Need help making mold. Ideas?

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#1

I am attempting to make a mold using epoxy resin. The parts I’ll be made from carbon/vacuum infusion. Usually when I’m making a mold I paint the part with cleat and buff. I use Freekote 770- NC and this seems to work fairly well. The problem is the painting is time consuming. Should I just use PVA? Or can I maybe just apply 770-NC directly to the parts since it’s plastic? Looking for a faster way to build my molds. I’m worried that I won’t get the “perfect part” that I’m used to if I use pva. I’ve attacjed photos of the 2 parts I am attempting to make.

#2

I would use PVA. The original parts look like they’re textured so PVA won’t have much effect on the finish anyway. PVA is perfect for this application. It will form a chemical barrier to prevent the resin from reacting with the plastic. It will guarantee a safe release and the original part will still be in perfect condition. If you haven’t used PVA or have had trouble spraying PVA, see a post I made regarding that in Tricks of the Trade, page 4. I recently made molds of parts similar to yours and if I knew then what I know now, I would have used PVA and they would have turned out better and the original parts would still look like new.

#3

Thanks I will try this. Can I use a brush to apply?

#4

You can, but it is far better to spray. I’d suggest looking for a Preval sprayer if you don’t have spray equipment.

#5

Ok going to try and order one. There’s probably a thread somewhere here that explains how to mix it?

#6

No need to mix, can spray it as it is straight out of the bottle.

#7

So don’t thin the pva at all?

#8

No, there’s no need.

If the ambient temperature is very hot, you may find the PVA dries in the air and lands on your part as lumps rather than a film. If that happens then you can add 5% water to the PVA. But otherwise, spray it as is.

#9

If, on the other hand the ambient temperature is cool, or the humidity is high, and the PVA still needs thinning, you can add up to 25% Methylated Spirits.

#10

Methylated spirit goes under the name of de-natured alcohol in USA. Isopropyl alcohol can also be used to thin the pva.