[TheOneAndOnlyKelly]

Earlier this month I created a paper mache skull by wrapping paper around a Bucky skull then removing said skull after about 3 layers. After taping it back together (tapier-mâché, if you will ), I proceeded to pump it full of Great Stuff™ expanding foam insulation and let cure.

Last week I revisited my new creation to add teeth to it and lo, parts of the cranium were collapsing inwards. It would appear that the foam started to shrink, pulling in the walls of the skull with it.

Has anyone experienced this before?

(I've resolved to add plastic wrap inside the skull before trying this to avoid having to perform trephanation on my work...

 

[tot13]

Yep. It was equally surprising and disappointing. I'm not positive, but I don't think the foam shrinks. I think it's air pockets (and I know that may sound stupid) that get trapped under a heavy layer of fresh foam. I've only managed a few times to achieve a solid head or skull using foam. If the empty area seems too large, I just poke a hole through the mache and squirt in a little more foam. But I've also found that it's best to wait a few days before doing this.

I seem to get better results if I only try to fill about 1/3 of the skull/head at a time. Give it a few days and come back for the next layer.

 

[TheOneAndOnlyKelly]

What I ended up doing was slitting the caved in area and inserting wadded up toilet paper to pop them out. The paper is flexible enough to go where I needed to.

Here is the skull (Phillip) resting after surgery:

http://halloween.tittivillus.com/Year.aspx?year=2010#PhilSkull3

 

[billman]

Yep, had the same problem. After a couple of days it shrank significantly!