If your entry has wood subflooring, shore up the joists and the subfloor, if necessary, and prepare the surface with the same methods used for a slab. Mix enough thinset to allow you to use it within its working time (the time it takes to “skin” over) and trowel it on the floor, smoothing first with the straight edge of a trowel and combing it with the notched edge. Screw down cement backerboard with the edges centered on the joists, offsetting subsequent joints and spacing the edges ⅛ inch apart. Drive screws into the backerboard on the edges and within the field. Tape the backerboard joints with 2-inch pregummed tape and spread a thin coat of thinset over the tape. Tile floors expand and contract with changes in temperature. Expansion joints cushion the expansion of tile against the wall and keep the tile from cracking. An expansion joint is a gap filled with a compressible material and topped off with caulk. Foam backer rod is available in a variety of thicknesses. Purchase backer rod that fits snugly. On a slab, insert foam backer rod into any control joints in the field of the slab and also along the perimeter at the wall. Push the backer rod into place with a wide putty knife. On a wood subfloor, insert the backer rod into the ¼-inch gap between the cement backerboard and the wall. Finish the joint with caulk colored to match the grout.
