“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.
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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 F3191). 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 F3191.
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.
Make sure to check out our entire line of Surface Preparation products. If you need assistance determining which product is right for your job, contact our Technical Support team here or by calling 1-800-832-9023, Mon-Fri 8 a.m. - 6 p.m. CST.
Laying concrete over large areas may seem easy enough for most DIY-ers, but wet concrete is heavy and difficult to move. Hiring professionals to install concrete floors helps reduce the risk of uneven floors.
However, if you notice that your concrete floors are uneven, you do not need to panic. Uneven concrete floors are fixed or repaired through a process known as floor leveling.
Self-leveling concrete is the best solution for repairing concrete floors. This concrete is excellent for concrete floors that have cracks, are sunken, or are uneven. It is a great way to level unleveled surfaces while giving old concrete floors a fresh look.
What is self-leveling concrete?Self-leveling concrete is a polymer-modified cement used to create high-compressive smooth flat surfaces. It does not require large volumes of water and can work on any non-flexible surface, including wood, ceramic tiles, plywood, and concrete.
There are two types of self-leveling compounds; acrylic and water-based concrete. Acrylic concrete is made by mixing cement powder with liquid acrylic polymer.
The water-based self-leveling concrete uses water instead of the acrylic liquid for mixing. They both come as a bag of powder containing the latex compounds for mixing. The water-based self-leveling concrete type is much easier to use and ideal for beginners.
Self-leveling concrete is poured in liquid form and spread in place using a gauging tool. A single pass of self-leveling concrete is usually 0.25 to 1.5 inches thick. The finished product is smooth and flat, with superior compressive strength to traditional concrete floors.
After application, the concrete can be decorated using overlays or concrete stains and dyes. Self-leveling concrete is relatively popular among architects and property owners because of its many advantages over traditional concrete.
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It is easy, quick to install, and useable before or after construction. It also creates smooth and flat floors on tile, plywood, or concrete floors. Therefore, self-leveling concrete helps reduce instances of damage and repair costs.
When to use self-leveling concreteSelf-leveling concrete is quick and easy to install and is therefore quite DIY-friendly. Use self-leveling concrete to repair slightly uneven floors in your home. Use a spirit level to accurately measure the degree of unevenness, then pour the compound and spread it out.
There are many applications for self-leveling concrete. It is perfect for upcycling settled or cracked floors. You can also use it to smoothen and flatten rough and uneven basement floors.
You can also use it as a standalone finishing material, durable enough to withhold daily wear and tear. This makes it suitable for use in retail stores, warehouse floors, institutional facilities, and industrial locations.
For decoration, add stains, pigmented color dyes, and saw cuts, and for a more polished look, consider mechanical polishing.
When not to use self-leveling concreteDespite its advantages, self-leveling concrete is not always the best option. There are some instances when you should not use self-leveling concrete.
Do not use self-leveling concrete without the help of a trained professional. The compound dries very fast and only allows a ten to twenty-minute window from pouring to spreading before it starts to harden.
Self-leveling concrete is best suited as a standalone or subsurface flooring for interior flooring. However, it is unsuitable for outdoor flooring as it doesn’t hold up very well in harsh conditions.
Polymer-mixed, self-leveling concrete also does not cure very well on non-horizontal surfaces. It will therefore be unsuitable for use on vertical walls. It is also not suitable for use where heavy machinery or harsh chemicals are applied.
It is also advisable to avoid using self-leveling concrete on floors with structural damage. It only fixes the surface, so the problem will reoccur if the underlying floor orientation is in bad shape. Perform structural repairs before applying the leveler to prevent the floor from sinking again.
Self-leveling concrete is also unsuitable for repairs in large areas due to its fast drying time and increased cost. A self-leveling concrete bag is more expensive than a bag of ordinary cement.
Finally, do not use self-leveling concrete unless you can clean it right after application. Concrete is very sticky and can stain surfaces and clothes.
How to use self-leveling concreteIt is vital to ensure there’s no structural damage before installing self-leveling concrete. If the unevenness is due to structural damage, you must get that fixed first.
Next, you need to determine the moisture level of the concrete floor. Moisture is normal in concrete, but a high moisture level puts the leveling compound at risk of gradual degradation. The slab must, therefore, be tested to ensure that the moisture level is within acceptable levels.
This can be done using “the relative humidity test using in situ probes.” Once you know the floor is good enough to work on, you can start the installation process. Start by preparing the floor and filling the cracks, then apply primer, mix the concrete and leave to dry.
Clear the floor by removing the room’s furniture, appliances, and baseboards. Remove everything moveable, so you get a good finish. Once the room is empty, clean the floor and remove dust. For best results, sweep first and then vacuum. The clean surface is ready for priming.
Use a filler and a sealer to fill the larger cracks in the concrete floor. To do this, place the nozzle of the filler bottle in the cracks and squeeze out enough filler to fill the crack. You can also press the filler into the cracks to ensure they are adequately filled.
Ensure you have filled all the cracks before proceeding to the next step to avoid wasting the leveler. Allow the filler and sealer to dry, and then prime the surface.
Once all cracks have been filled, use a soft-bristle push broom to apply and spread the primer. Use downward pressure to spread the primer thoroughly, ensuring you push it into the pores of the concrete. Allow the primer to dry for 3-24 hours.
Pour the leveling compound into a bucket and add some water. Use a mixing paddle to mix it until you have achieved the right consistency. Work fast and mix one bag at a time because the compound dries fast.
Since you only have a 10-20 minute window before the compound begins to harden, you should work with a partner. An extra pair of hands is great because one person can mix the compound while the other installs it.
Once the compound is installed, let it dry according to the instructions on the bad. Self-leveling concrete typically takes 4-24 hours to dry, so you should be able to walk on it after 4 hours. Give it at least 24 hours to dry completely before installing any other flooring.
SummarySelf-leveling concrete is a polymer-modified cement used to create high-compressive smooth flat surfaces. It is an ideal alternative to regular concrete because it is easy to use and fixes uneven floors in just 4-24 hours.
Ideal for DIY projects, self-leveling concrete should only be used when there is no structural damage to the existing concrete floor. It is suitable for use on wood, tiles, and concrete.
Self-leveling concrete is best for relatively small spaces because it is expensive compared to cement covering square footage at a much lower cost. Ultimately, self-leveling concrete offers a quick and easy fix for uneven floors.
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