How To Install Tile Correctly and Get Proper Mortar Coverage

How To Install Tile Correctly and Get Proper Mortar Coverage

Posted by TOA's Blog Team on Jul 20th 2023

Wondering how to install tile correctly? This article will help explain how to set tile the right way so you get proper mortar coverage and avoid failures.

Why Getting Proper Mortar Coverage Matters

As durable as tile and stone are, when they aren't installed correctly with proper mortar coverage, they can break. How you trowel mortar affects how well supported the tile is and how well it can then support heavy loads and direct impact. Essentially, any sections underneath the tile where mortar isn't present become weak spots and vulnerable to failure.

In addition to impact and heavy loading, tiles set without proper mortar coverage are more likely to fail under many conditions! Namely, substrate deflection; shrinkage or creep; thermal expansion in high temperatures; and freeze/thaw applications (less of an issue in Southwest Florida).

Mortar coverage becomes particularly important as tile sizes get larger and longer (think wood plank tile). This applies to any tile with any side 15 inches or longer. What seems to work for small tiles no longer works.

If you're wondering how to get proper mortar coverage, watch the video below from the National Tile Contractors Association (NTCA) titled "Trowel and Error" and read our takeaways. The video demonstrates the correct trowel techniques for setting large format tile, showing how to create a stronger bond between the tile and the substrate. That in turns prevents crack transmission, lippage, tile breakage and other costly tile installation repairs.

>> See Managing Lippage: Why Offsets Matter When Installing Tile

8 Takeaways on How To Install Tile Correctly

Here are our eight takeaways on the Trowel and Error video.

1. Prep your installation surface so it is flat.

This is a point that came up in Learn How to Use the Tuscan Leveling System When Installing Tile: floor prep is critical!

Large format tiles will cover a much larger area of the floor. That means that flatter substrates are needed to successfully set them. According to the Tile Council of North America (TCNA) and the American National Standards Institute (ANSI) guidelines, variations in floor flatness should not exceed 1/4” in 10 feet. For large format tile, there is even less tolerance: variation is limited to 1/8” in 10 feet and no more than 1/16” in 24 inches.

2. Make sure that you get proper mortar coverage on the tile.

Proper mortgage coverage as we mentioned above is critical to preventing failures. According to the ANSI and the TCNA Handbook, tile requires a minimum of 80% mortar coverage in interior applications, and 95% for exteriors and wet environments. Natural stone tile requires 95% coverage in all areas.

Another aspect associated with large format tiles that makes mortar coverage critical has to do with the manufacturing process. During the manufacturing process of most large tiles, the center tends to dome or warp upward. This warpage requires more mortar to be used and air is even less likely to be removed when the mortar is swirled (more on that next).

3. Don't swirl the mortar!

Never, ever swirl mortar! The swirling motion is only for applying resilient flooring adhesive. Yes, you'll get the job done faster, but not with proper mortar coverage.

What happens when mortar is swirled is that air gets trapped with nowhere to go, leaving the tile unsupported. Swirling causes voids where the tile is not bonded to the substrate. That then leads to cracked tile and bond failure under normal use but especially under point load or impact.

4. "Play it Straight!" Comb the mortar in straight lines

The key to successful coverage is “Playing It Straight!” Simply comb the mortar in straight lines. Why? Because trowel ridges running in straight lines are much easier to collapse. They also assist with air removal so you can maximize mortar coverage and ensure a strong bond to the tile and substrate.

  • The first is to “key in” a coat of mortar into the substrate with the flat side of the trowel.
  • Then, add more mortar to the substrate and comb the mortar in straight lines, all going in one direction.
  • With rectangular tile, trowel ridges should go across the short direction of the tile.

Combing the trowel ridges in straight lines provides better distribution of the mortar. This allows better air release when you bed the tile.

Be careful not to leave any voids along chalk lines or between tiles.

5. Backbutter the tile

For large format tile, glass tile, natural stone or any tile set on exterior surfaces, “backbuttering” the tile is recommended.

Use the flat side of the trowel to get an even coat of mortar and fill all the spaces in the surface.

(In addition to floor prep, backbuttering came up repeatedly during the Tuscan Leveling System presentation.)

6. Move the tile in one direction to collapse the mortar ridges

To finish correctly installing tile, set the tile firmly, and move it backward and forward across the trowel ridges about 1/8 to ¼ inch. Move the tile only in one direction, perpendicular to the ridges, without moving in the opposite direction or twisting the tile. Straight trowel ridges collapse with that back and forth motion; that's what eliminates voids.

The video recommends periodically removing a tile and checking for coverage when you first start setting the tile. You are looking for collapsed ridges and no missing mortar. Complete mortar coverage means a much stronger bond.

Note that the larger the trowel, the more back and forth movement is needed.

7. Trowel size matters

Speaking of trowel size, it matters.

You'll want to use a smaller trowel for small tile and a larger one for large tile. Use a trowel that will help you achieve a continuous minimum 3/32” coverage.

Larger tiles most often require deeper notched trowels.

8. Don't ever spot bond tile!

Finally, don't spot bond! Spot bonding with mortar is not recommended for setting tile. (You'll see some spectacular examples of failures related to spot bonding in the video.)

Here's How to Install Tile Correctly and Get Proper Mortar Coverage

Here is the 6:35 minute video titled Trowel and Error which demonstrates how and why to “Play it Straight!” using the NTCA-recommended tile setting method:

What's your reaction to how to install tile correctly? Have you tried to 'Play it Straight' when installing large tiles? What would you add to this list? Let us know in the comments.