Grout Cracking Floor Tiles
Sharon's bathroom floor tile grout is cracking in her Anchorage, AK home. You're not going to believe the photos. Here's her story:
"My master bath floor has cracked and chipping grout in more than 50 percent of the tiled area.
Some tiles sound hollow underneath. The sub-flooring is 3/4 in OSB with 3/8 inch interior plywood on top of that.
We also have Nuheat electric floor-heating mat underneath the tile.
The builder and contractor said the reason for the cracking and chipping grout is because of the heated mat. Is this true?
We heard a loud crack before the warranty was up, but the cracking started after warranty period. The house is 3 1/2 years old.
Please look at these photos and tell me what you think."
Sharon, your photos are excellent. They communicate to me the skill level of the builder and the tile setter.
It's possible both of them were asleep at the wheel during this job and they maybe used some sort of liquid skill enhancer in their bodies to try to make up for their natural abilities.
Let's talk about the Nuheat floor heating mat first. I've got one of those in my ham radio shack and they're amazing. I can tell you that if you install the mat per the written instructions and you float over the top of the mat the layer of thinset to produce a surface ALL IN THE SAME PLANE, then you'll have a toasty warm floor and no grout or tile failure.
The OSB and plywood are sufficient to support the tile, assuming the floor joists are stiff and the floor is NOT SPONGY. The wood floor system must be very stiff.
Your second photo tells the tale as far as I'm concerned. The bed of thinset is thick, it's not even and there are voids under the tile.
Ceramic tile should NEVER have voids under it. Tile is very strong in compression, but usually only has 10% of its compressive strength when you put it under tension. Tension is a stretching or pulling force. This happens when you step on a tile that's hollow under it and it *stretches* to try to support your weight.
In almost all cases, the tile snaps and cracks.
When tile moves like this, it causes the grout to crack too. Grout is also weak when you subject it to tension.
It's also possible the installer used too much water when he mixed the grout or when he finished the joints. In either case, the excess water dilutes the Portland cement in the grout making it weak.
I'm afraid to tell you that the tile needs to come up, you need to put a thin coat of thinset down over what you have and get it all in the same plane so there are no humps or dips.
Then you install the tile as I demonstrate in all my past ceramic tile installation columns and videos. Watch them!