Q. Can I install new tile over old tile for a bathroom floor?
A. Tom Meehan, a second-generation tile installer and co-author of Working with Tile who lives and works in Harwich, Mass., responds: Putting new tile over old is possible if the work is done properly and if the condition of the existing floor—both the tile itself and the subfloor below—is in good enough shape for a successful installation. You also need to consider that adding another layer of tile will increase the height of the floor, which can create complications with bathroom fixtures, thresholds, and doors that swing in.
The first and most important question is whether the existing tile floor is structurally sound with no loose tile or major cracks. A visual inspection for cracked or missing grout is a good initial check for possible loose tile. Another way to check is by tapping on the surface of the tile with a small hammer. Hollow sounds can be an indication that tiles may be loose. If I find one loose tile, it usually means that others are loose, so in that case I typically remove all of the existing tile rather than risking problems with an added tile layer. Grout missing or large cracks in the middle of the floor can also indicate loose tile, but a little grout missing near the edges of the floor usually means that the floor is OK to tile over.
Cracks running through the tile can also indicate excess deflection in the subfloor. The Tile Council of North America (TCNA) offers strict guidelines for deflection in its handbook. But if the bathroom is over a basement, I’ll often inspect the floor framing from below to look for cracked or broken floor joists or improper joist spacing. When in doubt, I sister in new joists to the old to beef up the framing.
To install the new tile over the old, I have one of two approaches, depending on the condition of the tile. For both approaches, I start by scarifying or abrading the surface of the old tile with a grinder outfitted with an aggressive diamond blade. This removes most of the glazed surface from the tile and gives the thinset a better chance of adhering. Then I vacuum and sponge off the surface of the tile.
When the floor is dry, I apply a tight (1/16 to 1/8 inch thick) skim coat of high-quality latex-modified thinset, such as Laticrete 254 Platinum, and let this skim coat sit overnight. If the floor is solid with no cracks or missing grout, the next day I install the new tile over the prepared floor the same way I would tile any other floor, using a high-quality modified thinset, which adheres best in these applications.
If the floor has hairline (nonstructural) cracks in the tile or grout, I install an uncoupling membrane, such as Schluter’s Ditra, over the skim coat of thinset. The membrane bridges any cracks, preventing them from telegraphing up through the surface of the new tile layer. I install the membrane over the dried skim coat that I had applied to the scarified tile, using the thinset recommended by the membrane’s manufacturer. After letting the membrane set overnight, I install the tile the next day.
If you have any doubts about the integrity of the old floor or your ability to assess the floor’s condition, I’d go with the membrane approach. The little bit of extra work and expense is cheap insurance that the new tile floor will not develop any problems in the future.
