How to Install Mosaic Tile

Installing Mosaic Tile
Embedding grout is the last major step in installing mosaic tile. LJM Photo/Getty Images

Mosaic tile is a beautiful addition to any kitchen or bathroom. This tile favorite can produce stunning designs when used for backsplashes, shower or tub surrounds, or for walls. But mosaic tile installation can be a bit tricky. In fact, large-tile installation (12 inches square or greater) looks simple once you get into the world of mosaic tile sheets.

One-inch or smaller square tiles (called tesserae, plural) can, surprisingly, make installation quite difficult. In the past, tile installers painstakingly laid each tessera/tile individually. Today, these tiles come attached in fiberglass mesh-bound sheets of 144 individual tiles at a time.

It sounds like it would be easy and fast to set down 144 tiles in a bed of wet mortar, all in one motion. And while it certainly is easier than laying one tile at a time, the reality of the process can be more difficult. 

1. Cut the Mesh Between the Tiles

Tile installation is as much about cutting as it is about laying. However, make every effort to avoid cutting mosaic tiles.  

If you come to an edge and anticipate cutting a long line of mosaic tiles, first see if the baseboard or trim will cover full-sized tiles rather than proceeding to another row of cut tiles.

The way to cut mosaic tile sheets is to leave individual tiles whole and to cut the fiberglass mess between the tiles. If you need to cut a mosaic sheet, the best way to do this is to cut from the back with a utility knife. The fiberglass mesh will easily yield to a sharp utility knife.

If you must cut the mosaic sheet from the top with scissors, it is harder to get a clean cut. You will need to slightly bend the two courses of tiles for your scissors to have enough room to fit.

2. Cut the Mosaic Tiles

You have several options for tile-cutting, ranging from cheap to very expensive. If you are a do-it-yourself installer doing one project, you will not be cutting much mosaic, in which case you can use a rail cutter and a tile nibbler.

The rail cutter (or snap tile cutter, as it is sometimes called) can cut an entire row of tiles by scoring them and then snapping them in half. The tile nibbler (or nibbler) looks like a pair of pliers and it allows you to cut one tile at a time.

A wet tile saw is more expensive, but it will vastly improve the speed and efficiency of your mosaic tile project. If you have several tile projects ahead of you, it may be worth it to buy a tile saw rather than using the snap tile cutter.

3. Lay the Tile in the Thinset

Even though the tiles are affixed to a single sheet, the sheets are flexible and do not keep the tiles within perfectly square. After you have laid down the proper amount of thinset, press down on the mosaic. After you embed the mosaic tile sheet in the thinset mortar, make sure that the tiles within the sheet are properly lined up.

Excess thinset mush matters less when you are working with big, single tiles because you only have four edges to clean. But with mosaic, cleaning out the seams can be difficult and it rarely looks good. Use only as much thinset as your v- or square-notched trowel dispenses, no more.

Unified bundles of mosaic tesserae do not behave the way a single, large tile might behave. Mosaic tiles can warp, wave, shift, and create lippage, making your new tile floor look like an ancient Roman floor, but not in a good way.

Warps and waves are horizontal imperfections that look like subtle ocean waves prior to cresting. Shifts are grout width variations within tile sheets. Lippage is a potentially hazardous feature where one row of tiles is higher than its neighboring row. 

4.  Gently Tamp the Mosaic Into Thinset

Use a small piece of plywood (about 8 inches square) and a rubber mallet to tap down the mosaic sheet into the thinset mortar.

This flattens the tile area, giving it a nice smooth surface. Also, it ensures that the mosaic tile sheet is firmly embedded in the mortar.

5. Spread the Grout

After the mosaic tiles have thoroughly set in the mortar and are in no danger of shifting, mix up dry grout (or purchase pre-mixed grout). Using your rubber tile float, spread grout over the tops of the tiles. Embed the grout between the tiles by keeping the float tilted at a 45-degree angle, so that the edge of the float is doing the pressing.

6. Remove the Grout Haze

A thin, white dry haze is a natural byproduct of grouting. After the grout has fully cured, use a liquid grout haze remover to get rid of this white film.

7. Seal the Grout

Because tile grout is porous, it must be sealed in order to protect the subfloor, as well as the integrity of the tile installation.