TECH TIP: Is Your Floor or Wall Flat Enough for Large Format Tile?

How prepared are you for installing Large Format Tile (LFT) and ensuring you have a surface that is adequately flat? It’s a big deal and worth considering before you get started.

Large Format Tile is growing significantly!

Tile sizes are increasing. Large format tile has grown from the old 8” x 8” to 12” x 12”, 12” x 24”, 24″ x 48″ and beyond. You’ll even find Gauged Porcelain Tile (GPT) and Gauged Porcelain Tile Panels/Slabs (GPTPS) ranging from 1 meter x 3 meters (roughly 39” x 10’) up to 1-1/2 meters x 3 meters (almost 5’ x 10’).

Not only are sizes increasing, but larger sized tiles have been fully embraced by home and building owners and specifiers.

As a result, tile installers must know how to accommodate inherent warpage associated with large format tile, as well as how to provide (and get paid for doing so) a surface that will allow these products to be installed without lippage or at least within the allowable tolerances provided in the ANSI documents.

>> See Do You Have Enough Mortar to Accommodate Most Tile Warpage?

The ANSI Standard for Subfloor Surfaces, ANSI A108.02-, 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.”

How to determine the condition of the floor or wall?

Determining the condition of the floor or wall is relatively easy by using a ten foot straightedge.

Simply mark the substrate with some method such as circling the low spots and placing an X on the high spots to quickly show where the work is needed to meet the ANSI specification.

Then, use a combination of cementitious patching compound (either trowel applied or self-leveling) to fill the low spots and grind down the high spots. This will normally provide a surface that will be suitable for installing tile within the prescribed tolerances.

By the way, you should never use thin-set or large and heavy tile (formerly medium bed) mortars to flatten the surface.

Use a long straightedge to determine if the trowel applied patch is flat enough for large format tile.

Notice in the image above taken during an Advanced Certifications for Tile Installers (ACT) test, how 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 and still be within the lippage requirements.

Realize that the allowable lippage for this tile installation under ANSI Specification A108.02- 4.3.7 is just 1/32” (about the thickness of a credit card).

Before installing large format tile, look at the surface! Is it flat enough?

Before starting your next job, look carefully at the surface that is to receive tile. What will it take to make it flat enough to install large format tile? Identifying how and requesting a change order before the job starts increases your chances of getting paid for the quality work you have provided.

And, don’t even think of trying to “fix” the floor or wall surface as you go with thin-set mortar! That will almost always result in an unsatisfactory finished product.

Do your customer and yourself a favor, do it right… the first time.

Thanks for reading,