making FG parts - Casting material help

[don911]

I'm making some 964RS style splitters for my 930S valance. I have the shape on the car and am making a mold of the shape out of plaster. I want to then cast the shape so I have a plug that I can then use to make the FG or CF part.

Any ideas on casting material? Michaels sells "art plaster" that I'm thinking of using but don't know how it will work as a tool. Tap Plastics sells two part casting material but it's expensive for the qty I'll need.

Anyone have experience/suggestions for casting material? Thanks.

[Jagshund]

Never tried the art plaster; I normally use wood for bucks-n-plugs . . . if you seal it well enough I believe it will work. There are others here with much more glass experience that should have a solid answer for you.

[toddc]

Plaster will work for a mold, but it won't have any real strength by itself. It will be dimensionally stable, but don't twist it or heaven forbid drop it...
With any plaster be sure to put it down in multiple layers with hemp or burlap in between for reinforcement.
Have you considered doing a layup using polyester resin and chopped strand fiberglass mat? Much less aggrivation than plaster and much faster to dry, and stronger give the size.

--todd

[stormcrow]

I used fiberglass mat. Spray a thin film of oil on the part to be case, fiberglass over it and pop it off when it cures. You then have the mold to make the fiberglass part.

When making the new part spray the mold again with a thin film of oil and use "cat hair" fiberglass to make the part. That stuff is extermely tough and it can be purchased at any auto parts store.

Steve

"A Porsche does more then just go fast in a straight line.

[don911]

I ended up trying fiberglass but couldn't get the cloth to lay down for a good mold. (see my fiberglass help needed post)

Anyway, yesterday a co-worker told me about this stuff call Duruhms Water Putty. It's powder form and add water. I tried some last night and I think it's going to work great to make the mold and to then make the cast.

[jimmcc]

Originally Posted by don911

Anyway, yesterday a co-worker told me about this stuff call Duruhms Water Putty.

Where did you find this?

thanks

[don911]

oops spelled the name wrong. It's Durhams. I bought it at lowes. The small can was under $3 and the large can was around $8. Here's the website.

Donald Durham Company -- Makers of Durham's Rock Hard Water Putty (tm).

[Kroggers]

Please post some pics after you made the mold with that stuff...

[don911]

Originally Posted by Kroggers

Please post some pics after you made the mold with that stuff...

The Durhams looked good but it was too brittle for a mold. Might have worked if I built it up ALOT but it crack so easily I gave up. I went back to the plaster cast for a mold. I plan on using the Durhams for the casting matial. In a solit lump it should work well... I hope. Here are some pics.

[NY65912]

Durhams is an old time wood filler.

How about using a spray foam? I would cover the splitter with plastic stretch wrap and the spray the foam.

Or, how about using clay?

[bell]

for molds i would always use cloth, then immediately back it with duraglass, use a "mold release wax" (maquires make some) and coat the piece you're molding, let it cure, done......

be carefull separating it, then you can do some detail work to the mold, the key is to always use the release wax or you'll never get them to separate.

when you're making your actual piece from the mold i mix up a batch of 50/50 resin/bondo, this will give you a finish which will be just about ready for primer, then back that with your matting or duraglass.....

i'll be starting some molds for some carrera 924 headlight buckets soon, i'll post a link when i get started.....

[AndrewWolfeUK]

I make grp parts for race and rally cars.
You are pissing in the wind trying to take a mold while the bumper is still on the car, take it off and put it on a bench. Cover area to be copied in mold release wax and buff off. Paint resin or gelcoat over the area and allow to dry but not to cure, while it's still tacky apply another coat of resin and start to apply pieces of chopped strand matting and more resin, pat with a paint brush to remove air pockets. Build it so it's 3mm thick and repeat until it's 6-7mm.
Allow to fully cure and remove, give it a few days and wax up the mold/buff off, you are now ready to make a product, follow same I instructions but only make it 3mm thick in total. Trim the edges to make the product easier to easier from the mold.
Hope this helps.

[proffighter]

Free manual from the leading FG company in Europe:

http://www.swiss-composite.ch/pdf/i-Handbuch-Neu-edition-06-09.pdf

PS: It's in English :-)