Just bought a new house - new to me, but it's from '52. My bathtub looks like it's relatively new, and at first use was great. When we recently used it for a bath, however, it felt like there was some water... underneath the floor of the tub? It could be moved around, like a water bubble underneath a lawn.

Worried, I checked the basement - but there's no leak, nothing's even wet. What in the world is going on, and how do I fix it?

Even when the bathtub is empty, the water underneath the floor seems to remain - and it's got worse again when we tried taking another bath (which, in both pro-and-retrospect, we probably shouldn't have done).

enter image description here

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    What is the tub made out of? Is there a liner or refinished surface in the tub? How does it feel like there's water underneath the bottom of the tub? Is the ceiling in the basement beneath the tub finished? Try filling it with cold water and seeing if the same thing happens. The bottom might be getting heated up by the hot bath water, expanding, and getting bent up out of shape. Then it acts like what you describe: press down one side, the other side pops up. Apr 25, 2023 at 17:59
  • It's literally actually filled with water underneath, I'm pretty sure: I can feel and hear it sloshing when the tub is empty and we press on the spots (which remain). I don't know what the tub is made of but I'm guessing fiberglass, seems relatively new. The ceiling isn't finished, but I don't have good access to the underside of the tub.
    – user112697
    Apr 25, 2023 at 18:05
  • @aquaticapetheory Should have "@"d you, but neglected to do so. Don't know if an edit will trigger it, so I'm just commenting again.
    – user112697
    Apr 25, 2023 at 18:05
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    Does the side of the tub have a panel that can be removed? What is the basement ceiling beneath this made of? Are you able/willing to cut it open? Can you make a video, with sound, of this sloshing effect and post a link to it here?
    – jay613
    Apr 25, 2023 at 18:28
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    @jay613 I've got the video, might be a bit quiet. My phone sorta sucks. youtube.com/shorts/qQgxmQYHARg Also: I THINK the stack is in the wall by the sink, not by the tub unfortunately.
    – user112697
    Apr 25, 2023 at 19:10

1 Answer 1


You probably have a bathtub liner with a hairline crack, and water between the liner and original tub.

If a renovation of this bathroom is on the horizon, you may opt for a short-term fix to temporarily get rid of the water. Since you have access from the basement you can remove the drain basket, then most of the water in the liner will flow into the drain. Some water may end up on the basement floor. Also look for the cracks or wherever the water is getting under the liner and seal that. Don't re-use the basket or the drain shoe washer. Watch youtube videos on how to replace a bathtub drain and use new parts as much as possible.

If a renovation is not on the horizon you may be able to replace the liner or remove it and reglaze the tub.

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    @user112697 If you do a freestanding tub with a shower curtain, you don't have to tile the walls or worry about the wall and ceiling to tub joints. Sounds like you already have enough to do... Apr 25, 2023 at 19:43
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    In my experience the money to replace a bathtub which is usually in an ageing bathroom is better put in a piggy bank towards a total renovation of the room.
    – jay613
    Apr 26, 2023 at 15:10

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