Basement – Sealing 2-ft square hole in cement beneath tub

basementbathtubcement

We are having our bathroom in the basement redone. Having a tub installed and the installer cut a 2 ft wide hole in the floor beneath the tub. after the tub is installed I was told that they no longer fill in the 2×2 ft hole.

However the dirt shows moisture. Seems unclean and unwise.

What can I pour into the hole to seal it?

A gallon can of water based exterior polyacrylic?

I asked if I can pour in liquidity cement and they said that is no longer done.

Best Answer

Well, that's a code violation, at least under IPC.

1002.8 A recess provided for connection of the underground trap, such as one serving a bathtub in slab-type construction, shall have sides and a bottom of corrosion-resistant, insect- and verminproof construction.

Additionally, it sounds like the tub (with a 2 foot square hole under it) may not be "bedded" - which is OK if it's cast iron, and otherwise dubious - plastic and thin steel tubs should have material filling between the tub and the floor (plaster is traditional, some folks use sprayfoam these days) to prevent it from flexing (and eventually cracking) when loaded with water and a person's weight.

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