*This article by INSTALL executive director David Gross was originally featured in ProInstaller Magazine.
Advances in Self-Leveling Underlayments Change What Installers Need to Know About Surface Prep
Self-leveling underlayment (SLUs) have come a long way in a short time, and the latest innovations are pouring on the pressure for flooring professionals to update their surface prep knowledge. New SLUs offer formula options that can decrease the need for shot blasting and scarifying, are compatible with non-traditional substrates, and include moisture-blocking compounds that impact mitigation layers. And these aren’t the only changes affecting surface prep. Accelerated construction schedules are also challenging installers with tighter deadlines, and the shift to Type 1L concrete has added wider variability to surface prep steps and timelines.
Altogether, the expanding variety of SLU products, the growing number of substrates appropriate for SLUs, changes in construction timelines, and concrete composition have made updated training imperative for professionals who want to remain competitive.
NEW SELF-LEVELING UNDERLAYMENTS RESPOND TO MODERN JOBSITE DEMANDS
Recent innovations in SLU products are changing how flooring contractors approach surface preparation. Driven by faster construction schedules, changing concrete chemistry, and a wider range of installation environments, SLU manufacturers have responded with more specialized and adaptable formulations. Currently, the most impactful SLU advancements are:
Reduced-prep SLUs that minimize mechanical profiling
Some of the latest SLUs are formulated to bond securely with minimal surface profiling, reducing or even eliminating the need for aggressive surface profiling through shot blasting or scarifying. These compounds contain enhanced polymers and additives that promote adhesion to denser, smoother surfaces. For installers, this advancement can mean faster project timelines, less dust and disruption on site, and greater compatibility with evolving slab conditions.
SLUs compatible with non-traditional substrates
Another breakthrough is the development of SLUs engineered for use over substrates beyond traditional concrete, such as metal, rubber, and resilient flooring like VCT. These specialty formulations expand the possibilities for renovation projects, where demolition of legacy materials may not be practical or cost-effective. By offering strong bond performance and dimensional stability across a broader range of base materials, these products allow installers to level and prep complex substrates without compromising long-term performance.
Integrated moisture-blocking SLUs
A growing number of SLUs now incorporate moisture mitigation capabilities directly into the mix. These dual-purpose products are designed to control elevated moisture vapor emission rates (MVER) within specified limits, eliminating the need for a separate mitigation layer in some cases. This is especially valuable in fast-track projects, where slab drying times are compressed and installers may feel pressured to skip mitigation steps, often at great risk. When properly tested and applied, moisture-blocking SLUs can reduce installation time, lower material cost, and limit the risk of moisture-related failure.
These advancements in SLU technology give installers greater flexibility and efficiency on the jobsite, but they require a deeper understanding of product capabilities, substrate conditions, and proper application techniques to ensure long-term performance.
CONCRETE CHANGES ARE ALSO PART OF THE MIX
In addition to self-leveling underlayment advances, the adoption of Type 1L cement has become more widespread. Type 1L contains between 5% and 15% finely ground limestone, and the varying percentage has differing effects. Flooring contractors report greater variability in concrete slab moisture emission rates and surface pH from one jobsite to another, even when conditions seem comparable. Limestone content also influences how primers, adhesives, and SLUs bond to the slab surface and how reliably they cure.
For installers, this means no longer assuming that every slab behaves like those before it. Moisture and pH testing are more critical than ever, and surface preparation techniques must respond to regional differences in slab composition and behavior.
HOW INSTALLATION TECHNIQUES ARE EVOLVING
New self-leveling underlayments offer clear performance advantages, but they also introduce more installation complexity. These products are more sensitive to jobsite conditions (especially when used with Type 1L cement), and they require stricter adherence to manufacturer specifications that vary from one manufacturer to the next. Subsequently, flooring contractors must update their tools and their techniques in several key areas to ensure ongoing success.
Surface preparation
Traditional SLUs typically required aggressive mechanical profiling, such as shot blasting or scarifying, to ensure proper bonding. With reduced-prep SLUs, installers must precisely follow manufacturer guidance to achieve correct adhesion without over-prepping. In many cases, surface cleanliness is more important than roughness. Dust, oil, or curing agents must be thoroughly removed, and substrate conditions must be verified with moisture and pH testing. Elevated moisture or out-of-range pH can interfere with bonding, disrupt curing, or break down adhesives applied later in the flooring system. ASTM-compliant tests, such as in-situ RH probes and surface pH kits, provide the data needed to determine whether the slab is ready for self-leveling and which products are safe to use.
Substrate assessment
When working over alternative substrates such as metal, rubber, or resilient flooring, installers must assess not only the stability of the existing surface but also its compatibility with the SLU being used. Traditional preps often assumed a porous concrete base. Now, installers must factor in expansion behavior, flex characteristics, and bond-break potential. These variables require more upfront evaluation and may demand product-specific primers or transition layers.
Moisture management
Whereas traditional installations might require a separate moisture mitigation system, many newer SLUs incorporate moisture-blocking compounds that change the sequencing and the installer’s role. It is no longer enough to pass the slab off as acceptable once mitigation is applied. The installer must understand the SLU’s moisture limits, ensure substrate conditions are within those parameters, and apply the product in a way that maintains its barrier properties.
Application precision and coordination
Modern SLUs are often formulated for rapid flow and fast curing. While this can save time, it also leaves little room for error once the pour begins. Installers must carefully coordinate crew roles, specific mixing times, proper ratios, and walking paths to maintain a wet edge and prevent cold joints. Tools such as gauge rakes, smoothing tools, and spiked rollers must be used exactly as specified.
A key decision during planning is whether to hand-pour or pump the SLU. Pumping is ideal for large, open areas, while hand-pouring may work best in smaller or restricted spaces. Either method can produce excellent results when the right process is matched to the project scope and site conditions.
When applied correctly, these advanced SLUs produce a smoother, flatter surface that enhances the appearance and performance of finished flooring and reduces the risk of adhesive failure or telegraphing defects.
THE PERFECT POUR: TRAINING & TECHNICAL EXPERTISE
It’s no longer enough to follow the same surface prep routine from job to job. Today’s installers must understand the interactions among material chemistry, site conditions, and sequencing decisions. Surface preparation training programs offered by manufacturers and accredited organizations bridge this knowledge gap and teach both product handling and workflow logic. A quality SLU curriculum includes:
Surface profiling and priming
Understanding when mechanical profiling is necessary, verifying that contaminants are removed, and selecting the right primer for the substrate.
Mixing and application techniques
Following precise ratios and mixing times, maintaining a wet edge, using tools correctly, and coordinating crews to prevent cold joints.
Moisture and pH testing
Performing ASTM-compliant testing and understanding acceptable thresholds and when mitigation is necessary.
Safety and environmental control
Managing dust, PPE, and equipment, especially in finished or occupied spaces.
Surface preparation, especially when self-leveling products are involved, is as much a problem-solving discipline as it is a manual trade. Installers are not just laborers — they are technical experts whose knowledge and judgment determine the final performance of the flooring system. With ongoing education and training, skilled professionals will continue to stand apart in this rapidly evolving industry.