Not sure if this is mildew or what - black marks on tile

Old 01-21-21, 10:48 AM
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Not sure if this is mildew or what - black marks on tile

Hey all so these black circles have appeared in my master shower, along with scratches. Very odd. Not sure if this is possibly water behind the tile seeping thru. Before I get too far along just trying to get an idea from folks that know more than me. Any help is appreciate on what this is and how to best treat it. Thanks

Old 04-27-21, 11:43 AM
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Looks like you have similar spots to me. Are they all on the lower row of tiles? In your case, it looks like the tile has a crazing pattern of hairliine cracks that has allowed moisture to penetrate into the ceramic. One of my spots has this pattern as well but most do not. If you ever figure it out, let me know please.
Old 04-28-21, 01:39 PM
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Interesting. I've never seen mold penetrate a tile like that. Typically it will creep around the grout or the grout will soften from water being behind it and then start to mold.

That looks more like a defective coating or glazing on a tile.
Old 04-28-21, 02:29 PM
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You might be able to detect cracks from the front. Run the point of a needle across the lines and see if it "hangs" in a groove.

If so, then it's defective glazing.

Sorry I don't know what to do if that is the case. Maybe try bleach, and then seal with something?

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