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The importance of a flat subfloor 

At LaValle Flooring Inc, we believe that the biggest differences between a failed and successful flooring install is proper prep. Often, it’s the most neglected aspect of the project. There are various things that need to be done before flooring installation can commence, but what we want to touch on today is the importance of a flat subfloor.

Used Uzin 182 low slump patch to level low spots in floor prior to LVP flooring installation.

In the ceramic & stone side of the flooring world, we have a saying “Level is Desired, Flat is Required.” This saying should apply to all other surfaces, such as carpet, sheet vinyl, and click products. An uneven subfloor can lead to premature wear and even complete failure in the form of separation.

“Level is Desired, Flat is Required.”

Checking for a flat sub floor:

Checking for a flatness is crucial but isn’t difficult. The main tool we use to identify high and low spots is a 6 foot concrete screed. The main tool we use to correct high spots is a concrete grinder and a HEPA vacuum. The main tool we use to correct low spots is the same 6 foot concrete screed. There are shorter and longer concrete screeds, we use a 6′ screed for transportation reasons.

Using a concrete screed, we cover the entire floor ensuring there are no areas that exceed the maximum manufacturer specifications for flatness. Products such as Beauflor Pure LVT/ LVP use a 3/16″ per 10 foot radius spec for determining flatness.

Using the screed and a pencil, we mark the radius of the low spots as well as marking the extent of the high spots. Once we’ve covered the entire floor and identified the areas that need addressing, we can commence prep. We use a grinder to lower high spots with a HEPA vacuum to prevent airborne dust. We use patching products such as Uzin NC 888 or NC 182 to fix most low spots. For larger areas, self leveling is another option.


When to patch, when to self level:

Self Leveling at Bridge City Dentistry prior to glue down LVP flooring installation in Valley City, North Dakota.


Often, we’ve heard flooring installers use the terms “patch” and “self leveler” interchangeably. This causes confusion for end users who might think they’re paying for a product and service when they may not be receiving said product. The main difference between self leveling and patching compounds is priming, mixing requirements, and performance characteristics.

On average, bags of self leveler cost less per pound than bags of patch. However, bags of self leveler generally weigh 50lbs while bags of patch weigh 10lbs. A professional floor contractor is best suited to determine if your floor needs self leveling over patching. At LaValle Flooring, we typically will self level floors of 600sqft that have many identified low spots of over 1/8″.

When choosing to self level, it mostly comes down to direct product costs and time. Some rapid setting patches are cover ready in under one hour while most self levelers require a minimum of 12 hours before floor coverings can be installed over the top.

This is due to curing times, self levelers and patch both have much shorter curing times than traditional concrete. For this reason, self leveler/ patch are more expensive than traditional concrete as well. Entry level patching compounds cost $1.40/lb while self levelers cost around $0.56/lb. Determining whether to use self leveler or patch is a calculation that’s unique to every project.

Examples of failures:

A few examples of failing to have a flat subfloor include but are not limited to:

  • Gapping in click products
  • Telegraphing in vinyl products (bumps from debris, grout joints, low spots, etc)
  • Cracking in tile and grout joints
  • Premature wear of high spots
  • Accumulation of dirt and debris

here is an example of a flooring failure due to improper subfloor prep:


In Conclusion:

For the sake of transparency, it is possible to have a successful flooring installation without leveling high/ low spots. Much like it’s possible to survive a car accident without a seat belt. More often than not, the failures outnumber the successful installations, so much so that we strongly encourage proper prep procedures be observed.

By not prepping your floor properly, you are voiding your flooring manufacture’s product warranty as well as increasing the chances of having to replace your floors ahead of time. At LaValle Flooring Inc we know that a properly prepped floor is unlikely to fail which is why we feel confident warrantying our installations for the lifetime of the floor. We hope this has been informative, if you have any questions, the best people to consult are your flooring contractor and product manufacturer.