Silicone shrinkage issues?

[Hez]

Hoping someone can help with this, I used some por-a-mold thixatropic from Dick Blick to mold a helmet, and had a couple of issues with it. Firstly, it took ages to cure in a couple of spots on the inside of the mold, it was tacky for a while. Secondly, now that I've started pulling casts from it, they have what I would estimate to be around a 4% shrinkage on them.

Is this normal for this silicone, or did I get a bad batch? As it is I'm considering just tossing the mold and starting again with something else anyway, any recommendations?

 

[exoray]

I'm almost certain that that is a polyurethane rubber not silicone...

So yes shrinkage like that is probably happening, you won't be able to measure the shrinkage with silicone in most cases...

Confirmed that Sil-Mold line is their silicone rubber, the Por-A-Mold line is polyurethane...

 

[Hez]

Dangit...it was listed along with the silicones on Blicks site. I guess that's what I get for assuming. Mind, I just checked and Blicks never states that it isn't a silicone either. :unsure

 

[ArtisanProps]

Yes, and if you want the least amount of shrinkage (insert joke )
Go with a Platnium Cured Silicone, the shrinkage is negligible unless otherwise
stated in the tech bulletin..........

 

[Tim Allen]

Ive been using this silicone from smooth on called Rebound 25, really easy to work with A+B and added a thixotropic to it didnt have any weird effects with the curing or shrinkage. If their was any shrinkage I sure couldnt tell to the human eye