# Great stuff shrinkage



## Blackrose1978 (Aug 13, 2011)

Ok I have been using Great Stuff foam for projects since 2008 but this year the skulls and other things I have used the G.S. on are shrinking badly. I don't mind a little shrinkage but these are just shriveling up. I had one cool skull shrink so bad it will make a nice shrunken head but not what I needed it for. Has anyone else had this problem/


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## Bone Dancer (Oct 7, 2005)

I have tried to make stuff with GS as well. I have found if the item is to thick the inside stays gooy and does not cure. A friend gave me a possible solution that I have not tried yet but it sounds like it will work.
For the skulls I plan to insert a tube or small can in from the neck. It will have to be well greased with mold release (car wax, cooking oil, ect) because it will be taken out just after the outer layer of GS starts to cure. This will make a void on the inside of the skull so air and moisture can get to the GS so it will cure correctly.
Not sure if it will work, but it sounds like its worth a try to me.


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## Blackrose1978 (Aug 13, 2011)

Yeah I had the not curing trouble with my full skulls that I make from a mold the weird thing is I've used this mold for several other skulls in past without this trouble. My half skulls are the ones shrinking the worst and they are just one layer thick. I did notice too that my son's body that I added a little foam to shrank as well. I am begining to wonder if I don't have a bad batch.


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## zombietoxin (Aug 3, 2010)

Great Stuff normally uses the moisture or humidity in the air to cure and harden. If your humidity is low, or more likely, if you are foaming and enclosed space you are probably sealing the outside humidity out and the inside cannot cure fully.

Try misting the inside of the mold or prop with a sprayer before applying the foam, and if its a large area- like a head- fill it in layers- letting each cure before doing the next.

I think the worst shrinkage issues are related to touching or squeezing the foam before its fully cured- bursting the bubbles and collapsing the foam.


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## scareme (Aug 29, 2006)

I've had a lot of shrinkage when I use it inside cheap masks. I used it outside in the hot part of summer, so maybe there wasn't enough moisture. 

Bone Dancer, let us know how that idea works when you try it.


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## partsman (Feb 26, 2008)

I've had shrinkage problems with great Stuff as well, and I was using the misting method to ensure quicker cure time, I've noticed when I use moisture to cure Great Stuff, I get this problem a lot more, or when I use it and there's high humidity in the air I get shrinkage, my thoughts are that when the humidity goes down or the air temp drops, the moisture in the bubbles condenses out of the air in the bubbles creating a vacuum and causing my project to shrink. When the temp goes back up the project expands again. So I try to only use Great Stuff in extremely dry environments. In the Summer this means I create a small workspace in my basement with plastic and place a dehumidifier in there set to 30% or less humidity. These projects never give me problems with shrinkage.


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## Demon Dog (Mar 30, 2009)

I shot a 2 foot by 6 foot area of GreatStuff as part of a Hell scene facade (painted and with inserted Christmas lights for the glowing embers look) to insert into one of our windows. I had made a three sided frame to contain it, and had braced it to keep it's expansion from pushing out the sides. That kept it from expanding, but the shrinkage pulled the sides in many inches, ruining it. :madvil: Attempt #2 had stronger framing plus some wire fencing strung between the framing for the GreatStuff to also cling to (the plan was to use it like the wire mesh in a cement pore). That worked, and nine months later its still holding its shape. If possible, I'd suggest trying some sort of an insert (eg, kids hard plastic softball) in your skull mold that would give the piece more structure and limit the amount of GreatStuff - and its shrinkage. Spritzing lightly with water also helps the GreatStuff cure.


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## debbie5 (Mar 2, 2007)

"I did notice too that my son's body that I added a little foam to shrank as well."

This is probably the only place you can type that sentance and not have the Feds at your door....


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## Blackrose1978 (Aug 13, 2011)

lol Debbie5 I didn't even realize how bad that sounded til I read your post!! peeking out the window just in case they are going to come take me away hehehehe


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## Bone Dancer (Oct 7, 2005)

Having a "bad batch" is possible, but I have noticed that it doesnt keep well from one year to the next and it doesnt take freezing at all. 
I'll make sure to let you know how the experiment goes on the skull .


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## Blackrose1978 (Aug 13, 2011)

I have a few props I made from great stuff that have lasted for several years with just needing paint touch up! Is there a better foam product that is simple to use that I can mass produce skulls with? My plaster paris skulls are just too heavy when it comes to storing.


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## Bone Dancer (Oct 7, 2005)

I think what you maybe looking for is what is called two part foam ( expanding urethane foam )
It can expand at various rates to give you different densities of foam. Here is a link to Smooth On to get you started. Check around for other suppliers and do a search here in the forum.

http://www.smooth-on.com/Rigid-and-Flexible/c10/index.html

Another note, its not cheap.


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## Xeno_god (Oct 5, 2013)

Much like what DemonDog had built, I had a Toxic waste bridge with three 1'x7' panels with lights and Great Stuff Foam. Left outside to fully cure and that night it rained. The next morning, the Great Stuff had shrank 75%. Possibly too much humidity or maybe the nature of the foam in such a wide coverage.


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## dudeamis (Oct 16, 2011)

This guy has some solutions


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