as they
must be removed from the core box in which they are formed".
(2) a really well made casting is held into a perfectly made mold by
air pressure, i.e., about 14 psi, which must be overcome in some
manner to remove the newly cast part. I.e., a 6 by 8 inch part
requires (6 x 8) x 14 = 672 pounds of force to pull it directly out of
thus mold, unless it can be "peeled" out of the mold.
--
Cheers,
Bruce
