CTEF Tile Tip: Installing Large, Thin Tiles: Is the Surface Flat Enough?

During an ACT test, an installer uses a straightedge to see if the surface is flat enough to accept tile.

It goes without saying that tile sizes are increasing.Large-format tile (LFT)has grown from the old 8” x 8” to 12” x 12”, 24” x 24” and beyond. The new thin porcelain tile (TPT) can be 1 meter x 3 meters (roughly 39” x 10’) up to 1 1/2 meters x 3 meters (almost 5’ x 10’). Larger-sized tiles are here to stay and installers need to provide (and get paid for ensuring) a surface that will allow these products to be installed without lippage, or at least within the allowable tolerances provided in the ANSI documents.

ANSI A108.02-4.1.4.3.1 states in part: “For tiles with at least one edge 15” or longer, the maximum allowable variation is not more than 1/8” in 10’ and no more than 1/16” in 2’ from the required plane, when measured from the high points in the surface.”

Determining the condition of the floor or wall is relatively easy by using a 10’ straightedge. Simply marking the substrate with some method such as circling the low spots and placing an X on the high spots quickly shows where work is needed to meet the ANSI specification. Using a combination of cementitious patching compound (either trowel-applied or self-leveling) to fill the low spots and grinding down the high spots normally will provide a surface that will be suitable for installing tile within the prescribed tolerances. By the way, thin-set or large and heavy tile (formerly medium-bed) mortars should NEVER be used to flatten the surface.

As seen in the attached photo taken during a recent Advanced Certifications for Tile Installers (ACT) test, the installer is using a long straightedge to determine if the trowel-applied patch is flat enough to receive a 12” x 24” porcelain tile with a 1/8” grout joint to be within the lippage requirements. Realize the allowable lippage for this tile installation under ANSI Specification A108.02- 4.3.7 is just 1/32”.

Before starting your next job, look at the surface that is to receive tile and understand what it will take to make it flat enough to install the tile. Requesting a change order before the job starts increases you chances of getting paid for the quality work provided. Attempting to “fix” the floor or wall surface as you go with thin-set mortar will almost always result in an unsatisfactory finished product. Do your customer, and yourself, a favor. Do it right…the first time.

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.