Floor thickness [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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10-05-2006, 07:01 AM
I am about to start laying hardi (or cement board) and had a question about overall floor thickness. I am trying to add 3/4" (total- hardi, warming wires and tile) so that the bathroom floor ends up being the same height as the hardwood in the bedroom. The tiles we picked out are 3/8" thick. I want to use 1/2" hardi but by the time I get the tile and wires in I am looking at well over 3/4." Is 1/4" hardi ok to use? Does anyone make something that is 3/8" thick? The subfloor is new construction 3/4" T&G OSB on 2x10" 24" O.C. The deflecto gives me a 571. Does the hardi change that?
Thanks in advance.
Alexis Roccos
Columbus OH

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10-05-2006, 08:32 AM
Alexis, I see a slight problem here. Well...maybe not so slight. No backerboard manufacturer that I know of will recommend or warrant their product for use over joists spaced 24" OC. So what that leaves you with is a membrane type of solution, like Schluter Ditra. However that method requires a double layer plywood floor with 3/8" minimum on top of what you have now.

I won't take this any further for now. But it is time to step back and rethink your installation plan along with preparing for some type of height transition between your tile and hardwood flooring.


10-05-2006, 08:36 AM
Alexis, 1/2" backerboard is for walls. 1/4" board is for floors that meet the manufacturer's specifications. Unfortunately, your joist spacing is too far for backerboard. It's also too far for membranes, unless you add some more plywood first.

Let's look at another approach: If you used Ditra for your underlayment, you'd have to install 3/8" plywood, your heating mats, then the Ditra and finally, yoiu tile. This will cause your floor to be about 1" higher than the current subfloor (maybe a tad higher). This will be about 1/4" higher than the hardwood. You can live with that transition as-is, or include a wooden (or metal) transition strip, or you could add a 1/4" underlayment under the hardwood to make everything come out even.