Q. I'm hoping for some help regarding our bathroom floor which is a dark grey very porous tile that is not glazed. There has been a ring of moisture around the base of our toilet on the tile that varies at time in size from 1/4 inch to 2 inches wide. In the past couple weeks it has appeared also around the sink base as well as numerous dark spots appearing all over the floor. So clearly it's getting worse and I know it's not coming from above the tile i.e. Me. We live in a condo on the 5th floor and just had wax ring replaced plumber said it wasn't that. These moisture spots have suddenly started to disappear and I find it suspect that over the past week the water has been shut off in the building almost every day from 9am-1pm. It'll be interesting to see if the again appear over the next few days. But I have a plumber coming in 2 days and I need some information/help as to if it's normal to have all these moisture spots or if it indicates a leak since it's never been like this before. Thank you very much!
A. What you’re describing isn’t normal for a porous, unglazed tile floor and strongly suggests moisture coming from below the tile rather than anything happening on the surface. Porous, dark tile doesn’t suddenly start showing rings and scattered dark spots unless moisture is getting into the substrate. The key detail is that these spots disappear when the building water is shut off, as you mentioned. There could be a pressurized leak in your unit, a neighboring unit, or a shared building plumbing line.
When the water supply is off, it allows time for the tile to dry. When the supply is turned back on, chances are the water will start migrating under the tile again, and the spotting will quickly return. Since the tile is porous, it essentially soaks up any moisture that travels through the thinset or mortar, and the real source of the moisture may not be directly under the spots you see.
Before the plumber arrives, you can check the toilet and sink supply lines and shutoff valves to see if anything feels damp, just in case. You can also press gently on tiles near the affected areas to see if any feel loose or hollow, which can indicate moisture beneath them.
You're right to suspect this isn’t something caused by moisture coming from above the tile, such as humidity, condensation, or routine bathroom use. It’s good you called for help, because moisture under tile can cause long-term damage to the subfloor, contribute to mold growth, and affect neighboring units in a condo building.
Article ID: 826
Created: November 19, 2025
Last Updated: November 19, 2025
Author: Alice Dean
Online URL: https://surfacecarepros.com/kb/article/could-moisture-spots-on-my-bathroom-floor-indicate-a-hidden-leak-826.html