I've got a similar question to a thread below. I have a crack in some grout that I'd like to fix. Can I just find a match and repair? Or might I have some underlying problem that I need to fix first? Here's a shot of the crack as well as a cross section from my basement stairs. The part of the house with the tile is on a slab (tri level house) but I can't tell if there is underpayment between tile and slab. Could settling of the slab cause this?
I bet if you stand on those tiles with the cracked grout and move your feet up and down, you will notice very slight movement of the tile. Underlying problem is bad foundation. Unless I am missing something in your photos, I do not see any underlayment board. Here was my install: been 18 months on a 450 sq ft install and not a crack anywhere. You can't see much of the subfloor in my photo. Also supporting the floor are 2 x 10 joists spaced 16" O.C.
Last edited by hammerlane; 09-22-2012 at 08:09 AM.
If it's on a slab he doesn't need a cement board underlayement. I don't see any crack isolation membrane like Ditra either. It's just tile set right on the concrete. If there is any movement in the slab it transfers through to the time. Since it's cracking the joints and not the tile itself I'm apt to believe those tiles may not be firmly mortared into place. If they were solid, cracks in the slab would telegraph right through the tile, not the grout joint.