Concrete Interior Tile Subfloor Install Question
HiHoHiHo
| Posted in General Discussion on
I have new construction 7/8 large profile concrete paver floor tiles installed, and they are cracking with long runs, as is the grout. (The cracks coincide and run along the subfloor joints.) The joists are correct 16 oc I believe. So I don’t think its a deflection issue. The tile was laid on Advantech OSB 3/4”, 1 layer, with a Prodesco uncoupling membrane. My GC says this is perfectly fine installment and standard ASTM.
Any tile engineers or professionals want to chime in here because I’m at a loss of what to do. I’ve read the ASTM guildelines, I’ve researched, called the Tile Council, the manufacturer. GC is saying it’s a problem with the tile not the installation.
Replies
Define "large profile" please? The underlayment is only 3/4" total? That's not enough for any tile in my book and certainly not a big tile. The fact that the tile and grout are both cracking means it doesn't have enough support.
Random pattern. Largest is 24 x24”.
Try asking around on the John Bridge tiling forum: https://www.johnbridge.com/vbulletin/index.php
If the pavers are cracking, the floor is moving.
Concrete floor tiles are brittle. Unless the tile manufacturer says otherwise, I would treat it like a natural stone installations with a maximum deflection of the floor as L / 720 or better.
What size are the floor joists, and what is the span between supports?
The longest span is 15’. 16” oc. Contacted the I joist manufacturer and maximum deflection is .20” but more consistently .14”. Does that make sense?
We would need the loads used to calculate that deflection for it to make sense. Tile, stone and concrete floors can be much heavier than the usual wood or carpet finishes.
The other problem with tiles is the relative deflection between the joists when concentrated loads ( like people moving around the room) are applied. This is caused by inadequate support from subfloor stiffness, blocking, cross bracing or strongbacks connecting the joists together. The cracking at the subfloor joints is the result of an poor subfloor installation.
The Tile Council of North America (TCNA) handbook as this to say for stone installations: (page 30, 2019 ed)
"Natural Stone Tile Installations Over Wood Substrates
Two layers of structural wood panels are required on floors to receive stone tile when backer board will be used as the tile substrate. The MIA (Marble Institute of America) prohibits installation of stone tile over single-layer wood floor systems under backer board because of the discontinuity of the system at seams between the subfloor panels. If an unbonded mortar bed will be installed as the tile substrate, a single layer plywood subflooring is permitted."
TCNA method F250 shows the double plywood arrangment. Method F141 shows a single layer plywood with a 1.25" thick mortar bed
The concrete paver installation instructions should identify which TCNA method is acceptable. What does it say?
A link to article on how the double plywood layer should be done:
http://nielsentile.com/articles/position_of_underlayment_to_prevent_cracked_tile_and_grout.pdf
I think your GC is mistaken. The floor is not stiff enough to support the tile. While it may be a standard ASTM method, it is not one suitable for large format stone or concrete tiles.
Thank you for your information.