Lippage and assumptions

I recently had to inspect an installation of porcelain floor plank.
The complaint was “chipping.” Because it was a porcelain product, I was surprised because these products have the reputation for durability and I’d not heard of a case of this type of wear before. The project was a wood-look plank in a “café” area of a senior living facility so that didn’t seem very high traffic to me.
By Christopher Capobianco

I have been selling porcelain tile for the past four years or so, after a 32-year career working mostly with resilient flooring and carpet. I have been slowly learning more about tile from a technical point of view, and really dug in when I had to help diagnose this “chipping” complaint.

I checked in with the importers of the tile and their first thought was that chipping along the edges could be the result of lippage, where one tile is higher than the tile next to it. The high edge can get caught as something is moved across the floor.

Christopher Capobianco

What is lippage? The industry standard definition by ANSI (American National Standards Institute) says: “Lippage refers to differences in elevation between edges of adjacent tile modules.” In other words, a tile is higher than the tile next to it. Lippage can be caused by imperfections in the substrate or variations in the thickness or flatness of the tile itself, such as slight warpage that is inherent in many tile products.

Lighting can also be a factor, as it can be with so many types of floor coverings. If the light hits a floor a certain way, a small amount of lippage that may be within standards may look much worse than it actually is because of shadows. This can occur on floor or wall tile. Like many, I have been guilty of some false assumptions regarding tile installation.

Luckily, some people smarter than I corrected me and nudged me towards industry standards and associations to learn more. The tile industry has done a great job in this area. With the wide variety of tile and stone from all over the world, having written standards is the only way to go “by the book” with consistent product standards and installation procedures.

Wood-look porcelain planks are wildly popular and assumed to be “easy” to install. However, standards and installation procedures are important to follow in order to achieve a flat finished floor.

Then again, from my own experience writing resilient flooring standards, a good standard is one thing but getting people to follow it is another. I have always admired how the tile industry has been so good at disseminating the information contained in these standards.

Even without a strong tile background, I know about TCNA (Tile Council of North America) standards for doing tile “by the book.” As far as those assumptions, with a traditional thick mortar bed (often called “mud” although it’s actually fairly dry), there is enough mortar to allow the installer to compensate for substrate irregularities or tile variation as he or she goes.

Add a little more here, take a little away there, and you can create a fairly flat floor. It is often assumed that “thinset” can be used this way also.

Not so, according to the TCNA where I found this excellent explanation: “Thinset mortar is a blend of cement, very finely graded sand, and a water retention compound that allows the cement to properly hydrate. Tile set by the thinset method is adhered to the substrate with a thin layer of “thinset” cement.

The terms thinset cement, thinset mortar, dryset mortar, and drybond mortar are synonymous. This type of cement is designed to adhere well in a thin layer — typically not greater than 3/16-inch thick. For example, a 3/8-inch notch trowel will produce a 3/16-inch coating after the tiles are pressed in to the cement. While very minor adjustments in height can be made, this method is not appropriate for adjusting the level or flatness of a surface. Rather, the tile will follow the plane of the substrate.”

“Very minor adjustments” is an important point here.

Chipped edge of porcelain floor plank.

There is not a lot of room to adjust when using thinset. High spots in the substrate need to be ground down and low spots filled in with the recommended patching compound. A bad floor may even need to have self-leveling underlayment applied first. Because thinset is generally less costly to use, it had taken over as the installation method for the majority of tile installations today. It’s important to use it properly and not make assumptions about what it can do.

Another factor affecting lippage can be warpage of the tile. With advanced manufacturing techniques, this is not as common anymore, but can still happen. It is hardest to manage with a “running bond” installation (also called ashlar) where the end joints are staggered, like a brick wall. If there is some warpage, the end of the tile may be slightly higher than the middle, or vice versa, so where an end and the middle meet you could have lippage.

Allowing a wider grout joint can help minimize the effect. However, a check of the tile before installation isn’t a bad idea to identify any tiles that may be excessively warped. For any kind of floor covering, laying out a large area “dry” before installation offers the opportunity to examine the material for quality, set up the layout and prepare for the installation before spreading any adhesive.

How much lippage is acceptable?

Terrazzo, Tile & Marble Association of Canada (TTMAC)’s Tile Installation Manual states that grout joints of 6 mm (1/4 in.) or wider will be acceptable for lippage of 1.56 mm (1/16 in.), plus the inherent tile warpage. Smaller grout joints (less than 6 mm wide) will have allowable lippage of 0.78 mm (1/32 in.), plus the inherent tile warpage. ANSI requirements are similar.

Measuring lippage: The tile on the right is approximately 1.5 mm lower than the one on
the left (two credit cards). The higher tile has a chipped corner as a result.

This is where the “credit card test” comes from. A single credit card is about 1/32-inch thick so they are often used for a “spot check” of allowable lippage. In the case of the installation I was inspecting, I measured two credit card thicknesses, and for the manufacturer, that was too much. It did appear that something was catching the edge of the tile and causing chipping in a few areas.

The wider the joint, the easier it is to minimize the effects of lippage. A big challenge is the trend towards thinner grout joints. Many designers want a “seamless” looking floor and some have even asked me about a butt joint on tile installation.

TTMAC does not recommend grout joints less than 1.6 mm (1/16 in.) and neither do other industry-standards organizations. That is a very thin joint, so before promising that can be done, examine the type of tile being installed and have a look at the conditions on site. It may be advisable to recommend a wider joint.

This is a different angle, before I put the credit cards down.

In the case of “running bond” patterns with rectangular tile, joints have to be wider; 3.2 mm (1/8 in. to 4.8 mm (3/16 in.). When the owner or specifier insists on narrow grout joints, they need to be made aware of some of these potential issues; a lot more substrate preparation may be needed.

Minimizing lippage certainly depends on the substrate and the condition of the tile. It can also depend on the tile itself. For a tile with a sharp square edge, lippage is much more of a concern because there is nothing to hide the effect. However, if the edge is rounded or chamfered, the unevenness of the edge can help to hide the effect of slight lippage.

I’ve seen the same thing in the vinyl tile category where a square edge tile or plank is much less forgiving than a beveled edge. Proper substrate preparation should include the type of mortar, site conditions such as lighting, examination of the tile before installation and proper grout joint width.

These are factors that need to be addressed to prevent lippage and create the flat floor or wall that the client expects. The expertise of the installer has a lot to do with all of these factors so the owner or general contractor is advised to use experienced tile contractors that are well versed in these variables.

Want to learn more?

Tile Council of North America (TCNA) 

Terrazzo, Tile and Marble Association of Canada (TTMAC) 

American National Standards Institute (ANSI)

ASTM International 

Christopher Capobianco has been in the floor covering industry since the 1970s in various roles including retail and commercial sales, technical support, consulting, journalism, education and volunteer work. He currently is part of the sales team for Spartan Surfaces in New York City. You can reach him via christopher@SpartanSurfaces.com.

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