1. If that is true, then there are a LOT of people who are going to have to replace the foam insulation around their windows and doors, and also around outer wall electrical boxes.
- 1. First, the foam breaks down over time (and by over time I mean almost immediately)
- 2. Second, the cured foam is exactly the consistency of a sponge. Any condensation or outside moisture that invades the space under the tub will be soaked up and turn into black mold very quickly
- 3. Third, the foam is soft and does not properly support the weight of water, much less the weight of one or two people
- 4. Finally, the foam expands dramatically while curing, causing the same issue you had with it lifting the tub away from the tub deck
2. IF the foam were the consistency of a sponge, which it is not, it would still be a "closed cell" material which does NOT absorb moisture.
3. If it is soft, also not a fact, then it would not support the tub or the people in it, but then,
4. Neither would it be strong enough to "raise" the tub, regardless of how much it expanded.
5. You should use low expansion foam anyway, since it is the densest.
If it means anything my whirlpool tub is supported exactly the same way (wedges and expanding foam). I suspect that its probably not the best way to do it, however the tub is still level after 5 years. I don't remember if he filled it with water or not while waiting for it to cure although I can see why one might want do that.