Halting Grout Cracks
Q: "What can we do about grout cracks in our bathroom?"
We just remodeled the upstairs bathroom in our 140-year-old house. The contractor did a fine job, but there's one thing that doesn't seem right: The grout is cracking in the shower where the tiled walls meet, and where the tiled walls meet the tiled floor elsewhere in the bathroom. The contractor has been back a few times to put more grout in the joints, but they still crack. What's going on?
— Richard, Waterford, MI
Joe Ferrante replies: Walls and floors in wood-framed houses are always moving a bit. That's just the natural result of changes in indoor temperature and humidity, along with wind and snow loads on a house. Unless certain precautions are taken, grout can't keep up with the movement and will continue to crack.
I always start wall-tiling jobs by screwing cement backerboard to the framing, taking particular care near joints to make sure that every screw hits a stud. Then I pack the corners with latex-modified thinset mortar and immediately reinforce the joint with self-adhesive nylon mesh joint tape. Finally, I trowel a skim coat of the mortar over the mesh on each side of the corner and wait a day before tiling. That gives me a solid corner and a good base for grout.
Since your tile is already in place, try a different grout — one mixed with a latex-based grout additive instead of water. This makes the grout stronger and more flexible. I prefer it to caulk because it's easier to touch up later, if necessary.
To fix your cracks, have your contractor rake all the grout out of the existing joints — and I mean all of it. Then have him install new grout mixed with flexible grout additive. If the corners were mortared and taped as I just explained, you shouldn't have any more cracking. But if the new grout cracks, then caulk — I use a mildew-resistant silicone — may be your only realistic option, short of ripping out the corners and doing them over again the right way.