I’ve decided to lay the floor tile before reinstalling the family room bathroom toilet and sink. I don’t really want to install them and then later take them out again to tile. Why not tile first? The question was whether to use an underlayment on the concrete or not. Ordering the substrate delays starting the project and adds extra cost.
That bathroom floor has several cracks in it. I’m not sure whether the bigger shower and its thinner concrete has caused more cracking or if it is just a weak area for some other reason. In the upper right corner I have one of the tiles I am using laid out. It is hard to tell it from the stained concrete floor.
There is even a crack that went through the base of the toilet when it was installed before the walls were up or drywalled. We took it out to finish the drywall.
The toilet crack made me believe that if the floor continues to crack, the tile will also crack. I’m using Schluter products in the showers and it seems like a good preventative to use the Ditra uncoupling membrane on this bathroom floor.
This layer is mortared into place first before the tile is set. The Schluter site explains how the membrane works to minimize or eliminate cracking even on OSB plywood.
DITRA provides uncoupling through its open rib structure, which allows for in-plane movement that effectively neutralizes the differential movement stresses between the substrate and the tile, thus eliminating the major cause of cracking and delaminating of the tiled surface.
I chose to order the Ditra through an ebay site because it appeared to be the most convenient way to get it, although it is about the same cost at our local big box store, It is not in stock and would have to be shipped to the store. Big box stores take as long or longer to ship to store or home as online stores.
So I can lay out the tile and cut pieces but wait to install it until the membrane arrives.