Mold release problems.....
 

Hi, I have made many molds for my planes.I just finished one and just can'e get it to release!I finially had to break the mold to get the piece out. I use TR Industries mold release to wax the mold, about eight coats. Then I sprayed with my airbrush, three coats of mold release called PVA 360, a green colored agent. I waited till it was dry, about two-three hours before I put the first coat of expoxy , about a hour later I glassed the mold with two layers of 6 oz. glass. What is the problem here????? Am I useing the wrong release agent? Thanks for any help. The mold has a nice shiny interior, five coats of white laqure,buffed out smooth.

RE: Mold release problems.....
 

if you didn't let that lacquer cure completely (can take up to 30 days) then there is your problem, I've had lacquer stick many times when i got in a hurry :(

RE: Mold release problems.....
 

I am inclined to agree with that. I have never used "Paint" of any sort as the mold surface. I always us an epoxy gelcoat. I make the gelcoat from the resin and graphite powder. The result is a hard glossy surface.

Ed S

RE: Mold release problems.....
 

First of all, I have nev er painted a mold before, but that shouln't matter, if it is thouroghly waxed over.  The problem I think is that PVA has a solvent that keeps the mold release in a liquid state, untill it is sprayed or painted onto a surface.  Then the solvent evaporates and leaves behind it the green mold release film.  If you are applying this solvent onto a previously waxed mold, the solvent will liquify the wax mold release underneath it and you will have a chaotic mold release situation.  Stick with one or the other, and that should do it.  I noticed you mentioned a coat of epoxy before glassing.  Very good.  Polyester has solvent that breaks down wax mold release.  This first coat of epoxy; is it sprayed or brushed? PVA is basically a very thin layer of wax.  It can be broken easily by a sqeegee or even a brush.  Make sure this first coat of epoxy is sprayed on delicately.  Give the epoxy plenty of time to completey cure before glassing over it.

RE: Mold release problems.....
 

Lou,

I'm sorry but I have to disagree.

While WAX can be used alone, PVA NEEDS to be used on top of wax. It will not melt the wax if a proper molding wax is used, like partall number ten paste wax (greenish blue).

Also, polyester will NOT melt molding wax. I made a polyester mold two weeks ago using only molding wax, no PVA.

Also, PVA is not a wax. It is a plastic film-like barrier that protects the reactive mold surface from epoxy. It is applied with an airbrush, left to dry, and when the part is released (full cure), it can be peeled off in a film (like saran wrap) or washed off with warm water.

Also, if you apply a coat of epoxy (no reinforcement), you should apply the reinforcement when this coat is STILL TACKY, to form a better chemical bond. If you wait for full cure, the prescence of amine residues will make the bond weaker, and it will be purely mechanical and not a chemical bond.

OH, and for molds, I use a polyester gelcoat, thickened using fumed silica (aerosil or cab-o-sil) and tinted with red ochre powder.

Have fun!

RE: Mold release problems.....
 

I have used catalyzed automotive paints with good results. I have used spray can enamel and lacquer, each only once, and each with disastrous results.