Cracking Grout - Is this normal?

8 years ago

last modified: 8 years ago

Tile flooring was installed in an infrequently used bathroom 3 years ago. Just about all of the grout lines have cracked. Is this normal? Will it cause problems? Fusion Pro grout was used. Tiles were installed on top of 1/4" cement board screwed into subfloor.

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SJ McCarthy

8 years ago

Not normal. Cracking grout is a good indication that the SUBFLOOR isn't "stiff enough". And to be clear, cement backer board does NOT add stiffness. It just doesn't. Plywood does. Backer board does not.

The thickness of the subfloor BELOW the cement board will tell you if you have a deflection rating (how stiff the subfloor is) that is required for tile. I'm going to guess the subfloor was built to handle sheet vinyl or something equally light.

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Comments (6)

User
8 years ago
last modified: 8 years ago
Structural, or too much water in the grout mix, over washed grout.

Did the installer discuss deflection with you? Did the installer place thinset under the cement board? Did the installer rush through the job?
torreykm thanked User
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millworkman
8 years ago
I don't believe 1/4" cement board is even rated for floor use?
torreykm thanked millworkman
Chessie
8 years ago
last modified: 8 years ago
1/4" Hardibacker is under the tile in both of my bathrooms. No cracks.

This is right from the Hardiebacker website:

We recommend 1/4” HardieBacker® board for floor applications, unless 1/2” thickness is needed for transition.
torreykm thanked Chessie
torreykm
Original Author
8 years ago
last modified: 8 years ago
Thanks all for your response.....

SJ McCarthy - You are correct. Vinyl flooring was previously installed on 1/2" plywood.

Sophie Wheeler - Grout was premixed. Yes to thinset between plywood and cement board. We discussed the subfloor with tile contractor and GC; both assured me there was no problem with deflection. I was very concerned about that because the tiles are large format/rectified (also very expensive) and we didn't want problems down the road. I wouldn't say the job was rushed.

millworkman - I ok'd the 1/4'' cement board (no, I'm not a pro) because of height. The tiles were pretty thick and I didn't want a large transition in the doorway.

Total coverage was only 55" x 57".

The grout joints are 1/8" so the cracks are only visible if you're a couple of inches from the floor. I wanted to do a little scrub down of the grout when I noticed them.

Should I just keep an eye on it for now? The bathroom is rarely used. Should I have the hubs go under the house, check the joist spacing and see if the substrate was suitably prepped?
User
8 years ago
If you are not exposing the floor to water, I think you are ok.

Based on your floor conditions, your substrate was not suitably prepared.
torreykm thanked User