I moved into a new house a few months ago, and had a leak from my (freestanding) tub. After taking out the drywall in the ceiling in the room below, I realized I had to lift the tub up to get to the drainage pipe. After doing so and turning it on its side, I saw all of this...stuff that was under the tub. It almost looks like some sort of foam that I assume was meant to be some sort of "cushion" when the tub was installed, but in looking at all of the tub installation instructions I can find, I don't find any mention of putting stuff like this (or any kind of cushioning) under the tub.

Also it's much denser than foam (but that could be caused by the leak completely soaking it). What is this, and when I reinstall the tub, do I have to do something like this again? Here's a photo:

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1 Answer 1


Your tub space is odd looking, It appears that your tub had an oval bottom.

For standard tubs The tubs are set in a base of foam or sometimes a cement type product to provide a solid bed for the bottom of the tub to rest on.

This is done to support the bottom of the tub and keep it from flexing.

If it was not there the bottom of the tub would be free floating and the flexing could, over time, cause issues at the mounting points on the rim of the tub thereby causing loose and or noisy connections.

  • 1
    Thanks, that makes sense, but again, I can't find any mention anywhere of this foam base - is it necessary for a freestanding tub or just a standard tub? And yes, the base is oval (as is the overall tub, but it tapers down to the base).
    – Jer
    Commented May 1, 2020 at 17:52
  • Not only flexing but de laminated for some types of tubs and cracks in others. The bedding supports the bottom and is critical in almost all modern tubs.
    – Ed Beal
    Commented May 1, 2020 at 18:21
  • Yes - the use of this form is very common now under bathtubs. Commented May 1, 2020 at 18:30
  • I don't doubt you (especially since now multiple people are saying the same thing and the original installer did this) but is there a reason why the installation manuals for the tubs don't make any mention of doing anything like this?
    – Jer
    Commented May 1, 2020 at 18:40
  • 1
    Because those that install tubs pick up tricks from the people that taught them, plus they don't read the manuals.
    – Gunner
    Commented May 1, 2020 at 21:25

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