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 2x2 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.


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.

  • How is plain dirt insect and corrosion resistant? I was told that it's left as dirt to access the trap.
    – Chris
    Mar 13 at 22:47
  • A layer of polyacrylic would be rodent and insect proof. Can you clarify your answer?
    – Chris
    Mar 13 at 22:48
  • 1
    Dirt is not insect and rodent resistant. Thus, your "installers" leaving it like that constitutes a code violation, as I understand it. How is that not clear? The "polyacrylic" I'm familiar with is a finish, and finishing dirt is not on the can label - even if it was, I would bet on the mice & rats winning 10 times out of 10. Chewing plastic is nothing to a rodent. To "access the trap", having removed the tub, you remove the new concrete you poured in for an insect and rodentproof barrier after installing the trap. Use a 2" trap as required under concrete, making "access" less needful.
    – Ecnerwal
    Mar 13 at 23:33
  • Or you could make it so the drain pipes sit above the slab -- I know, sacrilege, right?! Mar 14 at 3:43
  • 1
    If you want to form and pour sides and a bottom for the pit, sure. Thing is, it doesn't really save a lot of work - a tub trap is not somthing that should need "servicing." I made sure mine was all set and happily poured enough concrete that only the trap connector is poking above the surface of the pit. In the unlikely event I need to get at it, half an hour with a sledgehammer and chisel should have me in there, since the pit bottom is not full slab thickness (or it would not be a pit, and the tub drain would not fit.)
    – Ecnerwal
    Mar 14 at 14:23

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