Home Archive FMTLC for Successful LFT/LHT Installations
Home Archive FMTLC for Successful LFT/LHT Installations

FMTLC for Successful LFT/LHT Installations

By Will White, Director of Technical Communications and Training, Custom Building Products

Apply some FMTLC (Floor Madness Tender Loving Care)
for Successful LFT/LHT Installations

Installing large tiles can be a challenge, especially thick and heavy tiles, typically referred to as LFT (Large Format Tile) and LHT (Large and Heavy Tile). A ceramic or stone tile with any one side 15″or longer falls into this category, which is over 80% of all tile that is sold and installed in today’s market.


Planning is key! Taking the time to evaluate the jobsite conditions and the flatness of the substrate before “turning” the engine on and beginning will make the difference between a painful installation and a smooth one. First, make sure that the wall, floor or other surface flatness is within industry tolerances. Remember the old saying: every job is 75% preparation and 25% installation.

As tiles get larger, inherent warpage or cupping is more likely to be present within tile bodies. This is understood in the tile manufacturing sector and allowances are contained within the ANSI standard for tile. ANSI A137.1 has allowable variation tolerances for different types of tile including porcelain.

This should not mean that the installer has to fix something that’s not right for free or that he/she should pay for the necessary additional surface preparation costs out of their own pocket. Industry standards and guidelines spell out what a floor/wall or other substrate should be in order to set tile; if it does not meet theses requirements, then it needs to be repaired before installation. This should be discussed with the owner or general contractor immediately after assessment of the site conditions and on larger projects it should be put into writing. The American National Institute (ANSI) and the Tile Council of North America (TCNA) both have clear definitions of what those tolerances should be when provided by other trades to the tile contractor.

Concrete shrinks by its very nature.  Most framing contractors don’t have the same flatness tolerances as the flooring industry and gypsum doesn’t always lay flat, so common everyday approaches of grinding, patching or self-leveling may be the best answers to gain proper flatness.

Flatness requirements aren’t just for tile; flatness allowances and tolerances cover all floor finish materials including wood, LVT/LVP, carpet, etc.


Choosing the right mortar is very important.  Not only must it meet bond performance needs, but in some applications, the mortar must be able to experience freeze-thaw cycling, thermal expansion cycling and sustained water immersion. Now add the need to resist slump and sag with large and heavy tile–how confusing can it get?

If surface preparation or flatness is overlooked, then the contractor and his/her installation crew will be forced to make elevation or surface flatness accommodations as they install the tile. This happens all too often in our industry and is not a recommended practice by any organization.

Thin-set mortars are designed as adhesives and should only be used as a bond coat from 3/32″ up to a maximum of a ¼” thick after the tile has been set or bedded, which is clearly listed in ANSI A108 and within the TCNA Handbook.

Using the same thin-set we use every day on all tile types and sizes is probably one of the most common mistakes made in the field every day. When a thin-set mortar is applied too thick (beyond the ¼” maximum), the result can be slumping of the tile and can lead to excessive shrinkage in the thin-set. Now the slump can be evident or obvious when it results in edge between two tiles or two tile courses. However, the shrinkage is probably the silent killer of many tile installations when used beyond its intended capacity. It is silent because shrinkage cannot be seen from the surface and shrinkage can be ongoing well after the tile installation has been completed and even turned over to the owner and or occupants.

That’s why the industry has created new mortar technologies designed to apply thicker for tiles that may have some inherent warpage, cupping, are large and heavy tiles, imprinted backings or ungauged dimensional natural stone tiles. These mortars are easy to identify by looking for the ANSI “H” (heavy) designation on the packaging and on the technical data sheet. H means the mortar is designed to resist slump and shrinkage when large and/or heavy tiles are installed. An LFT/LHT mortar will allow installations from 3/32″ up to ½” thick after the tile has been set or bedded, which also helps to prevent lippage.

But these mortars are not intended to fix or repair deficient flatness tolerances of the substrate. When you do the correct amount of surface prep and achieve proper flatness, your installation will go much, much faster and you won’t experience those challenges of having to build in certain locations and not in others and won’t have the worries of slump, lippage and then that silent creeper, shrinkage.


Older square notch trowel designs have worked well for us for a very long time, but times and tiles have both changed. The square notch pattern requires the setter to set and shift the tile side to side or back and forth to collapse peaks of mortar and fill valleys where there is little or no mortar. This becomes much more difficult as the tile size gets larger and weight increases. In fact, it can be almost impossible as suction plays a role in resisting movement of bedded LFT/LHT. Newer trowel designs can substantially improve collapse and transfer just by setting the LFT/LHT into the wet mortar.

Using a modern trowel, one that is designed to promote ridge collapse and wet mortar transfer to the substrate and the tile backing can make a huge difference. After all, mortar coverage needs to be up to 95% depending on what is being set and where.  New larger tiles, new mortar technologies, why not a new trowel design?


Don’t give me any lip-page in my tile installation. The TCNA definition from the “Flatness and Lippage” section is: “The condition where one edge of a tile is higher than the adjacent tile, giving the finished surface an uneven appearance.”


For porcelain tile with grout joints of 1/16″ up to >¼”, the acceptable lippage is 1/32″– this joint size is found in the majority of our tile installations. For stone tile, the acceptable industry standard for lippage is also 1/32″.

This is a very tight tolerance indeed, as it is the thickness of most standard credit cards (0.79mm).

There are many different lippage control types and designs on the market from screw caps, wedges and caps & straps. Think what you may but, but lippage controls have a proven track record. These tools will improve production as well as your surface flatness results, especially for the newer tile setters in your crew.

Don’t fight with your next job and “build” while setting, only to find massive amounts of lippage and mortar shrinkage. Following the “FMTLC” recipe will get you to that finish successfully, step by step, without any surprises.


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