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Old 04-14-2011, 01:24 PM
joshatlas joshatlas is offline
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Join Date: Mar 2011
Location: Los Angeles, CA
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Question Help with Spray Polyurethane Foam

Hi everyone,
I'm a sculptor that recently used some great stuff as an armature for
sculptures. Inside these buckets, I used great stuff foam to build up shapes to cover with icing.

The problem is, the great stuff will shrink dramatically. As it shrinks, it pulls at the icing, causing the icing to crack/flake off.

Here are my questions:

1. Are there any spray polyurethane foams that will not shrink after curing? If so, do you have any brands that you recommend? (Please note, I am looking to buy relatively small quantities if possible).

2. Since I already have several sculptures made with the great stuff, is there any sort of sealant or surface coating that I can apply directly on the foam in order to prevent future cracking?

Thank you in advance for your help.
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  #2  
Old 04-14-2011, 08:16 PM
raspero raspero is offline
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Join Date: Oct 2008
Location: Huatulco, Mexico
Posts: 544
Re: Help with Spray Polyurethane Foam

I have used polyurethane foam for years, but always in the two part liquid form, not the spray. I can't find any situation that a spray would be necessary, and from what you describe, the quality of the spray is lower. The two part liquid does not shrink or crack. As far as I can tell, if kept out of the direct sunlight, it will last approxamately forever. It costs me about $30.00 for two one pint cans, which will expand into about seven gallons of foam if mixed and poured at around 80 degrees.

Richard
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Old 04-14-2011, 08:34 PM
joshatlas joshatlas is offline
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Location: Los Angeles, CA
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Re: Help with Spray Polyurethane Foam

Thanks for the advice, but I've had a little bit of trouble with the two part systems. It starts to expand so fast that I found it difficult to control where the foam landed. I have seen some two part foam kits that come with spray guns, but wasn't sure if particular brands would shrink or not....
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  #4  
Old 04-15-2011, 06:49 PM
raspero raspero is offline
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Join Date: Oct 2008
Location: Huatulco, Mexico
Posts: 544
Re: Help with Spray Polyurethane Foam

It doesn't give you a lot of time does it? You must plan your pouring process carefully. I have never had it shrink or crack. I have to assume that the quality of that spray can stuff is probably low. After all, it's made to spray in cracks in the walls of houses to keep out cold air.

One way to manage the final shape is to trim the hardened foam to shape with a razor blade knife and then mix up tiny batches of the foam and brush it on. To mix them I use syringes from the baby dept. of the drug store. Red bulb for part A, and yellow bulb for part B. I write on the can which color is for which. The resulting surface can be manipulated into something quite interesting, or it can be sanded smooth.

Richard
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