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Top 5 Tips for Success Using Self-Leveling Underlayments

Video Transcript

Top 5 Tips – SLU

Welcome to Custom Technical University and our Top 5 Tips for Success using Self-Leveling Underlayments.  

Flooring format sizes just continue to grow!  Porcelain tiles are now over 5’x10’, wood planks are wider and larger; even luxury vinyl planks are almost 8’ long! With this phenomenal growth in size, the need for a flatter substrate is essential to create a beautiful floor. 

For ceramic tiles over 15” long on any side, the industry standard requires no variation in flatness greater than 1/8” in 10 feet or 1/16” in any 24 inches. With these more stringent requirements, and that fact that large formats make up the vast majority of flooring installations, the use of self-leveling underlayments has become standard on most projects. 

In this episode, we’re going to present our Top 5 tips for achieving a truly flat floor. 


Tip #1: Plan the operation before you start

Plan – clean – prime – then pour. 

Over a sound and stable substrate, preparation may only require scraping contaminates and vacuuming.  For more heavy service applications, shot blasting and other mechanical preparation may be necessary.

Prior to leveling, how will you handle existing cracks in the concrete?  Small, in plane cracks, 1/8” or less, that are non-moving or static, could be filled with an engineered cement based patching compound.

Non-moving joints in concrete such as saw cuts or control joints can also be filled with a patching compound. But, any joints that are designed to move should be carried through the underlayment and through the finished flooring.  Use compressible back up strips and flexible sealant such as 100% silicone.

Larger cracks, or cracks that are dynamic are considered structural cracks and will keep moving. Therefore, they must be evaluated and structurally repaired before proceeding. 

Concrete moisture vapor emissions must also be evaluated. Finished floor coverings and some installation products may have limitations.  If excessive moisture is present, treat the slab with a moisture mitigation product such as Custom TechMVC.

Self-leveling underlayment is considered a flowable mortar so have enough spray foam, duct tape or weather stripping to block openings and prevent it from overflowing and reaching an adjoining room or a floor below.

The Tile Council of North America estimates self-leveling underlayment at 2-3/4 pounds per square foot at ¼” thickness. Has an engineer determined that the substrate can handle the added weight of a leveler? 

If the added weight is a concern, consider CUSTOM LevelLite, which is 40% lighter than standard underlayments.

Each product and each job will be a little different, so always read the product technical data sheet before getting started. And, to determine how much product will be needed, use the material calculator on the CUSTOM website or mobile app.   


Tip #2: Understand what a leveler can and cannot do

What does self-leveling mean?  Leveling products are designed to seek their own level, but in the typical thin applications, won’t complete the placement themselves.  The right tools, such a gauge rake and smoother, must be used to move the product into place and smooth the surface.  Smoothing the surface or using a spiked roller also breaks the surface tension and allows the many compounds to flow effectively. 

Self-leveling technology has advanced to provide high performance products that are stronger than ever before, with many options for different project conditions. For example, LevelQuik RS can be applied from a feather edge up to one and a half inches deep in a single pour. It’s rapid curing so most tile can be installed in just four hours and vinyl flooring the next day. 

To flatten or level a plywood or OSB subfloor, fiber-reinforced LevelQuik Advance eliminates the time, labor and cost of installing wire lath. These CUSTOM SLUs are eligible for up to a lifetime system warranty.

For even more options such as higher compressive strengths, deep pours, wear surfaces and toppings, or treating slabs with high moisture, CUSTOM offers the CustomTech line, the industry’s most advanced flooring preparation technology for all floor coverings.


Tip #3: Always use the recommended primer

Self-leveling underlayment requires a primer - this step is critical to achieving a flat floor. The primer helps the leveler create a strong bond and prevents moisture loss to the substrate which can affect flowing and leveling.

Apply the primer according the coverage rate - not too thin and not too thick - and allow it to dry before leveling. LevelQuik Advanced Acrylic Primer can be used over porous substrates when diluted; and non-porous surfaces at full strength.


Tip #4: Measure the water accurately

Self leveling chemistry is very complex! The product is designed to slightly expand so when it later shrinks, it stays flat and stable.  Using the correct amount of water allows these chemicals to react properly.  A range may be given to account for variables on a project; these include humidity, air, water and substrate temperatures. If conditions are moderate, start at the bottom/middle of the range.

Too little water will prevent proper mixing and flow but too much water is even worse.  Adding too much water will cause the aggregate to sink to the bottom and the lighter organic materials to rise, resulting in a weak, powdery surface that will shrink, crack and have low compressive strength. 

For best results, use a high speed mixer with the proper paddle.  Mix for 2 minutes without moving the paddle up and down out of the mixture, as this can entrain air. 


Tip #5: Always have sufficient labor on the job

These installations have to move quickly because of the fast curing properties of self levelers.  Whether barrel mixing or pumping, you only have limited time to get it right.  Make sure your crew is big enough to properly mix, transfer and pour the product, then spread it into place and finally, smooth the surface.  And, you’ll need to keep up that pace until the pour is complete.

These are fast setting products, so don’t place the mixing station too far away.  For the same reason, always keep a wet edge, pouring fresh product to meet the last batch placed – and no spot pouring if you want a flat floor.  

If you'd like to know more about using self-leveling underlayments, visit our website——or give us a call. And be sure to “like” our video, share it and subscribe for the latest tips on tile installation.

Thanks again for joining us at Custom Technical University. See you at our next edition of CUSTOM's Top 5 Tips!


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