This story shows how to prevent tile floors from cracking by properly preparing a wood subfloor.
After you have removed or repaired the existing surface of the floor, turn your attention to the subfloor. Ceramics and stone must be kept from cracking and all subfloors should not squeak or sag. Inspect the subfloor and make repairs that will assure it provides a solid, stable bed.
Dimensional lumber -- 1x4 or 2x6 planking -- is not suitable as a bed for any tile. Planks expand and contract with changes in temperature and humidity, as does tile, but at different rates. The result is cracked tile, broken grout joints, or split seams. Install plywood or backerboard on plank. If the resulting floor will be too high for smooth transitions to adjacent floors, tear up the planking and install 3/4-inch exterior-grade plywood, followed by backerboard for ceramics.
About 30 minutes to check defects in an average-size room. Repair time will vary with size and condition of floor; could average 45 minutes per square yard.
Repair subfloor: 4-foot level, cordless drill/bits, hammer, circular saw Repair surface: mason's trowel, belt sander, nail set Installing membrane: roller, trowel
Driving nails with hammer; removing fasteners with cordless drill; sawing with circular saw; troweling with a belt sander
Remove or repair finished flooring
Subfloor: 2x4 lumber, 2-1/2-inch coated screws, 8d nails, wood shims Surface: thinset mortar Installing membrane: membrane, adhesive
If the entire subfloor is weak, cut 2x4 bridges to fit between the floor joists. Measure the joist spacing across the floor and, if the dimensions are equal, cut all the bridges at one time. If the spacing varies, cut the pieces to fit. Nail the bridges in place, offsetting each one by 24 inches.