Tile and its accessory materials like thinset mortar or grout cannot flex.
That’s why mitigating materials like cement board are important for tile installed on flex-prone wood floor systems.
But what about when you already have a hard and solid masonry base in the form of concrete?
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Is it necessary to install a layer of cement board between the tile and the concrete?
If not, what is a better solution?
James Hardie Industries: HardieBacker
HardieBacker specifically excludes concrete as a base for installation.
The floor should meet or exceed L/360 (tile) or L/720 (stone) deflection criteria.
L/360, L/720
L/360 and L/720 are deflection requirements for floor rigidity.
For a 24-inch span, this translates to a deflection maximum of 0.07-inch.
Tile Professionals' Recommendations
Manufacturerprohibitions or omissions are warranty issues.
The questions remain: Can you effectively pair two cementitious productscement board and a concrete slab?
There is no problem with the two materials being compatible.
A powder-actuated nailer is out of the question since nail depth would be impossible to regulate.
Concrete screws, Cline says, have heads that are too small to hold down the cement board.
Portland cement-based fillers can take care of holes and cracks.
Painted concrete can be sandblasted, sanded, or ground down to bring up a nice, porous surface.
Thinset alone will not help the cement board stick to the concrete slab.
These mats are now standard for preventingtile installed on concretefrom cracking over time.
Minor changes in the concrete are not transmitted to the tile and thinset above.
Major changes in the concrete are mitigated, reducing the likelihood of cracking.
Deflection.Tile Council of North America, Inc.
