What is a Self-Levelling Compound?
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A levelling compound is a self-levelling liquid used to level out uneven subfloors. It is a fast-drying and easy-to-use product that can be applied over various interior subfloor types, including concrete, tiles, timber and particleboard/plywood. Self-levelling compound is typically used to prepare subfloors for floating floor installation, such as laminate, hybrid, engineered timber, and bamboo flooring or other floor coverings as they require a very flat and even subfloor.
Benefits of levelling compound:
How To Determine Whether My Subfloor Needs Levelling
Hard flooring is great, however, their worst enemy is an uneven subfloor. Unlevel subfloors can cause a myriad of problems including bouncing underfoot, creaking noises, and in severe cases – damage to the floorboards themselves! Subfloor unevenness can be caused by several factors, such as poor construction, settling, or moisture damage. Luckily, modern technology brings self-levelling concrete into the picture. These are designed to level out the subfloor by coating the surface which will set into a new flat and even subfloor.
A subfloor is considered uneven if it has any variations in height greater than 2 – 4 mm over a distance of 2m which isn’t a lot if you think about it. Using a spirit level, you can check whether your subfloor is suitable. We recommend a two-metre-long spirit level as it replicates your typical floorboard length. Check the height of subfloor bumps and dips with a ruler as you slide the spirit level across the subfloor. Be sure to rotate and check from different angles.
As a general rule of thumb, most floating floors like laminate boards, engineered timber flooring and bamboo flooring can tolerate around 4mm variance over 2 metres before you begin feeling bouncing underfoot.
Hybrid flooring on the other hand can only tolerate around 2mm variance over 2 metres before the unlevel sections become noticeable.
Note that tiles with large grout lines will require a skim coat of floor levelling compound even if they are flat and even. This is because the click-lock joins can give and break if they are directly above grout lines, especially wider ones.
Can Levelling Compound Be Used On Surfaces Other Than Concrete Slabs?
Yes, they can be used on almost every surface. The application method varies, depending on whether the subfloor is a concrete slab or wooden base. Properly sealed concrete slabs only require a primer before a self-leveller can be poured over, whereas a wood substrate needs waterproofing and sealing as well.
Self-levelling compound cannot be applied over existing floating floors. We highly recommend removing and disposing of any existing floor coverings in advance.
The following subfloors don’t always require waterproofing (may require sealing):
These wood-based subfloors ALWAYS require waterproofing and sealing. This is a non-exhaustive list:
Exceptions which may not be suitable for levelling:
How To Use Self-Levelling Compound On Uneven Concrete Slab
Note: Self-levelling compound is not the only way to level a subfloor. If you wish to discover more methods, check out our comprehensive guide on how to deal with an uneven subfloor.
The subfloor must be clean, dry, and free of dust and debris before applying a self-levelling compound. Any cracks or holes in the subfloor should be repaired or sealed using a suitable filler. Be sure to remove any nails or residue glue from previous flooring or carpets that may have been present.
Important Note: Wooden subfloors like chipboard, timber or yellow tongue require waterproofing and gap sealing during the priming process. Concrete subfloors only require a primer.
A primer is applied to the subfloor to help the self-levelling compound adhere properly. The primer should be allowed to dry completely before applying the self-levelling compound. Rookies often skip the priming process resulting in the levelling compound cracking after drying.
If you have a wooden subfloor, it is important to seal all gaps/holes with sealant or a membrane and apply a waterproof primer on top. This is because wood absorbs moisture which can cause warping or buckling problems down the line if not prepared properly.
The self-levelling compound is mixed with water (or another suitable solvent) according to manufacturer instructions. It is important to mix the compound thoroughly until it has a very smooth consistency and is free of lumps. This can be done easily with an industrial mixer which looks like an oversized egg beater.
The self-levelling compound is poured onto the subfloor from the farthest corner of the room and worked towards the door. This needs to be done carefully to have even distribution across the surface. The compound should be spread out evenly using a trowel or roller if necessary.
Note that most levelling compounds have a minimum thickness of 3mm to maintain structural integrity. Too thin, and it may crack once dried!
Once the self-levelling compound has been poured, it is important to de-gas it to remove any air bubbles. This can be done using a spiked roller or a de-gassing brush. This will otherwise result in air pockets, which means the new substrate won’t be stable once dry. A little bit of residue bubbles won’t cause harm, however excessive bubbles can be an issue.
The self-levelling compound should dry completely before installing the floating floor. There should be no more than 5.5% moisture content reading before installation. You can easily check the moisture reading by purchasing a moisture meter, calibrating for concrete/brick surfaces. The drying time will vary depending on the thickness of the compound and the ambient temperature. The more airflow and open windows (unless it rains), the quicker the levelling compound will dry.
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Installing waterproof floors like hybrid flooring over uncured levelling compounds can result in mould growth in the underlayment. Laying waterproof hybrid flooring with a plastic moisture barrier will minimise this risk, but won’t be as effective as giving proper drying and curing time. Whilst some companies may be willing to install before the levelling compound is dry, they usually won’t offer a warranty for any moisture-related issues that may occur down the line.
How Much Does Self-Levelling Compound & Subfloor Levelling Cost?
Most flooring companies in Sydney & NSW will sell residential-grade levelling compound anywhere from $35 – $50 per 20kg bag. You can cover around 2 square metres per 20kg bag, varying based on the severity of unevenness and the nature of the job. This averages out to $20 – $25 per square metre for supply only.
The market rate for the full subfloor levelling service is $40 – $90 per square metre in Sydney & NSW as of 2024. Subfloor professionals will charge based on the type of subfloor, how uneven it is, and the total size of the job. Wooden subfloor will cost more because they require surface sealing with waterproof primer in advance.
FloorVenue stocks floor levelling compounds specialised for both residential and commercial use. Whether you’re looking for supply only or a full levelling service, do reach out to us. We highly recommend speaking to one of our friendly flooring experts as every job site and subfloor is different. Choose FloorVenue for a solution tailored to your situation!
Disclaimer:
“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 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.
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