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Concrete floor leveling and cementitious underlayments

Floor leveling corrects the high and low spots in a concrete slab so the surface meets the flatness your finished floor requires. Core Floorings Inc installs self-leveling underlayments and cementitious toppings on commercial and industrial projects in Chicagoland and Northwest Indiana, so tile, resilient flooring, carpet and coatings go down on a floor that is ready for them.

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When does a concrete floor need leveling?

A slab needs leveling when its flatness falls short of what the finish flooring or the project specification requires. Flatness is measured with FF (flatness) and FL (levelness) numbers under ASTM E1155, and ACI 117 sets the tolerance classes a slab is expected to meet. Higher FF numbers mean a flatter floor, and a typical commercial office slab may only be specified at a modest number.

One trade article argues that an underlayment can reach a higher degree of flatness at lower cost than building the slab itself to a very high FF. Our team reviews the flatness spec early, so the leveling plan matches what your finish flooring manufacturer actually requires.

  • Visible dips or ponding where water collects
  • High spots that will telegraph through the finished floor
  • A new finish flooring spec flatter than the existing slab
  • Renovation work where new and old slabs sit at different heights

Floor leveling vs a skim coat: which one do you need?

Use a self-leveling underlayment to correct real height differences and a skim coat to smooth minor surface defects. Many projects call for both, with the underlayment first. Our skim coat service covers the thin, finishing layer.

Self-leveling underlayment compared with a skim coat
FactorSelf-leveling underlaymentSkim coat
Best forCorrecting height differences and out-of-tolerance flatnessShallow defects, rough or patched surfaces, minor smoothing
Typical depthRoughly 1/8 inch to 1 inch or more, within each product's limitThin layers
PrimerRequired by nearly every productPer manufacturer data sheet
How it is placedFlows out to find levelTroweled or squeegeed thin

What do we install?

We install cementitious self-leveling underlayments and toppings designed for commercial traffic. Every product has its own minimum and maximum thickness, so we select the material for the depth your slab actually needs and follow the manufacturer's primer and curing requirements. Our main underlayment lines are Maxxon and Ardex, and we use other manufacturers when the project spec calls for them.

Where a slab has high spots, concrete grinding and surface preparation come first. If moisture readings are high, we test and address them before any flooring or underlayment goes down, using our moisture mitigation systems.

How our Floor Leveling process works

  1. 1

    Assess the slab

    We review the flatness spec, check slab condition and moisture, and identify high and low areas.

  2. 2

    Prepare the surface

    Grinding, cleaning and crack or joint repair give the underlayment a sound surface to bond to.

  3. 3

    Prime

    A primer matched to the underlayment helps it bond and perform as designed.

  4. 4

    Place the underlayment

    The material is mixed and placed to the planned depth and flows out to level.

  5. 5

    Cure and verify

    We allow the manufacturer's cure time, then confirm the floor is ready for the next system.

What affects the cost of floor leveling?

Every floor is different, so we price each project from the site, the slab and the spec. These are the factors that move the number. Send us your project for an itemized bid.

  • Total square footage of the area being leveled
  • Depth of fill, since thickness drives material volume
  • Slab condition and the preparation it needs
  • Moisture test results and any mitigation required
  • Site access, phasing and schedule constraints
  • The flatness number the finish flooring requires

Floor Leveling questions

How flat does a concrete floor need to be?

It depends on the finish flooring and the project spec. Flatness is measured with FF and FL numbers under ASTM E1155, and ACI 117 defines tolerance classes. Flooring manufacturers often set their own limits too, so the right target is whatever your specified finish requires. We review the spec early and level to that number.

What is the difference between floor leveling and a skim coat?

A self-leveling underlayment corrects real height differences, generally from about 1/8 inch to an inch or more. A skim coat is a thin layer that smooths minor surface defects. If your slab is out of tolerance, you need an underlayment. If it is only rough or patched, a skim coat is usually enough.

How thick can self-leveling underlayment be?

Every product has its own thickness range, so the limit comes from the manufacturer's data sheet. As a general guide, underlayments correct height differences from about 1/8 inch to an inch or more. For deeper low areas, we choose a product rated for that depth rather than stretching a thin-set material.

Does concrete need primer before leveling?

Almost always. Manufacturers require a primer for nearly every self-leveling underlayment so it bonds to the slab and performs as designed. We follow the data sheet for the specific product, including primer type, mixing and curing, on every project.

Does slab moisture matter before leveling?

Yes. High moisture vapor from the slab can cause adhesives and coatings above it to fail. Testing the slab before work starts tells you whether moisture mitigation is needed first. It is far cheaper to find out before the underlayment and finished floor are installed.

How long before flooring can go over leveled concrete?

That depends on the product, the depth of the fill and the type of finish flooring. The manufacturer's data sheet sets when moisture-sensitive flooring can be installed. We give you a cure and sequencing schedule in the bid so your other trades can plan around it.

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Have a floor that needs to perform?

Send us your drawings, square footage and schedule. We will walk the site, test the slab and get you a clear, itemized bid.

Request a BidIllinois (312) 525-8827Indiana (219) 533-2662

What to send us

Have these ready and we can turn your bid around faster.

  • Drawings, specs or a floor plan
  • Approximate square footage
  • Current floor condition (photos help)
  • Your target schedule

Email plans to sales@corefloorings.com