High-flow Self-levelling Underlayment Offers Slew of Benefits

By Danick Lalonde

New technology continues to transform the tile installation process, with some products practically installing themselves. Cutting edge high-flow self-levelling underlayment (SLU) is one such product. It is a game-changer for surface preparation. Many current trends in tile require a near-perfect flat substrate to achieve the intended aesthetic and durability of the flooring. High-flow is the next generation of SLUs for delivering the smooth surfaces needed to meet today’s tile setting challenges.

High-flow SLUs achieve time and labour savings and a levelling performance that helps make the incremental cost over traditional products well worth it. High-flow levelling usually has longer working time (20 to 30 minutes) and quicker setting time (two to three hours) to be ready for light foot traffic. Most are pourable and pumpable, and these compounds are easy to install successfully, even for those with less experience. Further time-savings are achieved by the fact no sanding or skim coating is required. Altogether, this provides a much shorter window for another tradesperson to inadvertently mar the new surface.

With any project, it is critical for installers to properly prepare for applying a SLU, including removing contaminants from the substrate and determining its makeup. The makeup of the substrate dictates its prep. SLUs must be installed over primer. A non-absorptive substrate may only need one coat of primer, while highly absorptive substrates might require multiple coats. Primer not only acts as a bonding agent between the SLU and substrate, but it also lowers the porosity of the substrate. A lower porosity substrate means water remains in the SLU, which can help extend working time. Consult the primer label for the proper application/dilution methods per ASTM F3191.

Today’s wild climate and humidity swings elevate the importance of properly handling high-flow SLUs, their temperature requirements and water demand. Carefully follow instructions for how to store, prep for and mix the SLU. Extreme high or low temperatures can change the prep, flowability and work/set times. For example, high temperatures can cure the SLU too quickly and cause cracking. Make sure to prepare and apply high-flow SLU within the manufacturer’s recommended ambient and substrate temperature ranges. Utilize the mixing water’s temperature to help counteract extremes in air temperature. Humidity levels can also impact work and set times. High humidity can slow the set time, so be certain the SLU surface has cured before allowing foot traffic. Always mix the SLU to the water demand specified. Most high-flow SLUs require a single specific water addition amount and do not allow a water range. Too much water reduces the SLU strength and can lead to cracks and debonding. When pumping high-flow SLU, prevent overwatering by supplying the correct water ratio. Be sure to understand the pumping equipment manufacturer’s recommendations (in addition to the SLU directions, of course).

Another challenge for installers is the added complexity of installing large-format tiles and gauged porcelain tiles and panels (GPT/P). Large-format tiles and GPT/P are extremely unforgiving of uneven substrates. With smaller tile, the standard for floor variation is one-quarter inch in 10-feet. With large-format tiles and GPT/P that standard for variation is cut in half to one-eighth of an inch in 10-feet. New high-flow SLUs help installers meet or exceed these standards. They can easily level from one-sixteenth of an inch up to one-and-a-half inches in one application. These SLUs pour easily and flow to cover even hard to reach areas for consistent, even results across the substrate.

Owners/clients are demanding more from their flooring contractors — fast timelines, uncompromising quality, fair pricing and transparency. High-flow SLUs are helping to revolutionize how contractors meet these challenges. They offer advanced technology that delivers ease of application, quick flow and cure, and smooth, level surfaces.

Danick Lalonde joined the H.B. Fuller team in 2022, as area technical manager for the Canadian region. Danick has worked for multiple tool manufacturers throughout his career, overseeing sales, product training and technical support. He has a special passion for elevating the industry and is constantly searching for ways to improve both hands-on and technical presentations to help installers find better ways to work with the products they use every day and meet performance standards.

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