Mosaic tiles are gaining in popularity, yet some installers shy away from the work. In most cases, this is the result of a bad experience with adhesive squeezing upwards, filling all the grout joints, and creating a nightmarish cleaning task (Photo 1). Installing ceramic, glass, and stone mosaics can be enjoyable, interesting, and profitable work for any installer who can do it well.

As anyone who has ever visited the Old World knows, mosaic tiles are a part of human history that date back thousands of years. That they still exist today is a testament to the durability of the bits of glass and stone that comprise most mosaic compositions. Mosaics can be done bit by bit, but even a thousand years ago, most mosaic bits were grouped together in modules that were mounted on a paper or cloth sheet.

Mounting (Photos 2 and 3) is an important aspect of mosaic installation because the mounting may sometimes interfere with - and reduce - the adhesive bond between the mosaic bits and the setting bed. Mosaic generally means tiles smaller than two inches. Because individual tiles on a mosaic sheet are so small, practically any interference is disruptive.

For this reason, face mounting offers a completely open back, and the potential for maximum adhesion (Photo 4).

Mosaics are made from bits of ceramic tile, stone, glass, and a variety of other hard materials. Practically any material can be used to create a purely decorative, non-functional mosaic composition, although not all mosaic materials are suitable for use on floors or other functional areas. Although the tiles shown in the photos are all rated for use on floors and in wet areas, some ceramic, glass, and stone tiles are not. Ceramic, glass, and stone tiles have different properties, and each example may have different installation requirements. Before attempting any mosaic work, consult the tile manufacturer's installation brochures and installation material recommendations; depending on the mounting and type of mosaic bit, installation instructions are sure to vary.

The methods and techniques shown here are not meant to cover every possibility, but instead are intended to show, in a general way, how various mosaic sheets can be installed. In all cases, a white latex-modified thinset mortar, as recommended for use with ceramic, glass, or stone bits, is used to install the mosaic sheets. It is possible to use gray latex thinset on glass tiles, but gray dulls the color of the glass, and is usually not recommended. A beating block and hammer are used to seat all the mosaic tiles, but these tools must be used gently when working over hard setting beds to avoid breaking any tiles.

Spreading Adhesive Mortar for Mosaic Tiles
The notched trowel is used by installers to apply a uniform amount of adhesive under tiles. A consistent amount of adhesive is necessary for the tiles to sit in a smooth, even plane. A uniform amount of adhesive is especially important under mosaic tiles since their small size tends to accentuate irregularities on the setting bed. As well, because mosaic tiles are usually thinner than regular tiles, even a small amount of excess adhesive can clog up the grout joints and create a nightmarish cleaning job.

In Photo 5, a single sheet of porcelain mosaic tiles is installed over thinset mortar. The photo shows the upper half of the mosaic sheet being supported by adhesive ridges while the lower half is set over a flat bed of thinset. What the photo does not show is that the amount of thinset under each half is identical: the only difference is that the adhesive ridges on the lower half have been flattened by the smooth edge of a trowel. As you can clearly see, the grout joints in the upper half of the sheet are clogged with thinset, while the lower joints are clean and ready to grout (after the thinset has cured).

As with all tile installations, the correct-size notch trowel to use is determined by site-testing different-size trowels to achieve 85-percent minimum coverage for dry-area applications and 95 percent for wet areas. To install the 1-inch glass mosaic sheets, I used a manufacturer's recommended trowel: a 3/16-by-1/4-inch V-notch trowel.

The technique displayed here can be used for any other type of paper face-mounted mosaic sheets. First (Photo 6), thinset mortar is spread conventionally using the smooth edge of the trowel to distribute the mortar, and then the notched edge of the trowel is used to create full, uniform ridges (and an even dispersal of the mortar). After the area to receive tiles is combed with the notches, the smooth side (Photo 7) of the trowel is again used to lightly flatten the ridges.

Bedding the Mosaic Sheets in Thinset Mortar
Once the adhesive has been spread, it is important to get the mosaic sheets bedded in the adhesive as quickly as possible (Photo 8). I use my hands (Photo 9) to smooth the sheets and feel the joint where two sheet edges meet; the lippage detected by my fingers help me gauge how much beating block to apply.

The beating block and hammer are ideal tools to use when working over a bed of soft, fresh mortar (Photo 10). When working over hard setting beds, however, an installer has to be patient and gentle to avoid breaking any mosaic bits: according to industry standards, there should be a minimum of 3/32 inch of thinset mortar between a tile or mosaic bit and its setting bed.

Removing the Paper Face
Before installation, all paper face-mounted mosaic sheets should be inspected for uniformity and regularity to ensure that all the mosaic bits are aligned properly. In spite of this precaution, though, the mosaic bits should be inspected again once the sheets are installed. To do this, dampen the paper mount with a moist sponge, keeping 100 percent of the paper damp for about five or 10 minutes, or until the paper can be gently removed. Start at a corner and peel the paper away (Photo 11). If mosaic bits lift off the setting bed, the paper needs more soaking. With the paper removed, any last-minute adjustments can be made. After that, the mosaic bits should be allowed to rest for at least 48 hours before the paper-mounting adhesive can be scrubbed off the surface of the tiles and the installation can be grouted.

Plastic Film Mounting
Plastic film is a form of mounting that permits the installer to keep all the tiles and bits in a mosaic sheet in view at all times. The layout for the irregularly shaped mosaic sheets here (Photo 12) is done by positioning the sheets dry and outlining the perimeter with an indelible marker. The mosaic sheets are then stacked in a convenient location to await installation. For spreading an adhesive layer of thinset mortar for these mosaic sheets, I used a 1/4-by-3/8-inch square-notch trowel and, following the same procedure I used on the glass mosaic sheet, finished that process by flattening the adhesive ridges just before installing the mosaic sheets.

Bedding the Sheets in Thinset Mortar
When the adhesive is ready, the first sheet is placed gently over the adhesive bed. When the second sheet is installed (Photo 13), I dip one corner to mate the sheet with its neighbor's edge, lay it gently into the adhesive, and make any adjustments to ensure the remaining sheets align with the outline marks (Photo 14). When all the sheets in the area I am working are installed and properly aligned, I use a beating block and hammer to gently press each mosaic bit into the thinset mortar and ensure that the surface of neighboring sheets is smooth and even (Photo 15).
Removing the Plastic Film
Prior to installation, any loose mosaic bits should be pressed back into the plastic film. Once the sheets have been bedded in mortar, they should remain undisturbed for at least 24 hours before an attempt is made to remove the plastic film - earlier if a rapid-setting thinset is used. Grouting can proceed as soon as the film is removed.
Installing Back-mounted Mosaic Sheets
Back-mounted mosaic tile sheets should be installed over an adhesive bed that is prepared using the same spreading and flattening techniques employed for face-mounted sheets. Unsuitable or unwanted mosaic bits (removed to make way for a design or pattern) should be cut away from the sheet before it is installed, and the beating block and hammer should be used to keep the surface flat.