Revised January 10, 2005
Back-Mounted Ceramic Tile
Prior to the early 1950’s, all large unit tiles, 4 ¼“ x 4 ¼” and larger, were installed individually. Mosaics up to 6 square inches, including glass mosaics, etc., were face mounted on 1´ x 1´ or 1´ x 2´ sheets at the factory by applying paper to the outside face of the tiles with a water soluble adhesive. When the tiles were set conventionally in a fresh mortar bed after back buttering the sheets with a grout mix, the paper could be removed by brushing the surface with water, and the paper stripped off easily. Any glue or paper left on the surface of the tile could easily be washed off without disturbing the bond of the tile to the setting bed after allowing enough time for the initial set to take place but prior to its final set.
With the advent and expanded use of thin-bed materials, face-mounted tiles became difficult to use on the job and required special care and skill to install. The need for a faster setting method became more apparent, especially as labor costs rose and the popularity of mosaic tiles increased. Perforated paper, jute material, nylon mesh, rubber and many other products were used as mounting materials and applied by factories to the underside or back of the tile. This permitted the mechanic to install sheets of tile rapidly, observe his work thoroughly, and make any corrections immediately (such as replacing cracked or broken tiles).
Failures have occurred through the use of back-mounted tiles. In many cases thin-bed adhesive bonded to either paper or a thin layer of water soluble glue on the back of the tiles, with no contact made to the tiles themselves. Water eventually soaked through the portland cement grout joints, and rewet the mounting glue sufficiently to break the bond and cause a failure.
In other exterior failures, water penetrated to the back-mounted paper and wicked behind the tile, and when the installation froze, the bond was broken.
Rubber dot mounting made sheets of back-mounted tile less flexible than the face-mounted tile. Proper beat-in of these sheets into Latex Portland Cement Mortar is essential to prevent loss of bond. Back buttering of tile where tile thickness is 3/16 of an inch thick or thinner may be necessary to assure proper contact and support of this type of material.
The ceramic tile manufacturer shall be responsible for mounting the tiles so that the bond requirements of ANSI A137.1 (50 psi) according to ASTM C482-68 are met or exceeded. Tile manufacturers shall be responsible for specifying where their mounted tile assemblies shall be used.
We strongly urge all ceramic mosaic tile manufacturers to clearly indicate on their cartons, in the cartons, or on each sheet of tile, whether or not their mounted tiles are suitable for use in swimming pools, exteriors, or other wet areas.
Mounted tile is described in the current ANSI A137.1 and Tile Council of North America’s Handbook for Ceramic Tile Installation. MMSA members recommend the installation of labeled ANSI A137.1 mounted tiles according to ANSI specifications. Manufacturers and distributors of both domestic and imported tile must give assurance that the same test requirements and conditions shall be obtained. Only by following specified procedures can we be assured of trouble free, long lasting installations.