Reactive adhesives

Heavy-duty applications demand special care

 By Christopher Capobianco

Even with the advances in adhesives, there are still applications that call for two-part epoxy or polyurethane. Known as reactive adhesives because the two parts cure by chemical reaction when mixed, they’re different from standard adhesives that dry when water or solvent evaporates.

I won’t get too much further into the chemistry, but the great holding power of reactive adhesives has been proven over and over again for a variety of products besides flooring. The fact is, in a high traffic area, reactive adhesives will hold the floor in place firmly while resisting temperature extremes, and prevent water on top of the floor as well as indentation from standing and rolling loads. Reactive adhesives do this better than most other adhesive systems.

Christopher Capobianco
Christopher Capobianco

These reactive adhesives are waterproof, but their resistance to water is often misunderstood. Floors in bathrooms, kitchens, entrance areas, and other floors subjected to moisture will perform very well with a reactive adhesive. However, moisture from below is another story, so don’t make the mistake of assuming that concrete moisture problems can be solved using these adhesives.

For installers, there are some key things to know when working with reactive adhesives. First, temperature. If the adhesives are cold, they will take a lot longer to set up and vice versa if they are hot. Ideal job conditions are around 20 degrees Celsius, plus or minus five degrees, for all adhesives and flooring.

Of course, job sites are not always ideal. With reactive adhesives you have the ability to do something about it. In warm weather, keeping adhesives in a cool place, even a cooler, prevents them from setting up as fast. And, if you get a bubble soon after setting the flooring into adhesive, a little heat and a roller can speed things along and help the floor lay flat. On the other hand, in cold temperatures, reactive adhesives can take forever to set up, so don’t start if there is no heat in the space, and keep the adhesives from being too cold.

As far as substrate testing and preparation, the same rules apply as they would for any other adhesive application. The floor needs to be dry, smooth and flat. The trowel notch size is important, too, so make sure you have the right trowel before you get started. It’s usually a very fine notch trowel. You don’t need a lot to do the job and too much can absolutely ruin the installation. Don’t forget this detail!

Everything must be ready before you open the cans and start mixing. Once you mix, you need to use the mixture right away. Do not mix partial units, because the mix is not always a 50/50 measure of the two parts. Always mix a full batch. Use smaller units for jobs where you are not able to do large areas in a single shot. Check instructions to know which part goes into which, such as “pour part A into part B.”

Get all of part A out of the container and mix thoroughly but slowly with part B. I prefer a slow speed electric drill (not much more than 200 RPM) and a metal mixing paddle. If you mix by hand with wooden mixers, you need to mix for at least five to seven minutes — with an electric drill, three to five minutes. The colour of the new mix must be completely uniform with no streaks. After mixing, immediately pour the mix onto the substrate. Don’t mix with a high-speed drill and don’t leave it in the can, because it can generate heat and start to harden quickly if you do.

Start spreading the adhesive immediately using the correct trowel. With sheet goods, spread adhesive in rows going across the width of the roll, which can minimize bubbles. Open time is usually short — around 15 minutes – so make sure you have a watch. Once the open time is up, start setting the flooring right away into the wet adhesive. Reactive adhesives don’t get “tacky,” so don’t expect a strong bond right away. Remember, these adhesives cure by chemical reaction, not by drying. The working time is usually less than an hour, and even less in warm weather. If the adhesive stays open for too long, it will harden and nothing will adhere to it. If this happens, scrape it up off of the substrate and start again.

When laying flooring into wet adhesive, don’t work on top of the flooring. You risk adhesive oozing, shifting flooring, or indentation from your knees. If you have to work on top of the new floor, use kneeling boards such as plywood or foam insulation.

Once the flooring is set, immediately roll in both directions with a 45 kg roller, and again about 30 to 45 minutes later. For sheet flooring, start rolling width-wise in the same direction as the adhesive rows you spread. Lift occasionally to ensure proper adhesive transfer; the back of the flooring should be covered with adhesive after rolling the floor. If not, the adhesive may have been open too long, so it hardened. If there are any curled edges or bubbles after the first rolling, these need to be corrected right away by using small sandbags or other weights to hold the flooring down while the adhesive cures.

Clean up adhesive from the face of the floorcovering while it’s still wet, following label instructions. Once it hardens, it can be difficult — if not impossible — to remove. Once the floor is done, it should not be walked on for 12 hours, or about 48 hours for rolling loads or furniture.

Take your time and remember that cure time and bond strength can be affected by too much adhesive (wrong trowel), improper mixing, cool substrates, warm conditions, improper rolling, contaminated substrates, excessive vapour emissions, or traffic on the floor too soon after installation. If you take your time and pay attention to details, the finished installation will be one that is there for many years of hard use.

 

Christopher Capobianco is a flooring expert currently working in the metropolitan New York market for Ecore Commercial Flooring. Chris’s family lineage in floorcovering goes back for generations. His career includes time as a retailer, architectural sales rep, technical support manager, consultant, instructor, columnist and active volunteer in several organizations.

 

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