Mar. 24, 2025
Self leveling compound, also known as self leveling underlayment or self leveling concrete, is a flowable material used to create a smooth, flat surface prior to installing floor coverings like tile, vinyl, or wood. As the name suggests, self leveling compounds level themselves out to create an even surface without the need for tools or manual labor to spread and smooth.
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While self leveling compounds provide a convenient way to create a flat, smooth subfloor, using a primer underneath provides additional benefits. Some key reasons to use a primer include:
Primers enhance the adhesive bond between the self leveling underlayment and the substrate underneath. This prevents shifting, crumbling edges, cracks, and other bond related issues.
Primers create a protective barrier to reduce moisture transfer between the substrate and self leveling mix. This prevents moisture issues like bumps, craters, and de-bonding.
Variations in substrate porosity can lead to an uneven cure and moisture pockets. Primers help standardize absorption rates for consistent drying.
With an understanding of why priming is important prior to pouring self leveling underlayments, now let's discuss how to choose the right primer:
Primers must be compatible with the substrate they are applied to. Most self leveling floor primers are formulated for concrete floors, but specialty primers exist for wood, OSB, and metal substrates.
Common resin types include acrylic, epoxy, and urethane. Acrylics provide basic sealing and adhesion, epoxies offer superior bonding and moisture protection, while urethanes provide the best durability and chemical resistance.
Based on the criteria above, here are reviews of 5 top rated primers for use beneath self leveling underlayments:
Best moisture barrier protection
Mapei Planicrete UA is a 2 component, high solids epoxy primer for porous and non-porous substrates. It creates a thick film to prevent moisture issues beneath self leveling underlayments.
Key Features:
Best budget option
KILZ Adhesion is a fast-drying, water acrylic-latex primer and sealer. It improves adhesion on multiple surfaces at a very affordable price point.
Key Features:
Best high flow primer
Super Flo-Coat is a thin epoxy acrylic primer with exceptional penetration and sealing properties. It has very low viscosity to penetrate deep into porous concrete.
Key Features:
Best styrene-acrylic primer
This water styrene-acrylic copolymer primer consolidates porous or dusting concrete for better adhesion. It has very low odor.
Key Features:
Best low odor oil based option
This alkyd-resin sealer penetrates with superlow odor compared to typical oil based primers. It provides excellent adhesion to multiple surfaces.
Key Features:
Once you have selected an appropriate primer for your substrate and conditions, proper application is key:
The substrate must be cleaned of all loose particles, dirt, grease, and other bond breakers. Cracks and divots wider than 1/8' should be prefilled.
For 2-component epoxy primers, properly mix resin and hardener as directed. Pre-blended primers just need minor stirring.
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Use a short nap or smooth roller, following spread rate guidelines. Allow primer to fully dry prior to pouring self leveler.
For very porous substrates, a second coat may be required to achieve proper penetration and sealing. This prevents substrate suction from starving the leveler mix.
Using the right self leveling primer for your specific substrate and conditions is important to prevent flooring failures like poor adhesion, moisture issues, and uneven drying. Be sure to evaluate epoxy content, resin type, penetrating abilities and moisture protection to find the best primer for your project. With sound preparation, you can achieve excellent bonds and effective moisture barriers.
It's not recommended as it risks poor adhesion, moisture issues under flooring, and variable cure times. Use a properly formulated primer.
Standard primers require a temperature range of 50-90°F during application and drying for proper film formation.
Allow acrylic and urethane primers to dry 1-2 hours before application. Epoxy primers require 6-24 hours before pouring self leveler.
It depends on the type selected. Check manufacturers guidelines, as some can be applied to damp concrete up to 100% RH.
If the first coat fully penetrates without leaving a film, the substrate is too porous. Re-prime to build an adhesive film layer.
'Self-leveling underlayment' (SLU) is a bit of a misnomer. Although this type of product is incredibly useful, it does require a thoughtful installer to ensure the best results. Follow these guidelines to prevent issues in your self-leveling underlayment installation.
Select a product appropriate for the installation: Know your installation environment and familiarize yourself with the relevant ASTM standards for strength. A commercial floor subject to heavy rolling loads will require a higher-grade self-leveling underlayment (like TEC® Level Set 300 Self-Leveling Underlayment) than a floor in a single-family home.
Also, it is critical to understand your project timeline and choose a product that fits within the appropriate schedule. Some products may require 24-48 hours prior to installing floor coverings while other more premium products are ready to accept moisture-sensitive floor covering in 12 to 16 hours.
Consult product data sheets for information on tensile strength, compressive strength and flexural strength, as well as recommended cure times.
Generally speaking, there are two types of self-leveling underlayments ' traditional and next generation technologies. The most noticeable difference between traditional and next generation SLUs are the flowability and the smooth surface profile of each product. Check out TEC's new high-flow SLU: Level Set 500 HF and for best practice tips for successful high flow SLU installations view our Technical Bulletin.
Some installers prefer the attributes of traditional SLUs because of the working properties. Others prefer the new technology for its high flow properties and extended working time.
The job scope will dictate which product technology should be used for installation. Traditional SLUs work best for deep fill applications greater than 3/16'. The newer technologies are ideal for thinner applications.
Know your substrate: Most SLUs require that all surfaces are fully stable and structurally sound prior to the application of a self-leveling underlayment. For example, understanding your existing substrate porosity is critical to choosing the proper primer. (A simple water droplet test will determine the surface porosity per ASTM F). Equally important is to know the make-up of the existing substrate. For example: typically, sound concrete requires a single coat of primer. Unsealed Gypcrete may require additional steps, including multiple coats of primer prior to the application of cement-based self-leveling underlayment.
Prepare your substrate: Make sure to plug all floor openings, gaps and cracks and install termination dams to prevent any seepage. Consult with product manufacturers to determine moisture limitations of the floor covering, self-leveler, and adhesives to determine if moisture mitigation is needed.
If moisture mitigation is required, this must be done prior to installation of the self-leveling underlayment.
Self-leveling underlayments require the use of a primer prior to installation (like the TEC Multipurpose Primer). Failure to use product recommended primer may result in installation failure. Primer retains the moisture within the self-leveling underlayment to allow proper curing. Secondarily, it acts as a bonding agent to ensure the SLU bonds properly to the substrate. Refer to the primer label for information regarding application methods and dilution per ASTM F.
Beyond priming, most self-leveling underlayments require that the substrate is free from any contaminants that may inhibit bond, including adhesive residue, sealers/curing compounds, oil, grease, loose or peeling paint, or other contaminants. Polished underlayments will require epoxy primers and/or a specific Concrete Surface Profile (CSP), and in these cases, mechanical abrasion (shot-blasting), is required.
Proper water demand: Mix your self-leveling underlayment within the water range specified on the bag. Overwatering will lower the strength of the underlayment and may cause cracking and disbonding. Additionally, a white film may form on the surface of the cured underlayment if the product is overwatered. Failure to properly mix the SLU may make it difficult to work with and lead to improper flow, cracking, or an irregular surface. Mix a minimum of two bags at a time when barrel mixing to ensure optimum efficiencies during the application process. In addition, some SLUs can be pumped. If pumping, special attention is needed to maintain proper water ratios and prevent overwatering. Follow equipment and product manufacturer's recommendations when pumping self-leveler.
Product and ambient temperature: Make sure that the temperature of the room is within the manufacturer's acceptable range. A climate that is too cold or too hot can affect the product, such as increased set time in cool temperatures or reduction in heal time in hot environments. Temperature and humidity will affect flow, working time and set time of the SLU.
Additionally, the temperature of the powder and the water is crucial. Leaving product in the sun, or in a hot environment may lead to flash setting. In situations where warm product is unavoidable, mixing with cold water may help combat installation issues. To maintain cold water temperatures in hot conditions, use blocked or bagged ice in your water barrel.
Whether the environment is warm or cool, acclimating the product prior to mixing is always a best practice.
Use as recommended: Manufacturers will specify the maximum thickness of their product. Some products allow for the addition of aggregate (pea gravel) to increase the depth of the pour, while others only allow their product to be used neat. Be sure to use the appropriate aggregate size and amount when extending a self-leveling underlayment in a single pour. Two separate pours or multiple lifts will achieve the target thickness without the use of additional aggregate. Once the SLU from the first pour becomes a walkable surface, you may proceed to apply the proper primer coat for the additional pour or lift. If a surface is extremely uneven in isolated areas with depressions greater than ½' deep (bird bath), you may treat these areas independent to the final pour. This will assist with the application process by using a consistent amount of self-leveling underlayment throughout the application. Always consult with manufacturers to determine the most suitable product for your application.
Protect your freshly poured underlayment: All self-leveling underlayments should be protected from direct air movement (drafts) during the initial curing process (2-6 hours) as they may cure prematurely which leads to cracking. Generally, most underlayments are not considered final wear layer surfaces. During the final curing process (2-24 hours) they should be protected from excessive construction. Traffic without protection can lead to gouging and irregular surfaces. Allow to cure completely to prevent any unnecessary surface damage, prior to the floor covering installation.
A common theme connects these successful self-leveling underlayment application guidelines: noting and adhering to the manufacturer's instructions. You must read labels and product data sheets carefully to ensure products perform as desired.
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