Back-buttering and mortar contact: Two distinct processes

Ceramic tile installation requires careful attention to tile bonding. We tend to judge a given job on the final appearance, but the most vital part of the installation is below the tile. It is very important to complete an adequate surface preparation as indicated in our Reference Guide RGT0309, “Surface Preparation Requirements,” available here.

Then, it is essential to choose a notched trowel with sufficient depth to achieve greater than 80% mortar contact with both the tile and substrate for all interior applications, and greater than 95% for exterior installations, commercial floor and wet applications. Trowel ridges must run in the same direction. Place the tiles firmly into the wet mortar, sliding them back and forth in a direction perpendicular to trowel lines, to collapse the mortar ridges and to help achieve maximum coverage. Ensure proper contact between the mortar, tile and substrate by periodically lifting a few tiles to check for acceptable coverage.

  

What is back-buttering?
Today, the tile industry is mainly focused on porcelain tiles. It is strongly advised to back-butter tiles, especially large-format tiles and porcelain tiles. Back-buttering consists in applying a thin layer on the tile backing using the flat side of the trowel. A porcelain tile has a very low absorption rate (0.5% or less), and back-buttering allows the mortar to penetrate the pores of the tile to ensure proper bond.

CAUTION!
Back-buttering does not guarantee sufficient contact under tiles. We have witnessed faulty installations where tiles had been back-buttered, but contact achieved was only 50 to 60% in a commercial site requiring minimal contact of 95%. If tiles are not pushed back and forth in a direction perpendicular to trowel lines, contact will be insufficient.

  

There is a right and wrong way to tiling; be one of those using the right method. Now that you know how to have successful ceramic or porcelain tile installations, you simply need to enjoy your flooring, fully and for years to come.
 
Have a good installation!