Great Stuff under tub?

I'm thinking of putting Great Stuff under my fiberglass tub to help get full support between it and the subfloor when I install the tub.

Should I be using the Great stuff for Windows and doors? (Expands to fill spaces, but doesn't have enough force to bow vinyl windowframes) I guess I'm wondering if I should be worried about the regular stuff expanding too much and pushing the tub up.

Nate R said:

I guess I'm wondering if I should be worried about the regular stuff expanding too much and pushing the tub up.

Click to expand...

As well you should be.

On the other hand, the minimal-expanding cures pretty soft - too soft to count as "support" of any kind.

If you go with the great stuff, use as little as possible - maybe do some experiments out in the garage, first, to get a feel for it - and fill the tub so that the weight will keep the tub from rising.

Or, of course, you could do it the normal way, with mortar.

Try StructoLite. It's a type of perlited gypsum plaster that doesn't shrink, is easier to work with than mortar, it doesn't scratch surfaces and is easy to clean up.