Sticky Business

If you are in the floor-covering business as a manufacturer, retailer, dealer, contractor or installer, you’ve probably heard about the many benefits of luxury vinyl tile (LVT). The growth of this flooring category continues to amaze industry analysts, with its continued growth and acceptance in virtually all types of applications for commercial and residential construction. One of the biggest drivers in this growth is undoubtably the many visual options available, coupled with the modular nature of the flooring material. Many of us will remember moving around huge rolls of broadloom carpet on a forklift or moving heavy rolls of resilient flooring on a dolly, but with LVT it all comes nicely boxed on a pallet, easy to receive and move in the building. Once the LVT has been dispersed on the jobsite, it becomes a relatively simple, “click the LEGOs together” type of installation process, which is a lot easier than installing broadloom carpet that’s 12 feet (3.66 m) wide or resilient flooring that’s 6 to 14 feet (1.83 to 4.27 m) wide.

A lot of this excitement that LVT provides is based on the unsung hero, the pressure-sensitive adhesive (PSA) used to bond LVT to the substrate. Over the years, many LVT adhesives have been introduced, and manufacturers of these products are inventing new, improved versions almost monthly. With all these manufacturers, brands, products and types available to install LVT, the challenge contractors/installers have is to choose the right one for any given installation condition.

In the beginning (and I will go way back in time here), luxury vinyl tiles or vinyl enhanced tiles were installed with wet-lay, hard-set acrylic adhesives, which required a porous substrate that was very dry. Porous and dry were necessary attributes because wet adhesive was being trapped under an impervious material (LVT) and, for the adhesive to dry, it needed a dry and absorptive substrate. These installations went well but often required moisture mitigation, self-leveling installation, and a lot of time for installing flooring into wet adhesive.

NOTE: It is very important to note that adhesives designed for the installation of LVT must be plasticizer-migration-resistant, which means that formulations based on styrene-butadiene rubber (SBR) and hydrocarbon resin blends (typically used for VCT and broadloom carpet) cannot be used. LVT is plasticized, either using phthalates or other chemicals to make the tiles flexible and installable. SBR adhesive bases do not stand up to plasticizers and therefore acrylic adhesives, which are plasticizer-resistant, are the best solution. There are some other adhesive types available for LVT other than acrylic, which we will discuss later in this article. The most important thing to remember is that whatever adhesive you use for LVT must be plasticizer-resistant.

Returning to the installations: Using wet-lay adhesives on dry concrete substrates became a huge issue for the fast-paced, high-pressure, get-it-done-now world of floor-covering installation. Installing into wet adhesive with limited working time was one thing. Getting a dry subfloor was completely another. Enter the hero of the story, in the form of an acrylic pressure-sensitive adhesive.

Adhesive manufacturers began creating pressure-sensitive adhesives at higher moisture limits for concrete subfloors, thereby allowing contractors to install on newer slabs a lot faster without the need for moisture mitigation and leveling. The trend started out at 8 lbs. (3.63 kg) in MVER per ASTM F1869 and 85% to 90% in relative humidity per ASTM F2170 and now, bringing this story up to current events, virtually everyone has a pressure-sensitive adhesive for LVT with a moisture limit of 99% in RH and commonly up to 15 lbs. (6.80 kg) in MVER. This provides a huge benefit to the contractor – in savings thanks to not having to moisture-mitigate and in labor thanks to be able to spread huge areas with adhesive, allowing them to flash until the adhesive no longer transferred to the touch, and then installing flooring to their heart’s delight. Even working times extended up to six hours or more. Everything was good with the world. Or at least so we thought...

The one thing everyone seems to forget or at least overlook is that LVT is a piece of plastic and, as such, is sensitive to temperature just like any other material. For example, if you install LVT on a 90°F (32°C) day in an unacclimated environment, it could look great when you leave but a week later, after the building owner moves in, you could very likely get a call from the building owner saying that there are gaps all over the floor. You could say, “That’s not possible! It was perfect when I left!” But what happened is simple science. The LVT was installed warm, making it slightly larger than it would be at room temperature. The building owner took possession of the property, turned on the HVAC and brought everything down to 72°F (22°C). Not only did the air cool but so did the flooring. When the LVT cooled, it shrank back to its room-temperature dimensions and left gaps at every butt seam across the floor.

It is important to note that LVT will change dimensions with changes in temperature. It is also important to note that pressure-sensitive adhesives will move under that pressure. The pressure in the above example came from the shrinking LVT. Because the PSA is not rigid, it will flow, allowing for gapping to occur. The fault here is clear in that LVT must be acclimated and installed in the working temperature of the room to minimize any gapping.

The opposite of gapping can also occur. This is called “peaking,” and it happens when LVT is installed at room temperature and then exposed to high heat such as radiant heat systems or UV radiation from large windows. These elements will warm up the LVT, causing it to expand as well as soften most PSAs. When the LVT grows, it smashes up against the next piece, causing peaking.

What we are now seeing from the flooring manufacturers/importers of LVT is that they are no longer supporting pressure-sensitive-type adhesives and installation methods, forcing installers to return to using a wet-lay or semi-wet-lay technique. This change in direction is a direct result of the industry trying to control the main complaint about LVT – gapping (or peaking). There is some advantage in using a pressure-sensitive adhesive in a wet-lay installation method. The main advantage is greater bond and therefore increased shear, which does a little to reduce the potential for LVT gapping/peaking. Pressure-sensitive adhesives are pliable – that is how they work. The greater the pressure, the more they press into the flooring material. Even those that are “transitional” or “phase changing” will all exhibit some movement under shear – there is just no way around it. The main disadvantage to the contractor with these new directions is that his installation efficiency just went out the window and he must go back to a wet-lay installation method.

The bottom line is, pressure-sensitive adhesives are great at what they do if you can control the temperature of the flooring material and/or the room in which it will be installed, and if you can prevent any major swings in ambient temperature that could cause gapping or peaking. When you can’t control those factors, then you need to look at other adhesive alternatives. Going back to the old way of using a hard-set, wet-lay acrylic is one way to do it. Using a reactive adhesive, whether it be a two-part epoxy or a moisture-curing modified silane, will also do a lot to control gapping and peaking. These types of adhesives are highly recommended if you are installing LVT in front of a plate-glass window with lots of sunlight streaming in. The UV radiation coming through the window will heat that LVT up 20°F to 30°F (11.5°C to 17°C) over ambient room temperatures, so you really need to make sure that the LVT is extremely well bonded. When in doubt, always reach out to your manufacturer of flooring or adhesive for the best recommendation on your next LVT installation.