CTEF Tile Tip: The Right Coverage Under Large-Format Wall Tile

comb mortar parallel to short side of tile

Make sure to comb the mortar parallel to the short side of the tile, so the trapped air underneath has a shorter distance to travel.

Many projects today call for ever-increasing tile sizes, many of which are rectangular shapes such as 12" x 24", 18" x 36", 24" x 48" and larger, creating difficulties for the installer when bonding the tile to the substrate. Most times obtaining acceptable coverage on the floor is not as difficult since the installer’s weight can be used to help collapse the trowel ridges into the valleys while moving the tile back and forth, as shown in NTCA’s Trowel and Error video (https://www.youtube.com/watch?v=fNOjZrs5Xr4). However, when these same tile sizes are installed on wall surfaces, obtaining the required coverage becomes more difficult.

These larger tiles can be cumbersome to handle by one installer and can be challenging to move in the back-and-forth motion. The installation can be further complicated by the job requirement of narrow grout joints. These narrow joints do not allow the tile to be moved more than this width, which may not collapse the ridges.

There are several ways to help achieve the required mortar coverage:

Most importantly, always check the flatness of the wall with a 10' straightedge. Remember that for tiles with any side longer than 15", the flatness requirement as noted by ANSI is 1/8" in 10'. Flattening the wall with the appropriate flash patch to meet this requirement will make the installation much easier.
After properly keying the mortar into the substrate with the flat side of the trowel, change the direction of the straight line troweling method. Whichever way the tile is being installed (vertically or horizontally), comb the mortar parallel to the short side of the tile so the trapped air under the tile has a shorter distance to travel. For example, if a 12" x 48" tile is being installed, the mortar ridges should be in the same direction as the 12" side, as seen in the attached photo.
Use suction cups applied to the face of the tile. Two suction cups will provide a “handle” on each side of the tile, which makes moving the tile back and forth more easily accomplished.
Consider using a trowel that has deeper and narrower notches such as a 1/4" x 1/4" x 1/2", a “U” notch such as a 1/8" x 3/4" x 1/2" or a zipper notch. This way the tile needs only to move a short distance each way, yielding better coverage.

As you’ll see, a couple of small changes in technique can really make a difference.

Scott Carothers is the Director of Certification and Training for the Ceramic Tile Education Foundation headquartered in Pendleton, SC, and is responsible for the creation of the Certified Tile Installer (CTI) program, is involved in the creation of the new Advanced Certifications for Tile Installers (ACT) program as well as providing training to others in the tile industry. He has been involved in the ceramic tile industry for over 33 years and was the owner of a successful retail firm prior to coming to CTEF. He has served as President of the NTCA, Chairman of the NTCA Technical Committee and named the NTCA Tile Person of the Year in 2005. He is a voting member of the ANSI and the TCNA Handbook committees. He may be contacted at 864-222-2131 or scott@tilecareer.com.