bathtub
I'm installing an enamel on steel bathtub on a concrete slab. Any good ideas for what can I do to make it feel and sound less flimsy and hollow?
Edit: How about lead diving weights as harmonic dampers, attached to underside of tub with structural adhesive, surrounded/supported by Great Stuff foam, on top of a bed of scrap pressure-treated 2×4–I imagine that's a bad idea for some reason(s), but I propose it as a serious question. Why not?
If you look at the underside of the tub (through your proposed hole) you should be able to tell if it was meant to sit on the subfloor or not. Some kind of wooden frame will be partly embedded into the fiberglass to help support it. If there are "skids" that should touch the subfloor but do not you can use shims to support them.
I had a shower enclosure that was not well supported underneath. It eventually cracked and leaked on the ceiling below. When I removed it, it was obvious that the enclosure was sitting on the floor in the front and hanging from the wall in the back. The reinforcements on the bottom of the enclosure were not touching the floor. I don't know if they were meant to or not.
You can buy bathtub splash guards such as the ones found here.
You should be able to find similar ones at your local hardware store. Most versions install in seconds, using easy peel and stick adhesive backings. No tools, no mess, and usually no waiting for caulks and/or glues to dry.
Best Answer
Bed it in plaster (which is very likely what the tub manufacturer recommends - most do.) Foam can work but is not preferred (easier when you have an already installed tub, though.)
Bedding on plaster is literally get ready to go, test fit, dump a pile of plaster on the floor under the middle of where the tub goes, set the tub. Tub ends up solid, you don't have anything that's going to rot in there, and the plaster is easily broken out when the tub eventually needs to be replaced.
As for your cockamaimie scheme, the diving weights alone will cost more than the bag of plaster; and it's an ugly mess and waste of effort .vs. doing it right with plaster.