I have a 30 year old fiberglass tub with no support under it - 1.5 inch gap over subfloor. I saw the same question on mar 17, 2009 so wanted to try the recommendations of shoving balls of structo-lite in material squares under the tub and letting it set up. The man at my local lumberyard talked me out of structo-lite and suggested mixing gypsum floor leveler and using it. He said sl is made to be used in thin layers and he was afraid over time, that balls of it would crack and crumble and I'd lose the support. 21boat and massplumber2008 both suggested sl. What does anyone think? How long have you been setting tubs in sl? Will the floor leveler work just as well? This is rental property, the tub is on the 2nd floor and I really don't want to rip it out. It just started creaking in the last 2 months and has some minor stress cracks. Thanks. cward56

Stucco-Lite, Mortar, Thin-Set or Light Weight Concrete are the mixture you want to use for tub support.

Hi all:

I've used structolite in very thick beds under whirlpools and shower stalls and have never had an issue with it cracking or becoming loose over time.

And, just to be clear, I've been using this stuff almost 30 years so as much as I am sure the guy at the local lumberyard meant well... he is wrong!

Stick with the structolite... stuff dries overnight!

MARK