I'm working on a project for my house and have made an exact model of a form i want to make from fiberglass.....i have carved it out of the dense pink house foam that come in 4x8 sheets as it was easiest to form and carve to what i wanted it to look like. Now the question is....what do i use to cover this to make it smooth so i can cast a mold from this and start to make a fiberglass model of it?? My concern is if i use too harsh a chemical or what have you the foam will melt. I'm thinking maybe a light layer of bondo??? then cover with a gelcoat and sand smooth???

Thanks in advance!

Sounds to me like your on the right path. It should work fine with bondo and gel coat. Just be sure to wax the gel about fifteen times before glassing the mold.

the foam will probably not like bondo or any polyester resin based filler on it. i have never used foam for a plug but if it is dense and rigid enough you might try some kind of plaster (crude an fast if its a one shot deal) might not sand to badly either. coat that with PVA and pull a mold from there. i would also use PVA for the mold release when you go to make the actual part, it will keep you out of trouble like cookin the part in the mold.

btw, what are you building? just curious

make sure you use an expoxy resin. regular polyester resin A. STINKS like ass b. will met that foam

Puder is a 100% Right you will have to go the epoxy route..

OK, so i go the epoxy route......and when glassdave mentioned plaster i had an idea of useing some left over drywall plaster! i will test it on a left over scrap piece of foam i have to see how it will react. The stuff i have is sooo nice to sand it almost melts right off!

PVA??? what is it? i have been reasearching this whole mold thing for a little while now and have heard that term before but never explained.....i have read of useing a few coats of a heavy car wax like Meguires or such...but what is PVA and where do i get it?

and as for what i'm building.....when i moved into my house the furnace humidifier had a fiberglass cover on it that was cracked and broken.....i threw it out like an idiot thinking i could make one from sheet metal or something......made one but it looks like ass cause i cant match the nice curves it had, so now i'm doing the original type route....

Thanks guys....any other suggestions or advice for me?

Mequires also makes a Mold release wax... find it at a Paint Supply store for around 7 bucks.

cool thanks...we actually use a mold release spray here at work...but the stuff looks "lumpy or wavy" when its sprayed into the mold for our epoxy encapsulted pumps....leaves an orange peel texture on it i dont want.

For the fairing it out I would use Epoxy Resin with West systems fairing compound. The higher the number for the west system the easier it is to sand. Once you have htat you will be all set to make your mold or part. Another option is to just put the glass on top of what you have then pour accetone into the thing after the resine cures to melt away the foam. That is only if you need one of the things.

Jon

Audio, the acetone thing would work great if my foam core was absolutly perfect! but it not and fairing will be needed. Thanks for the west system advice!