Molding over Polystyrene (Pink insulation foam)?

jclinton

Active Member
I am looking to make molds from foam items I have carved out. I am using the pink insulation foam form HomeDepot (Polystyrene I think it is called). Can I cover this to make a mold or will it destroy the foam? I wasn't sure if I needed to protect the foam with something or not. Also, are there any recommendations on what to use? I am trying to learn how to mold and cast things that I make.

Thanks for any assistance!
 

hdtheater

Sr Member
RPF PREMIUM MEMBER
I know nothing of molding material, but anything with acetone will eat it alive.

-Eric
 

clonesix

Sr Member
What material do you want to make the mold from?

With the exception of polyester fiberglass resin, you can make the mold without problem. You can use gypsum, or Silicone RTV without issue.

I could give a better answer if I had more details, such as: What is it you are trying to make? What is the final product to be? Are there undercuts or details? Is this a one part, or two-part mold?
 

jclinton

Active Member
What material do you want to make the mold from?

With the exception of polyester fiberglass resin, you can make the mold without problem. You can use gypsum, or Silicone RTV without issue.

I could give a better answer if I had more details, such as: What is it you are trying to make? What is the final product to be? Are there undercuts or details? Is this a one part, or two-part mold?
Okay Thanks for the feedback! My first mold will be vents and another will be like a gas cap looking thing that will be going on a 1:1 batpod. The pieces aren't extremely detailed, but needs to be strong. I made the vents and some of the other part from Pink Insulation foam (Polystyrene). I am not sure what to use for the casting yet. I have some Easyflo 125 I was thinking about trying once I figured out the mold process.
 

clonesix

Sr Member
Pictures speak 1000 words.

Without a picture, I will guess that you are doing a single sided mold? Rule of thumb: If you are making a hard part (ie: resin, stone or fiberglass)you need a soft mold (rubber, Silicone is best) Soft part (foam or rubber); hard mold (fiberglass or stone)

My first thought is tha silicone RTV should work fine for you. It will not damage the pink foam at all. Good luck.
 

jclinton

Active Member
Pictures speak 1000 words.

Without a picture, I will guess that you are doing a single sided mold? Rule of thumb: If you are making a hard part (ie: resin, stone or fiberglass)you need a soft mold (rubber, Silicone is best) Soft part (foam or rubber); hard mold (fiberglass or stone)

My first thought is tha silicone RTV should work fine for you. It will not damage the pink foam at all. Good luck.
Thanks! That definitely helps. I've never casted/molded anything so this will be a new venture.
 

Propsjonnyb

Well-Known Member
To be on the safe side give it a couple of coats of white PVA first, and let it dry , before you continue , it would be a shame if it melted the second you started to pour. If in doubt about the foam type always seal it with a coat of Glue
 

Don Z

New Member
if you did want to make a fibreglass mould, a neat trick is to paint a crazy thin layer of silicone onto your foam. This thin layer is enough to protect against the styrene in the polyester resin
 
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