bathroomconcretemortarscrewstile
I am installing hardiebacker concrete board with thinset to a plywood subfloor.
I am putting down the new subfloor and want to be sure the screws that I use to secure the plywood to the joists will not corrode from the layer of thinset over the subfloor.
All the floor screws I could find in the box stores are black phosphate screws. Are these black phosphate screws alkali resistant and will they be OK in contact with a layer of thinset and cement board on top of the subfloor?
Would like to put in a suggestion for either Schluter Ditra or Laticrete Strata-mat.
As uncoupling membranes, they effectively stiffen floors by unitizing the tile layer. For stone installation, Schluter recommends double layer of underlayment. The second layer should be offset from the first layer, not following seams. The second layer should only be attached to the first, not through to the framing. The total thickness only has to be 3/4, but can be thicker as necessary for level matching. The first layer should be at right angle to the joists, along the the long direction of the ply.
Ditra stone tile install
Ditra plywood install
excerpted from Ditra installation handbook
Here is an idea to consider. If the tile comes off the cement board fairly easy, you could leave the cement board, scrape off the thinset and lay your foam and laminate over the cement board. Just a thought depending on the overall thickness you need to achieve.
Best Answer
Phosphate offers no more protection than galvanized or paint coating ; The good news is once the thinset cures ,they will always be dry so corrosion won't be a problem.