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Unread 04-30-2013, 04:41 PM   #1
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Insulation foam and resin...again!

I know it's likely been asked many a time, and I've looked through the forums for the various solutions, but I must ask...

What is used to protect insulation(blue/pink) foam from both the heat and chemical reactions associated with resins? Specifically urethane, or fiber glass, resin. We've tried a number of coatings, gesso, Durham's putty, and plaster of paris amongst them. They all provide some protection, but there is always some damage to the foam.

I appreciate the help, in advance.
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Unread 04-30-2013, 05:14 PM   #2
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I've heard white masking tape works.
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Unread 04-30-2013, 05:18 PM   #3
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Have you seen, or used it, yourself? I'm willing to bet it would stop the resin and the foam from coming into direct contact, stopping any chemical reaction from eating the foam. However I suspect the heat would still be an issue.
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Unread 05-04-2013, 11:39 PM   #4
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What urethane resins have you used? Smooth-On's Shell Shock, for example, can be applied directly to foam, with no barrier, and no distortions at all.

Regarding fiberglass resin (more accurately, polyester resin), you might be mixing a little too much catalyst. The more catalyst you mix, the faster it will kick off, and the hotter it will get.

Personally, I've moved to using PU and epoxy resins, so I haven't tried polyester resin over foam, but from what i hear, a couple coats of gesso should be enough to prevent heat distortions on most all but the really pointy bits.

Usually, if it does distort, it just makes some air pockets. For props, this is often not a problem, it just makes thing a bit less sturdy. If this is important, you can drill a pinhole into the distorted area, and inject a touch of gorilla glue. It foams a little as it cures, so this should fill the void.
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Unread 05-06-2013, 09:43 AM   #5
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Here are my findings on foam + polyester resin (the cheap caustic stuff you get from Home Depot/Lowe's). It does eat it hard, but I've used either a bondo layer, or oddly enough, a thorough layer of masking tape. Just make sure with masking tape to do 2 layers to cover the seams between tape pieces.

You can see failures of foam + resin as well as triumphs here:

Foam protected with bondo

Foam protected with plaster tape

Foam protected with masking tape


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