Sudden wet spots on grout lines

[dvnwvt]

2-1/2 year old ceramic floor. Professionally laid with Schluter Ditra on plywood subfloor. Grouted and sealed.

Has been fine all this time but out of nowhere, 3 or 4 separate wet spots on grout lines have appeared, in the same area. They are 3-6” long each, and separated from each other by a few inches.

It’s been humid here but nothing at all out of the ordinary … certainly no worse than other years. The ceiling beneath this area is finished and no water stains (yet). Any nearby water lines run in the joists below. I’m totally stumped how moisture could find it’s way between tile and subfloor in the middle of a room. No spills either.

When I dry them with a heat gun, there is some whiteness (it’s a somewhat light grey color grout).

Here’s my suspicion … we clean with an oxy-clean solution and possibly these areas weren’t rinsed thoroughly, and perhaps are now retaining moisture from the air? That’s all I got.

Any other thoughts?

[cx]

Welcome, Dave.

A photo of what you're looking at might be helpful. Perhaps spark someone's imagination, or bring back an old memory.

I'll just state the obvious: If it's actually a wetness issue, the moisture has to be coming from somewhere. Helpful, non? I'm assuming this is in conditioned space and the space below is also conditioned? No pets or children hang out in this room? Spills or leaks elsewhere that might have migrated consistently through the Ditra? Is this a low spot in the room?

Can't guess what oxy-clean product you might be using.

[dvnwvt]

Here are some pics. After scrubbing with some water and letting them dry, they may be getting shorter, so my oxi-clean theory might be the thing.

[John Pride]

I'm with CX on the low spot question. That's what water seeks, after all. If that's part of the issue, do you have access to look beneath the area, to see whether the sheathing is damp or water-stained? I know you're waterproofed, but it's worth a look, if possible. If it's near the kitchen sink or bath lav, maybe it's related to that? Bottom line: It's potentially water where it shouldn't be, so a slow leak from a dishwasher or sink could be causing problems that'll cost you later. If you can eliminate that concern, maybe it's an oil or other stain that's "cleaned" and gone, but wicks back to the surface over time. If so, I'd dig the grout out and re-grout it, being careful not to cut the waterproofing.