Get Moving

Few topics in the tile industry can garner a collective groan from all interested parties more than movement joints. This likely stems from a fundamental misunderstanding of the forces in play and the possible effects on what seems like a simple, static installation. And honestly, I can understand, to a certain extent.

The flooring industry has grudgingly accepted the reality of allowing for movement in wood flooring installations as wood floors have repeatedly shown their explosive potential over the years. The combination of a living, breathing finished flooring material that expands and contracts due to the ambient conditions is an accepted, if not annoying, fact of life.

But tile? Baked clay or porcelain or a rock somebody cut into a geometric shape? Certainly, we don’t need to worry about tiles? These were never towering timbers that grew from seedlings with water coursing through their veins to yield the fruits of life at the ends of their branches. No, we are talking about dried mud and rocks. I can understand how this may seem like an effort in sensationalism. Industry pundits dreaming up ways to make life more complicated for design professionals and installers alike. Certainly, the industry would never expect ordinary people to try and decipher something as complicated as Wm=(L x ΔT x a)/(S/100) to determine how much movement to allow for in a tile installation?

You have probably guessed where I am going with this. That equation is real and pulled directly out of the Tile Council of North America (TCNA) Handbook. This handbook is often referred to as the “bible” of the tile industry. And just like the actual Bible, it can often be misquoted and misunderstood. The volume of information available can be overwhelming if you don’t know where to look or understand what information applies to your installation. (That is a topic all to itself and likely worthy of its own article.) However, here I am discussing a specific section of the handbook: EJ-171, which discusses movement joints. EJ-171 may sound more like the name of a droid in a “Star Wars” movie, but it is the name of the last method in the TCNA Handbook. All kidding aside, it is a poignant example of the old cliché, “last, but certainly not least.”

Tile installation failures are rarely the result of a single factor. The old tile mantra of “the three G’s... God, grout and gravity” has seen many questionable installs through the expected life of a floor. Occasionally, however, we see the consequences of not properly allowing for movement within the installation. When these failures occur and the verdict is read, EJ-171 is going to be the industry document cited every time.

The first sentence of the entire document drives home the most important point that we are hoping to learn, “Perimeter and field movement joints within a tile installation are essential and required.” Honestly, if you remember nothing else from this article, please remember that statement. If you could also squeeze in one addendum to that thought, remember that you can find it in the back of the TCNA Handbook.

Now that we understand we must allow for movement in the installation, we can begin to dig deeper into how to do that. The first major concept that we need to grasp is that we are allowing for two different categories of movement: Movement of the tile itself, caused by thermal expansion and contraction, and movement that is related to the substrate/s. It is also important to note that while this document does provide general guidelines for locations and frequency of these movement joints, it is ultimately the responsibility of the design professional or engineer to designate the locations for movement joints on project drawings. Unfortunately, this amount of detail in the project drawings is often missing, and it is incumbent on the tile installer to understand and communicate the need for the joints to be provided.

A joint by any other name

When we look at allowing for thermal expansion and contraction in a tile installation, we often hear movement joints referred to as “soft joints.” This is not a particularly technical term, but the most common joint you would think about in a tile installation would be a grout joint. The general expectation for a grout joint is that it will be rigid or “hard” and, if it is not, I usually receive a call wanting to know what is wrong with it. Many of the high-performance grouts that are used today have a compressive strength (or psi) much higher than the concrete on which the tile is installed. While that may serve well for the abrasion resistance of the grout joints, it does not allow for much movement in the tile installation.

A soft joint is a grout joint that is left clear down to the substrate. This is an important distinction, as a typical grout joint would have the adhesive mortar filling in the lower third of the joint. For a soft joint to perform appropriately, it cannot have any restraining materials present. Either a bond-breaking tape is placed at the bottom of the joint or a foam backer rod is forced down into the joint. This allows for the flexible sealant to bond to the two tiles, but not the substrate, essentially creating “islands” of tiles that can move independently.

The first section in the TCNA Handbook following the introduction to EJ-171 is titled “Location and Frequency of Joints.” This is convenient since we have already established the definition and importance of the field movement joints, so the next step is knowing where to put them.

Perimeter joints are defined as “movement joints where tilework abuts restraining surfaces such as perimeter walls, dissimilar floor finishes, curbs, columns, pipes, ceilings and where changes occur in backing materials.” If you have ever noticed cracked or missing grout along the side of a room or hallway (which you see quite often if you have a sickness that requires you stare at every floor of every room you go into), that is an example of the importance of perimeter joints. There should never be grout in that joint because the floor and wall move independently of each other. Rigid materials do not do well with the constant stretching and compressing that come with being sandwiched between two surfaces moving differentially.

Cracked grout in a corner may be an eyesore but is not typically a structural concern. The greater concern is the pressure that is being added throughout the tile installation. When the tile heats up, it expands and, instead of having an open relief space capped with a flexible sealant all along the edges, there is a 5,000-psi block of sand and cement constraining that movement. In many interior tile installations, especially smaller residential jobs, allowing for movement on the perimeter can be adequate.

The frequency of field movement joints is determined by classifying the installation into one of four categories: Interior, exterior, interior exposed to direct sunlight or above-ground concrete slab substrate.

Interior installations require a movement joint every 25 feet (7.62 m) or less in each direction. Exterior installations require a movement joint every 8 to 12 feet (2.44 to 3.66 m) in each direction with the caveat, “More frequent joint placement may be required depending on materials and environmental conditions.” This discrepancy goes back to the term “thermal expansion,” meaning caused by heat or temperature. Because almost all modern, interior spaces are climate-controlled, it can be reasonably assumed that these tile installations will move less because of fewer and milder temperature variations.

Consider a west-facing exterior in a high-elevation environment such as Denver, CO. A sunny day in October could easily reach ambient temperatures of 70°F (21°C), while the tiles could easily heat up to well above 140°F (60°C) during the afternoon. Once the sun drops behind the mountains to the west, the combination of the shade and falling ambient temperatures results in a rapid cooling of the tiles. As the ambient temperature drops down below 40°F (4°C) and the tiles rapidly cool to match that temperature, an incredible +100°F (37°C) delta for the tile temperature has occurred in just a few hours. This is just a typical day in October and does not consider extreme weather changes that can occur. Compare that to an interior installation where the temperature likely ranges between 70°F and 80°F (21°C and 27°C) over the life of the floor.

Interior tilework exposed to direct sunlight or moisture needs a maximum distance of 12 feet (3.66 m) in each direction between field movement joints. This is a similar situation to exterior installations because of the heating of the tiles due to exposure to sunlight. This is often found in lobbies and atriums of commercial buildings and hotels and can present some unique environmental conditions, as well. Vaulted ceilings create thermal layers as cold air sinks and warm air rises. And as the sunlight moves across an atrium, the tiles are heating and cooling along with it. This creates vast disparities in the tile temperatures across a single installation. Interiors can also experience moisture expansion near indoor pools, decks, steam rooms and other high-moisture areas, again requiring movement joints every 8 to 12 feet (2.44 to 3.66 m). Allowing for this differential movement requires something much more like an exterior installation than an interior one.

The final category is above-ground concrete slab substrates, where the maximum distance should also be 12 feet (3.66 m) in each direction.

Before we all go cross-eyed and decide our time would be better spent looking at the pretty pictures on the previous pages, let’s get to the point. If I told you a tile expanded one millimeter with a 100-degree F (55-degree C) increase in temperature, that does not sound too bad, right? Can’t the adhesive/grout hold onto a tile that only moves one tiny millimeter? When framed as a single tile, it does not sound like too daunting of a task. But consider that once the tiles are grouted, the stress of the expansion and contraction is shared amongst all the tiles.

If these tiles are 1 x 1 foot (0.3 x 0.3 m) and cover an area 10 x 10 feet (3 x 3 m), you could have as much as 10 millimeters of movement in each direction. If the area was 25 x 25 feet (7.6 x 7.6 m), that would almost equal 1" (2.5 cm) of movement! These are round numbers, used to make the math a little easier to track, but the concept is hopefully clear. By decreasing the distance between soft joints and making them more numerous, we lessen the stress put on the adhesive bond of the tile to the substrate. If I am walking down the sidewalk next to that building in Denver, I would like to think that the tile installation several feet above my head allows for enough thermal expansion.

This is just a cursory introduction to EJ-171, and there is so much more that can be reviewed and expanded upon. Hopefully, the importance of allowing for movement in a tile installation has been made clear. We never got into concrete joints, such as expansion, control, construction, cold, saw-cut, isolation, contraction and seismic joints. There is a glossary for these terms included in EJ-171 as well as a statement that these should all be continued through the tile installation. Joint width and depth are discussed, and materials used in the joints (such as backup strips and sealants) are described and classified. Thirteen different installation details are provided, showing the different joints and treatments.

Section EJ-171 of the TCNA Handbook is only eight pages long, but it is truly comprehensive in covering the pertinent information and responsibilities for the tile installation. If you do not have a copy of the TCNA Handbook, please get one. When you do, don’t forget to look in the back.