Mold release info needed for casting fiberglass on plaster mold

[s***@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.
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!

seal it with Tre Wax,and then use copiuos amounts of PVA liquid mold release.. spray it on, fogging it first, and very slowly build up the mold release until it is very green...then add more! you can also add a bit of clay to your plaster to help it disolve in water.

[b***@nowhere.org]

On Tue, 16 Feb 2016 19:20:16 -0800 (PST),

Post by s***@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.
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!

seal it with Tre Wax,and then use copiuos amounts of PVA liquid mold release.. spray it on, fogging it first, and very slowly build up the mold release until it is very green...then add more! you can also add a bit of clay to your plaster to help it disolve in water.

I've seen boat molds made and essentially they paint the working
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

[Ben Franklin]

I've heard of using automatic transmission fluid for a mold release. Anybody here have any experience with that?