I have an old house that's built on pillars and has shifted a little over time. We are remodeling the kitchen and just ripped up many layers of creatively installed flooring. We are down to the bottom layer of plywood and it dips on one side of the room (8"x 15" room) and then kind of comes back up.
We aren't sure how to tell how sloped it is or how much leveling is really necessary. We have heard that if we don't level it the tiles will eventually crack so we want to prevent that.
We are planning on putting down backer board in between the plywood and the tiles, will that be enough support or is it important to do some sort of leveling first? If we level with something like cement will we need another layer of plywood or can we put the backer board right on top?
Any advice appreciated, thanks so much!
Best Answer
You did hear correctly: the floor must be as flat as possible (and as rigid) in order to support the tile. You mentioned the floor being supported on posts. If there is enough head room a better repair is to shim-up the low spot from below. Depending on how severe the floor depression is this may entail hammering some store bought shims under the joists or installing concrete footings so as to support new posts.
The quick easy solution is to outline the low-spot of floor , mix-up a bag of self leveling floor mix, and trowel it into the depression feathering the edges.
It would also be a smart idea to check the other sections of floor that will get covered by tile for any squeaks, bounce or shifting. Nail or screw to secure them to joists.
When you are ready to begin installing the cement board it would be wise to embed the 3' x 5' x 1/2" cement boards in a thin slurry of thinset for complete support. Use cement board screws to affix them to the floor.