Can I Apply Mortar on Top of Tile Adhesive?

Mastic

• Mastic is the tile adhesive that you may run into if you attempt to install a tile floor over an existing floor. Mastic is a thin glue created from the resin of a tree that forms a sticky paste for setting tile. Tiles that have been set with mastic can either be removed or tiled over. However, if you decide to tile over this adhesive, there are some considerations to keep in mind. The first of these is the fact that the existing tile floor needs to be level and in good shape beforehand. Secondly, you don't want to install over mastic if you are in a high moisture area. Because this is a natural tree resin, it can potentially attract and grow mold.

Mortar

• Mortar is typically used to install most tile floors, although the development of tile adhesives has led to some contractors moving towards using these whenever possible. Adhesives offer an advantage as they can be used to install a tile floor over a plywood subfloor. This is not typically possible with mortar because of its wet nature. Mortar can be directly applied over a tile adhesive, such as mastic, but the mastic needs to have dried smoothly enough that the mortar can be spread thin and form a bed for the new tile.

Locations

• Installing mortar over an existing adhesive is not usually the best idea if you can avoid it altogether. Instead, determine where you will be installing the tile and what adhesive is most appropriate. Typically, tile adhesive is best used for kitchen backsplashes and walls, or for other walls in rooms where there is no moisture present. Mortar is better for bathrooms and showers because mortar will actually create a barrier for the moisture. It is not fully waterproof, but it is not water soluble as tile adhesive tends to be.

Considerations

• If you decide to tile over an existing tile floor, you have to keep in mind the fact that this will raise the height of your floor. In many cases, the addition of mortar and tile will create a floor that sits about 3/8 inch higher than the previous floor. This does not generally create any major problems, but it may require that you take off the existing door and trim it to accommodate the new height.