Installing Ceramic Tile Over Tile Floors
Thinset Mortar Selection
Install tile using a latex modified thinset mortar or mix a standard non-modified thinset mortar with an acrylic latex admixture in lieu of water. Always read and follow the manufacturer's product recommendations.
Unsuitable tile over tile surfaces:
Installation over leveled surfaces:
Apply thinset mortar skim coat onto existing tile floor using a wide putty knife or the flat end of your thinset trowel. Make sure to fill in and skim off any depressions you find (e.g. grout joints) to prevent pockets of air from forming under the new tile installation. After the skim coat has been applied you can install the new ceramic tile flooring. We generally recommend that the thinset mortar be applied to the backside of the floor tiles, however, either way is acceptable in many cases.
Installation over uneven surfaces:
Fill in and float off any dips, humps, or waves over the existing tile installation using a Latex-Portland cement based floor leveler. For dips, this product may be used to fill the cavity and screed off using a level or straight edge. For humps, apply the floor leveler around the base of the protrusion. Then, using the top of the hump as a guide, screed the floor around the base of the hump in a circular motion. This will help to lessen the impact the protrusion will have on your finished floor.
Many Portland cement based floor levelers need to cure for at least 24 hours before the tile can be installed. Follow the manufacturer's installation instructions.