Great stuff shrinkage

Blackrose1978 · #1 04-21-2012

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/

Bone Dancer · #2 04-21-2012

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.

Blackrose1978 · #3 04-21-2012

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.

zombietoxin · #4 04-21-2012

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.

scareme · #5 04-21-2012

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.

partsman · #6 04-21-2012

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.

Demon Dog · #7 04-21-2012

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.

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.

debbie5 · #8 04-22-2012

"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....

Blackrose1978 · #9 04-23-2012

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

Bone Dancer · #10 04-23-2012

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 .