some noob question about starting resin and silicon

[Psygnosis]

Hi all,
I first want to say sorry for my noob question, but I trust you more than any sites I could find on google.
I'd like to start to learn how to make a mould and casting resin on my props.
I never did it because it was a little too expensive, but now after some commission I'm ready to invest on it and learn something new (and honestly I'm pretty excited about it).
but, I have so many doubts:

1. what kind of (cheap if its possible to start) silicone mould I have to buy?
2. what are the materials that I must not use for silicone mould?
   (I work essentially with foam and polystirene/styrofoam)
3. can I resin cast polystirene/styrofoam?
4. is there something that I have to know about the kind of resin? I know that epoxy is the one you use most right?
5. how can I know the measure of resin that I need for a specific mould? in my city I can buy only 500g prochima epoxy!

sorry for my english I don't know some tecnical terms.

 

[krispikarim]

This video series by Bill Doran explains the process of silicone mold making and casting.
https://www.youtube.com/playlist?list=PL6q0fd3ileWLwTQ6pOUb8isS4BYLjkNhH

 

[falloutboy]

I use smooth-on products primarily for mold-making. Oomoo is awesome, easy to use, and lasts a decent time.

Their resins are great as well- I've used their TASK series and Smooth-Cast urethane resins.
Alumilite makes some resins that fill the gaps that Smooth-On leaves, in my opinion.
Smooth-on's stuff can be used without vaccum or pressure chambers often without bubbles- which is nice.

Mold box material of choice for me is Legos! They work awesome to create a custom sized box of your choice.
I use simple Vaseline when pouring my multi-part mold sections, and a pen cap or marbles for my keys. Usually the caps anymore.

Mold making can be awesome- and easier to get into then people think.
My next items of purchase will likely be a vacuum chamber and pressure chamber though as I seem to be drifting into clear and specialty casting work lately.

You *can* cast off of a master made from foam- Oomoo is a low-temp curing silicone which should work for it- not sure what others have/would use.

 

[Psygnosis]

thank you for your advice.

can I ask you what is the use of the body filler on props? is used just for fill gap? or as layer to give a smooth surface to all the prop?
Bondo is not sold in italy, can I use any body filler for car?

So I can make a mould of pretty anything foam, wood, polystirene (prepped) right?

 

[Zlurpo]

Bondo is just a brand name, any body filler paste will work. It fills gaps, and it can be sanded very very smooth.

Most things can be molded, but anything with porous surface will hold onto the silicone, and may cause it to tear. You should have a good sealing layer or paint or mold release on them.

Never use clay with sulphur in it, as it prevents the silicone from curing.

There are dozens or perhaps hundreds of types of resin. Epoxy is one of the types, and it does some things very well and some things poorly.

To know the approximate volume of a casting, fill your mold with something like rice or popcorn, and then pour it into a container. That's about the volume or resin you'll use, and rice and popcorn shouldn't leave almost any residue inside your mold.

 

[falloutboy]

Also- before you apply body filler, cover the surface with a acrylic brushed on paint. This gives a protective barrier- It should prevent most reactions to the foam, and you can spray paint then if wanted.