Does slate tile have to be laid over hardi-board or can I use mastic over 1/1/2 plywood?

Question

Some slate mfgs. claim their tile can be installed over exterior plywood. I say backerboard.Help?

Answer 1

exterior plywood is fine, but as a tile installer for 12 years now, i would recomend 1/4 inch hardibacker.

Answer 2

I tile every day of my life, over all manner of substrate, Concrete backer board has become somewhat of a standard, for a few reasons, but isn't a strict issue.

   What matters more is the condition of any substrate, and/or what it has been installed over. In your case, and without knowing if the 1.5 Ply is over floor joists, I suspect you'd notice any instability. I have 1.5, doubled ply in a mobile, tiled with Thin Set, that has held up problem free for more than 3 years.

   The claim,,, BTW, isn't false. Tile probably can be installed over almost any substrate. The issue,,,again,,, is the condition of that substrate, and underlying framing. I offer this as an analogy.

   So often here, I see "CAN I?" questions, and answer many of them with, "Certainly" I also usually add, "BUT you may not be totally satisfied."

   In some measure, it depends on the WHERE this install will take place, and assuming the Slate has been "Milled" in a fashion similar to the back of a piece of Ceramic tile. I'm not a fan of mastic on a floor, but I'm sure it's done.

Steven Wolf

Just my two "sense"

  As much an issue for you might be a further, fractional loss of floor to ceiling height by adding another substrate and then the tile. The issue stated earlier (Stable Framing) would still matter, no  matter what substrate you use, or method and substance of installing.

Answer 3

I agree w/ Doc..  As a 20 year tiler I stick to tile codes best as poss and common sense.. Minimum  thickness  in a substrate  can be no less than 1 1/4 inches. Usually 3/4 subfloor and 1/2 cement board but that changes w/ the common sense part. I m not a fan 1/4 inch board at all unless subfloor is thicker etc.16 in oc joists come into play also as opposed  to 24 oc.. I ll never use a mastic because newer mastics stay more plyable and don t dry out .. Cost plays a factor in my useing thinset also(much cheaper) Don t forget to wipe off the backing of any slate since a lot of times slate will have a dusty residue on them   GL

Answer 4

As a contractor, I agree with the answer below.