Self leveling underlayment, also known as self leveling compound or floor leveler, is used to level out shallow dips and humps in a subfloor, prior to installing a finished floor covering. Because self leveling underlayment is very thin, it can be troweled out to make these small adjustments without adding an additional layer of subflooring.


Today we will discuss what self-leveling underlayment is, how it helps flatten a subfloor, and offer a couple of tips from the pros.

What is Self-Leveling Underlayment Made Of?

There are a few different mixtures of self-leveling underlayments available, but generally they all share the same basic idea. Consisting of very thin cement, polymers, and other ingredients, self leveling underlayment is designed to spread out and find its own level, just as any liquid. Special chemical binders also help the material bond to wood, concrete, and many other subfloor materials. Self-leveling underlayment has a very fine texture, and when mixed as directed forms a slurry that can be poured directly onto the subfloor.

Is Self-Leveling Underlayment Hard to Work With?

In most situations, a typical homeowner can successfully work with this material. For those DIYers with experience mixing mortar or concrete, the project will seem familiar. Self leveling underlayment mixes very similarly to portland cement and uses the same tools to apply it. The material can also be used in layers, so if the floor has undulations greater than ⅛”, more self leveling underlayment can be added. 

**Pro Tip**

Be careful when applying self leveling underlayment in many layers, as self leveling underlayment is quite heavy. Adding too much weight to a wood framed floor system can cause floor support problems.

How Do I Use Self-Leveling Underlayment?

In most instances, the self-leveling underlayment will be used in preparation for tile, hardwood, or other finished floor covering. The professionals will often place a long level or straightedge on the subfloor to determine its flatness. If there are humps in the subfloor greater than ⅛”, many times the best option is to use an appropriate sander to remove them. Next, the level or straightedge is again placed on the subfloor, but this time the target is light appearing under the tool.

Light shining under the straightedge indicates a low spot. The pros will then mark this area with a pencil and apply the underlayment, spreading it out until it can be screeded. Screeding is the process of pulling a straightedge across the surface to remove any underlayment higher than ⅛” and spread it to any low areas. The main goal is to fill in the dips without adding any more underlayment than necessary. Once it has been screeded, the underlayment can be troweled as needed and allowed to cure.

What Kind of Finished Flooring Can I Use Over Self-Leveling Underlayment?

Generally, any finished flooring material can be applied over self-leveling underlayment. Because the material is applied in a very thin consistency, it can be used under carpet, sheet flooring, vinyl, tile, laminates and most other finished floors. Self leveling underlayment can also be applied under vapor barriers, carpet padding, and laminate foam underlayments as well.

**Pro Tip**

If available, use a corded, ½” drill and mixing paddle to mix in the water. Many cordless drills lack the chuck diameter or torque needed to turn a large paddle and may result in damage to the drill.

How Does Self Leveling Underlayment Work?

The material comes in bags similar to portland cement, mortar, and concrete. When mixed with water, self-leveling underlayment reacts chemically, just as cement would and begins to harden. If mixed to the correct consistency, self leveling underlayment will spread out when poured onto a surface and seek its own level, lessening the labor required for a very thin coat. If the material is mixed too densely, it will not flow easily and will usually require additional troweling. 

However, self-leveling underlayment is not just watered down cement. Self leveling underlayment contains additional additives like polymers that allow it to flex slightly without breaking. Additional ingredients are added to improve its bonding to surfaces, and still others to keep the material thin so it will flow. Self leveling underlayment can also improve the bonding characteristics of adhesives, like carpet glue and engineered flooring adhesive.

How Do I Use Self Leveling Underlayment?

Different manufacturers will have slightly different directions, but most will work in a similar way. Before the material can be mixed, the floor should be closely inspected for defects. Although it may seem insignificant, even a small irregularity on a floor surface can be troublesome after the finished floor is installed. The first step should be to scrape the floor to identify any fasteners or adhesives that protrude beyond the surface of the subfloor. After these are found and removed, a straightedge can be laid across the floor in sections to identify any humps or dips.

At this point, using the straight edge mentioned earlier, the next step is to identify the high areas and low areas. After the high spots have been corrected via sanding, the self leveling underlayment is mixed according to the manufacturer’s directions. With most brands, this slurry is often poured directly onto the subfloor and lightly screeded to help the material flow. After the material begins to solidify, a long trowel is often used in broad, arching movements to ensure the material fills in the low areas. After the material has cured, it can itself be sanded if needed to ensure the surface is flat.

Self Leveling Underlayment Saves Time and Money

How can using self leveling underlayment save money? Self leveling underlayment is not inexpensive, but compared to installing an additional layer of subflooring like 5/32” plywood sheets, it can save both money and time. Self leveling underlayment does not require the fasteners, materials, nor tools that an additional subfloor does, nor the effort to install them. In many situations, this makes self leveling underlayment the most cost effective solution for uneven floors. 

Editorial Contributors
Matt Greenfield

Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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