When making a mold. if I use a 80g Emulsion Bound CSM as a sealer layer after Gel Coat which needs a polyester resin can I then use 300g Powder Bound CSM with Epoxy Resin for all the remaining layers of the mold? I realize that I can use polyester resin on the powder bound CSM but I would rather use Epoxy even though it is more expensive.

One of the reasons I would like to use epoxy resin is the plug I am building is made out of foam board from the local home depot and I have read that you can seal it with an epoxy resin and not a polyester resin. Does anyone know if this is true? I do know you can't do it with the polyester resin for a fact. I tried it and it ate the foam just like they said it would.

I guess that brings up another question.....Can you put CSM with polyester resin ontop of epoxy resin?

Thanks,

   Dennis G 

Hi Dennis,

if I use a 80g Emulsion Bound CSM as a sealer layer after Gel Coat which needs a polyester resin can I then use 300g Powder Bound CSM with Epoxy Resin for all the remaining layers of the mold?

I would not recommend backing up a polyester or vinylester gelcoat with epoxy resin. Although it will bond to some extent it won't be as good as polyester resin to back-up polyester gel or epoxy resin to back-up epoxy resin.

I realize that I can use polyester resin on the powder bound CSM but I would rather use Epoxy even though it is more expensive.

One of the reasons I would like to use epoxy resin is the plug I am building is made out of foam board from the local home depot and I have read that you can seal it with an epoxy resin and not a polyester resin.

I'm slightly confused by this. If your pattern is made of polystyrene then it's true that you can't 'seal' it with polyester or vinylester resin (or anything else that contains solvents) because they will dissolve the foam. Epoxy would be fine so you can coat the polystyrene foam pattern with epoxy and then flat and polish that ready to pull a mould off. Once you've done that, you would be OK to use either epoxy, polyester or cinylester gelcoat on that pattern as the gelcoat for your mould. Polyester resin will release of epoxy; it's epoxy that won't release off polyester (i.e. if the pattern was coated in polyester, which you've already found you can't do anyway because it will dissolve the foam) where you would have a problem.

From what you're describing you should start by coating the polystyrene foam pattern in epoxy (you might want to add a thin layer of glass as reinforcement too). Flat and polish until you've got the finish you want, then coat in release agent.

Then, you could either:

Use polyester gelcoat followed by polyester resin and emulsion bound chopped strand mat to make the mould.
or/
Use epoxy tooling gelcoat followed by powder bound chopped strand mat and epoxy resin to make the mould.

I hope this helps.

Matt Statham
Easy Composites / Carbon Mods - Technical Sales

Hi Dennis

I use polyester resin over styrofoam all the time. It will melt so you have to seal it. Because it is so cheap and easy to rough shape with a cheese grater file I use it all the time.

Here is the trick. Rough shape and board sand. Now spray a mist coat of 3m contact adhesive. (the 3m stuff will not attack the foam)

Now cover the whole thing with aluminium foil that you need to steal from your wifes kitchen.

Make sure you overlap. I use a small roller to get the aluminium to lay down. I then use packaging tape on the seams.

Yah it doesn't look good and its folded  but it is less than 1/32 thick distortion.

I then put on a few coats of wax. Bing! your done.

Now put one coat of glass matte with the polyester.

When this cures build up all the layers you need, it will not attack the foam.

Often at this point I will do a rough trim and dig all the foam out and mount this mock up to a wood frame.

I then go at it with lots of bondo and sculpt it with a cheese grater file while it is still in the rubber state.

Fred 

Thanks for the responses.....Some good info......I have been doing alot of reading and watching videos.....That may be good and bad...who knows?.....

I was wondering if any one has just painted the foam with a Laytex paint then used dry wall compound over it? I have read that you can seal the foam with the paint then you should be able to go over it with fiberglass. If I read correctly you should be able to use a polyester resin. who knows if that is correct.  I could try it with some scrap pieces to see I guess.

The reason I want to use drywall compound is I have seen a video that the person used it to shape their plug due to it being cheaper than bondo and easier to sand. I like that Idea.

All I want to do is add thickness in some way to my plug so I can finish shape it.  Preferably would like to do it as cheap as possible. I have attached a pic of the tunnel I am going to make. This pic is before I cut and shaped the foam to roughly the shape I want. I made my rough plug 1/8" (3.17mm) under size so I had room to build it up to finished shape.

Fred....Your way sounds fairly easy and cheap I may give this a try.  One question....After you put the foil and tape on why did you wax it? Was it because you wanted to dig the foam out?  If I don't wax it will the Fiberglass stick to the Foil? I would prefer this.

Thanks for the feedback,

                       Dennis

I put the wax on as a guarented barrier. I could also release the foam plug a bit better. But it still sticks real good.

If you want a pro plug you have to go with a hard surface. (in my opinion) You want to treat it like a car body job. The shape has to be perfect but the finish doesn't. Because to get a glass like shiney mold you have to wet sand and polish anyway. A gallon of bondo is less than $20 bucks and goes a long way. Then primer surfacer/ spot putty/ primer surfacer again. Board wet sand/ polish etc make mold.

Fred