Expanding Foam question.
- Thread starter Tallman50
- Start date
If you create a large (deep/thick) application, the center will lose it's oxygen source and stay uncured although the outer areas (being closer to the open air) will harden regularly. Same thing can happen if you spray an enclosed space with too much foam all at once. My only solution was to spray the foam in layer by layer, letting each application expand and cure before proceeding. I know how much it sucks breaking into the 'melted-marshmallow' goo in the center of an uncured piece.... 
Z0M8I3
Active Member
A problem I had last year when working with expanding foam was even after a 48 hour cure it would shrink on the edges where I carved it. Not sure if it was just the brands I was using but it happened with two different brands. Either way, I would recommend waiting a full 24 - 48 hours before messing with it at all.
Good luck with your project
Good luck with your project
Sand_Storm
New Member
I had that happen on a large chunk of foam I sprayed in all at once. The outsides skinned up nicely but the inside was still runny a few days later. Layers are the way to go.
Knowone251
Well-Known Member
If you have a Hobby Lobby near you, they carry Alumlite products, including Fast Foam 320. Its a two part expanding foam with a 20x expansion rate. Much easier to work with than the stuff in the can. Plus if you get their smartphone app they always have a %40 off one item coupon, making the foam $20ish dollars out the door.
Z0M8I3
Active Member
Thanks for the tip! There's not one near me but sometimes I get lucky to visit the one 3 hours away. Very much appreciated
Had the same problem with a mountain for my model trains. The mountain kept growing after I had contoured it and added the scenery. Could take months for a large blob to cure as moisture works its way in. AFAIK, Great Stuff cures from the moisture in the air (not sure about the oxygen...). Solutions: layers, spritz with water now and then as you spray more foam and add to the glob, 'air (moisture) tunnels,' stick in a knife and see if it comes out clean (the 'bake-a-cake' method). As far as poking holes breaking the cell structure, it should only affect the areas around the hole. If you space the holes no closer than 1" apart there should still be enough integrity to hold the blob together.
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--Paul E Musselman
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--Paul E Musselman
clonesix
Master Member
Good info people. I did not know this. My first thought was improper mixing.
Question to original poster: were you pouring the foam for the purpose of carving it into another shape? I ask because I too carve urethane foam into my props, but I start with solid block, as opposed to pouring the liquid and letting it expand. The reason is that a solid block has very uniform consistency, where a poured mass is rarely mixed as thoroughly and as a result has a non-uniform consistency. I like carving and sanding something that is has a tight bubble structure, doesn't flex, and any tool that is applied to one part, is exacly the same consistency as the next.
I also have the luxury of being close to a manufacturer of large foam buns that get cut down for insulating pipes. So they can make a 3'x4'x3' block, and cut it to any size. If there is no source close to you, there are web-based taxidermy suppliers that can ship you blocks.
Question to original poster: were you pouring the foam for the purpose of carving it into another shape? I ask because I too carve urethane foam into my props, but I start with solid block, as opposed to pouring the liquid and letting it expand. The reason is that a solid block has very uniform consistency, where a poured mass is rarely mixed as thoroughly and as a result has a non-uniform consistency. I like carving and sanding something that is has a tight bubble structure, doesn't flex, and any tool that is applied to one part, is exacly the same consistency as the next.
I also have the luxury of being close to a manufacturer of large foam buns that get cut down for insulating pipes. So they can make a 3'x4'x3' block, and cut it to any size. If there is no source close to you, there are web-based taxidermy suppliers that can ship you blocks.
