Sealing Polystyrene foam?

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Crank729

Sr Member
I need to know of an easy way to seal polystyrene, or insulation foam. I know urethane resin works, but I don't have any on hand. Any easier ways? I have heard that acrylic paint can seal it, but I just wanna double check. The foam needs to be sealed so it can withstand a coat of bondo.

Thanks guys.
 
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Palendrome

New Member
I've used acrylic lacquer to seal foam--but I haven't had issues with bondo degrading the foam in the past. If your foam has a rather porous exterior than it may take several coats to seal everything. If you use foam in a mold and allowed it to self-skin then you may be able to get away with one or two coats.
 

Wellss01

Member
A really great thing to use is Gesso, you can pick it up from any art store and it works GREAT for sealing foam.
 

MattMunson

Master Member
RPF PREMIUM MEMBER
Gesso is THE way to go. Not only is it cheap and easy to get, but it is perfect for the application you are describing. If you put bondo straight on pink foam, it will dissolve it.
 

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Kailon

New Member
I learned pink foam and bondo don't mix the hard way...great way to make yourself have to remake a large peice...oh well, gave me a chance to fix parts I thought was wrong...now that i think of it, its the same way I learned fiberglass resin hardener doesn't mix with foam brushed, but it has a really cool chemical reaction though lol.
 

tk5378

Well-Known Member
You can also wrap the foam in aluminum foil and then use bondo. Never tried it myself, but I've seen it done with pretty good success on a large scale project.
 

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Dogless

New Member
Many moons ago while I was in University, I manufactured and sold terrain for use in Wargames rto make a bit of money. I tried many different methods to seal various polystyrene foams, most have been mentioned here. I settled on one of two methods.

1) For pieces that didn't need to have a super hard coat, I would spray a mixture of PVA and Water at around 50:50, tinted with artists acrylic paint.
2) For harder wearing pieces, I added powdered cement to the above, which created a very tough outer shell. This needs to be brush painted, for obvious reasons. Probably not suitable for most prop work as it creates a rough surface texture, but I mention it here as someone may have some use for it.

These days, I don's use much foam, but if I did I'd probably go with Gesso, or if I was in a hurry PVA/Acrylic paint mix through an airbrush.
 

jadebmr

New Member
I carved something out of this stuff and want to be able to paint it to look like a wood texture. What is the right stuff to seal it with? Not sure what kind of foam it actually is other than "floral foam". I would like it to be hard and solid.


Thanks in advance and sorry if I should have started a new topic but it seemed like it make sense to ask here.

foam.JPGcarved.JPG
 
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cavx

Master Member
RPF PREMIUM MEMBER
Epoxy can apparently be applied directly to polystyrene foam (closed cell).
 

Spyhunter2k

Sr Member
RPF PREMIUM MEMBER
Old school guys designing kit car bodies used to seal plaster with latex house paint, and Bondo'ed over that. Could be used in a pinch over foam as well. My go to is epoxy resin.
 

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GaryArm

Member
An Old School way I have used in the past is to brush a sealing layer of wood working “PVA”. This has zero reaction on the Styrofoam, this has worked on many of the job I have done in the past. Polyester Fiberglass can be layed over it with no problem. Although as Spyhunter2k has stated, epoxy resin can be applied directly to Styrofoam, and has no reaction to the foam.

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An Old School way I have used in the past is to brush a sealing layer of wood working “PVA”. This has zero reaction on the Styrofoam, this has worked on many of the job I have done in the past. Polyester Fiberglass can be layed over it with no problem. Although as Spyhunter2k has stated, epoxy resin can be applied directly to Styrofoam, and has no reaction to the foam.
 

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