Working with styrofoam!?!?!?

[OdiWan72]

Hi all

Inspired by the great results (armor, helmets and more) clonesix and others had with styrofoam, I got myself some blocks of a similar high density foam here in Germany...

I don´t have a problem working with it as far as cutting, shaping, sanding etc.
BUT I don´t have a clue how to prepare this stuff for molding. :unsure

Can I simply put LOTS of coats of sandable primer on the foam to "seal" it ?
How can I sand a primered/ puttied surface without leaving impressions in the master?
What else do I have to pay attention of before brushing silicone onto the master?

Many thanks in advance, Markus

 

[takevin]

. Yes depending on the foam, a couple of coats of sandable primer will be all you need, sand in between coats.

 

[Lord_Gita]

Depends greatly on the foam. I'm not sure abotu your high density foam but some types of will melt under aerosol paints. Leaves a nice effect but not likely the effect you're looking for in this case.

Simple way to find out, take a small pile of waste material and spray it. If it melts, try something else.

Another idea is to seal with wood glue and then smooth out the surface with bondo. But that can lead to a great deal more if the detail is already sculpted and also can make the piece a bit larger with the thickness of the glue and bondo, so if size accuracy is an issue either compensate first or find another way...

 

[Honus]

A great way to finish foam is to first sand it (use about a 400 paper and wipe it down with a soft damp cloth) and fill in any pits/defects with a lightweight spackling putty and then lightly sand it again with a very fine sandpaper. Then get some silkspan (the stuff used for covering model airplane wings- places like Tower Hobbies sells rolls of it) or very light weight fiberglass cloth and cover the foam with Minwax Polycrylic. Make sure the covering is completely wetted out with the Polycrylic. Once it dries it can be sanded smooth and painted with most all types of paint without worrying about dinging the foam or melting it with the paint.

It's basically a cheap and quick method of low cost fiberglassing without the mess and smell.

 

[Aegis159]

<div class='quotetop'>(Honus @ Sep 3 2006, 12:52 AM) [snapback]1312112[/snapback]</div>

A great way to finish foam is to first sand it (use about a 400 paper and wipe it down with a soft damp cloth) and fill in any pits/defects with a lightweight spackling putty and then lightly sand it again with a very fine sandpaper. Then get some silkspan (the stuff used for covering model airplane wings- places like Tower Hobbies sells rolls of it) or very light weight fiberglass cloth and cover the foam with Minwax Polycrylic. Make sure the covering is completely wetted out with the Polycrylic. Once it dries it can be sanded smooth and painted with most all types of paint without worrying about dinging the foam or melting it with the paint.

It's basically a cheap and quick method of low cost fiberglassing without the mess and smell.
[/b]

You don't have to use the cloth if you first cover the foam in the lightweight filler. I've used the filler as a base to protect foam RC aircraft from the highly corrosive nitromethane fuel. Granted I sprayed a fuelproof paint over the filler, but the paint had no issues with the foam once it was covered with the filler....

 

[Honus]

Was it still good at resisting dings without using fabric reinforcement?

 

[REL]

Without the fiberglass cloth it'll ding pretty easily. Depending on the type of foam you can either seal it off with spackle or joint compound like was suggested, or bondo, test a small spot first because bondo might eat the foam.

 

[OdiWan72]

Many thanks for your advices ...

I´ll give it a try shortly

Markus