hmmm thats odd

[NavyNate06]

so my tanks been set up for about a week and it looks great, but i've noticed the GS background is shrinking. i thought that stuff expands and then sets up and stays that way. i might be wrong, has anyone else had this problem? its shrunk almost an inch on both sides. also does anyone have any easy and unharmful fixes to fill the spaces? i'll have pics later.

[froggsong]

In MY experience, if you carve it it shrinks, if you don't it stays the same. Alot of the stuff that I carved for my frog/toad tank experiment shrank in the areas where I carved it, but not in the areas that I did not. The part that is smooth when after curing doesn't shrink, is what I mean. I think maybe when you carve it, since it opens the bubbles created by the expansion, the air pockets inside sort of collapse and it makes it shrink. I could be totally wrong though. Even the stuff that I heavily coated with silicone immediately after carving shrank like that. I actually like how it looks though, the places it shrank most were on the landings, and it made them look more natural.

[alex1976]

I know the can says it will cure in eight hours but you really should wait a full day or more before carving or trimming it. I've used this stuff a lot for casting in latex molds. While the outside may be fully cured and hard in just eight hours, the inside is still "wet" like a marshmallow and prone to collapse. This is what causes it to shrink.
I prepare each mold with a non-stick surface to keep it from adhering to my molds and theirs almost always some shrinkage if I take it out too soon.
My guess would be it didn't stick well enough to your glass and collapsed some inside (from moving/carving/messing with it) before fully curing on the inside.
Did you apply silicone to the glass before spraying the GS to help in adhesion?
Hope that helps!

[NavyNate06]

heres a little view of what it looks like





the corners were flush up against the glass in the beginning. i guess i didn't let it cure enough before working with it. it only sat for about 4 hours. i'm prone to get-there-itis. i have the patience of a 7 year old in the toy isle. if it gets any worse i'll give it a third try on this tank, haha beginners luck.

[smaug]

Yup,you worked it too soon.a full day is needed to avoid that.

[NavyNate06]

so the next question is how can i fill those holes quickly and easily without harming my little guys.

[JohnEDove]

Originally Posted by alex1976

I prepare each mold with a non-stick surface to keep it from adhering to my molds and theirs almost always some shrinkage if I take it out too soon.

What do you use to create the non-stick surface? I am wanting to create some backgrounds for my occupied 10 gal aquariums outside the aquariums then put them in.

[Pufferfan]

mine shrank about a quarter inch even after being coated in silicone. I had to go back and fill in the holes and re silicone.

Originally Posted by JohnEDove

What do you use to create the non-stick surface? I am wanting to create some backgrounds for my occupied 10 gal aquariums outside the aquariums then put them in.

I wraped my filter in suran wrap and then coated it in Crisco. it worked.

[Rainfrog]

I too would like to know what you can use that GS wont stick to.

[froggsong]

If you read Alex's 10 gallon build thread, he talks about using vaseline. He says he makes alot of stuff with GS in molds, so I would bet he would be the authority on it.