Installing Ceramic Tile Over Tile Floors

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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:

Bright glazed (glossy) ceramic tiles. Tearout and replace or install proper underlayment.
Fractured or cracked tiles. Tear out damaged tile and/or install proper anti-fracture protection membrane.
Loose tiles should be removed and the voids filled with an appropriate floor leveling agent or filler.
Subfloor deflection must not exceed L/360 of the span.
Existing ceramic tile floor should be thoroughly cleaned to remove all greases, soap scums, waxes, sealers, etc.
Lightly sanding the surface of the existing tile floor will greatly improve the mechanical bond of the thinset mortar you will use to install the new floor covering to the old.

Skim coat thinset mortar over floor to improve mechanical adhesion & to fill dips in grout joints and tile facing. Install ceramic tile. In this example we are back buttering each tile with thinset mortar..

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.

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