Indoor sinkhole under by basement tile floor?

July 21, 2018 3:53 PM

My basement bathroom floor has 12” square slate tiles, and for a few in front of the shower stall, I get a disturbingly hollow sound when I tap on them. This bath was put in about 10 years ago, and the area in question is where the plumber dug a hole in the cement foundation to make a new connection to the sewer line. I believe the tile is laid directly on the cement foundation floor.

My best guess is that the shower pan is leaking and eroded the soil under the cement put over the hole. In the meantime, I’ve put down a 24” square tile over the area to distribute any weight placed on it. Anyone ever dealt with something like this? Is the first call to a plumber, or insurance? How does something like this get repaired? My Google-fu hasn’t come up with similar situations. Thanks!

posted by sapere aude to Home & Garden (1 answer total)

Best answer: I don't think it is as serious as that. I would guess instead that your slate tiles have become disconnected from the concrete that is under them, and now sound hollow when you tap them. If I had to guess, sight unseen, I would guess that the shower door or the shower threshhold leaks, and the tiles have gotten a lot of water under them over the years.

I have some slate tiles on concrete that sound hollow when I tap them, but I'm certain it's not because the soil under the concrete has eroded away. In my situation, water has eroded or compromised the mortar underneath the tile, and the tile is no longer tightly connected to the concrete. I could gently pry the tile up, if I wanted to, but then I'd have to fix it, so I haven't.

You probably have a leaking shower, like you guessed, but I wouldn't expect a sinkhole. I would see if you can gently pry the hollow sounding tiles up, to see what's going on underneath. If it doesn't come up very easily, don't force it.

I don't know that I'd call anyone to fix it, if there were no symptoms other than sounding hollow.
posted by the Real Dan at 4:46 PM on July 21, 2018