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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Self Leveling Concrete:
What It Fixes, What
It Costs & Its Limits

Underlayment or topping, how many bags you need, how flat your floor has to be, and why most garages should never be self-leveled.
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  • Square footage and room type
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  • Finish floor or coating planned
  • Cracks, settling or moisture
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$2–$5
Per sq ft for a professionally poured self-leveling floor
HomeGuide, 2026
46–48 sq ft
Covered by one 50 lb bag of a common underlayment at 1/8 in deep
Custom LevelQuik RS data sheet
3/16 in
Typical max variation over 10 ft allowed under rigid-core vinyl plank
MSI and Karndean specs
1/8 in
Max variation in 10 ft under tile with any side over 15 in
ANSI A108.02 via TileLetter

Self leveling concrete is a pourable cement-based mix that flows out and finds its own level, filling low spots and leaving a flat, smooth surface for the floor that goes on top. Most of the products sold as self leveling concrete are really underlayments, and several of their own data sheets say in plain words that they are not a wear surface. That one detail decides whether self-leveler is the right fix for your floor. We coat concrete every day, and we get called when a self-leveler was used where a topping or a coating should have been. This guide explains the difference, compares real product specs, and gives you a bag calculator and a flatness checker.

Quick answer

Use a self-leveling underlayment to flatten an interior slab before tile, vinyl plank, carpet or wood. Prime first, pour between 1/8 in and about 1 1/2 in for most bagged products, and expect to walk on it in 2 to 4 hours and install flooring after about 16. If the self-leveled surface will be the finished floor, or will be coated, use a product rated as a topping, not an underlayment. Do not self-level a garage or any floor that is supposed to slope to a drain or door.

What's in this guide
  1. 1Underlayment vs. topping vs. slab leveling
  2. 2Self-leveling product comparison
  3. 3Floor flatness checker
  4. 4Self-leveling bag calculator
  5. 5How to pour self-leveling concrete
  6. 6Can you coat self-leveling concrete?
  7. 7FAQ
Know what you are buying

Underlayment, topping or slab leveling?

Three very different jobs get called "leveling concrete," and the wrong one wastes money.

Most common

Self-leveling underlayment

Flattens a floor so another covering can go on top. Mapei describes underlayments as interior-only products that must be covered. Ardex goes further on K 15: it "is not to be used as a permanent wear surface, even if coated or sealed."

Finished floor

Self-leveling topping

A harder, abrasion-resistant mix meant to be the walking surface, often stained, polished or sealed. Ardex rates its SD-T topping for foot traffic and moderate rubber-wheeled forklift traffic, interior only, at 6,100 psi.

Different job

Slab lifting

Raising a sunken driveway or walk by pumping slurry or foam underneath. HomeGuide puts mudjacking at $4 to $9 per sq ft and foam lifting at $8 to $25. See our concrete leveling cost guide and foam concrete lifting.

If a slab has sunk or tilted, pouring self-leveler on top just adds weight to a slab that is still moving. Lift it or fix the base first. If the slab is sound but rough, uneven or full of old adhesive, self-leveler is the right family of product. Our concrete resurfacing guide covers the thinner trowel-applied overlays for outdoor slabs, where most self-levelers do not belong.

Data sheet numbers

Self leveling concrete products compared

Three widely used products, straight from their technical data sheets. Click a header to sort. Your local options will differ, but the pattern holds: underlayments flow farther and cost less, toppings are harder and can be left exposed.

ProductTypeNeat thicknessSq ft per bag at 1/4 inWalkable (hrs)28-day strength (psi)Wear surface?
Ardex K 15 (55 lb)UnderlaymentUp to 1 1/2 in (5 in extended)302–35,500No, even if coated or sealed
Custom LevelQuik RS (50 lb)UnderlaymentFeatheredge to 1 1/2 in23–2444,500No
Ardex SD-TTopping1/4 in to 2 in (5 in extended)2526,100Yes, interior, foot and moderate forklift
Sources: Ardex K 15 and SD-T technical data; Custom Building Products LevelQuik RS TDS-108. Strength is compressive strength at 28 days.
Tool 1

Do you even need self leveling concrete?

Lay a straight 10 ft board or level on the floor in several directions and slide a tape or feeler under it at the biggest gap. Enter what you find. The checker compares it with the tolerance for your floor covering and tells you whether to grind, patch or pour.

Flatness checker

Floor flatness vs. your floor covering

Tolerances: rigid-core vinyl 3/16 in in 10 ft (MSI, Karndean); large-format tile 1/8 in in 10 ft (ANSI A108.02); standard tile the customary 1/4 in in 10 ft.

Floor details
—
Verdict
—
Allowed in 10 ft
—
Likely fix

Tool 2

Self leveling concrete bag calculator

Self-leveler is sold by the bag and coverage drops fast as depth goes up. Enter the area and the average depth you need, not the deepest spot. A floor that runs from 0 to 1/2 in averages about 1/4 in. The calculator uses each product's published yield, adds 10% for primer-soaked edges and spills, and checks your depth against the product's limits.

Calculator

Bags, timing and installed cost

Bags = area x depth / (bag yield in sq ft at 1/4 in x 0.25) x 1.10. Installed cost uses HomeGuide's $2 to $5 per sq ft.

0.125 = 1/8 in, 0.25 = 1/4 in
—
Bags
—
Walkable
—
Next layer after
—
Pro installed

Working timeLevelQuik RS lists an 18 minute flow time and Ardex K 15 about 10 minutes at 70°F. Every batch has to be poured into the wet edge of the last one. If the calculator says 20 batches, you need a crew and a pump, not a drill and a bucket.
Installation

How to pour self leveling concrete

Self-leveler is unforgiving because it moves fast and shows every shortcut. This is the sequence our applicators use whenever a floor has to be flattened before a coating or a finish floor goes down. Follow your product's data sheet where it differs.

  1. Fix the slab underneath

    Self-leveler bonds to whatever it sits on and will crack where the slab cracks. Route and fill structural cracks first (our concrete crack repair guide walks through the options), and do not pour over a slab that is still settling.

  2. Get it clean and open

    Remove adhesives, paint, sealers, curing compounds, oil and dust. On most commercial jobs that means shot blasting or grinding, not just sweeping. Bond is only as good as the surface you leave.

  3. Prime

    Every product we compared requires a primer. LevelQuik RS calls for its latex primer on all surfaces, and Ardex lists several primers by substrate. Mapei explains why: primer improves adhesion and reduces pinholes, which form when porous concrete pulls water and air out of the mix.

  4. Dam and seal

    Self-leveler goes wherever it can. Seal cracks, floor drains, wall gaps and doorways with foam strip or caulk, and set dams at the edges of the pour.

  5. Mix to the exact water ratio

    Ardex K 15 takes 7 quarts of water per 55 lb bag; LevelQuik RS takes 5.25 to 5.75 quarts per 50 lb bag. Adding water to make it flow farther weakens the surface and causes dusting and cracking.

  6. Pour in a continuous ribbon

    Pour, spread with a gauge rake set to your depth, and keep a wet edge. Install within the temperature window: Ardex K 15 needs at least 50°F during install and cure, and LevelQuik RS lists 50 to 90°F.

  7. Protect it while it cures

    Keep drafts, direct sun and forced-air heat off the pour. Walk on it after 2 to 4 hours depending on product, and wait for the data sheet time before flooring: 16 hours for most coverings on both underlayments we compared.

Coatings

Can you put a coating on self leveling concrete?

This is the question we get most, usually from someone who poured a box-store underlayment in a basement or shop and now wants epoxy or a flake floor on top. The honest answer depends on what is in the bag.

Underlayment

Do not use it as the base for a coating

Underlayments are built to be covered by flooring, not by a hard resin film. Ardex says K 15 is not a wear surface even if coated or sealed, and LevelQuik RS is "not recommended as a finish or wear surface." A thick epoxy or polyurea can pull the weak top layer right off.

Topping

Coat it, after it is ready

Toppings are designed to be sealed or coated. Ardex SD-T accepts waterborne sealers in about 2 to 3 hours but can need up to 7 days before high-build coatings, so check the coating maker's moisture limits too.

Often better

Skip the leveler entirely

Most garage and shop floors do not need to be flat; they need to be sound. We grind, fill the pits and cracks, and let the coating follow the slab. See our epoxy floor coating guide and polyaspartic floor coating guide.

Decorative

Color a topping instead

A self-leveling topping can be stained or dyed for a seamless decorative floor. Our concrete stain guide explains which colorants work on new cement surfaces.

GaragesThe International Residential Code, section R309.1, requires the vehicle area of a garage floor to be "sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway." Self-leveler erases that slope. Melting snow and spilled fluids then sit on the floor. Leave garage slopes alone and put a coating on the slab as it is; our garage floor coating guide covers how. If the slab is rough and you want no prep at all, garage floor tiles float right over it.
Limits

Where self leveling concrete does not belong

  • Outdoors. Mapei describes underlayments as interior products, and Ardex SD-T is interior only. LevelQuik RS allows exterior use only as an underlayment, away from water immersion and sustained heat above 120°F. Patios, driveways and pool decks need an exterior-rated overlay or coating.
  • Wet or sloped-to-drain floors. Shower areas, wash bays and garages need slope. A flat floor puddles.
  • Slabs that move. Heaving, settling or freshly cracked slabs will crack the leveler too.
  • As a coating substitute. Self-leveler flattens; it does not seal out chemicals, oil or water. If protection is the goal, you want a coating, not a leveler.
  • Very deep fills without the right mix. Past roughly 1 1/2 in neat, the products we compared need aggregate extension, and very deep fills may call for new concrete instead.
Uneven or damaged floor?

Level it, repair it, then protect it.

A certified ArmorThane applicator can tell you whether your slab needs a leveler, a repair mortar or just proper grinding, and then install a coating system that will not peel off a weak surface.

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FAQ

Self leveling concrete questions

How thick can self leveling concrete be poured?

It depends on the product. LevelQuik RS goes from featheredge to 1 1/2 in in one pour. Ardex K 15 goes to 1 1/2 in neat and 5 in with aggregate. Ardex SD-T, a topping, needs at least 1/4 in and goes to 2 in neat. Below the minimum, toppings can crack and lose strength.

How long before you can walk on self leveling concrete?

Usually 2 to 4 hours. Ardex lists 2 to 3 hours for K 15 and about 2 hours for SD-T, and LevelQuik RS is walkable in 4 hours. Flooring goes down later: 4 to 6 hours for tile and about 16 hours for most other coverings on the underlayments we compared.

How much does self leveling concrete cost?

HomeGuide puts professional self-leveling at $2 to $5 per square foot. Material cost depends on depth: one 50 lb bag of LevelQuik RS covers about 46 to 48 sq ft at 1/8 in but only 11.5 to 12 sq ft at 1/2 in. Use the bag calculator above for your floor.

Do you need to prime before self leveling?

Yes. All the products we compared require a primer matched to the substrate. Without it, porous concrete pulls water out of the mix, which causes pinholes and a weak bond.

Can self leveling concrete be used as a finished floor?

Only if it is a topping. Self-leveling toppings like Ardex SD-T are designed as wear surfaces and can be sealed, stained or coated. Underlayments like Ardex K 15 and LevelQuik RS are not wear surfaces and must be covered with a floor covering.

Can I use self leveling concrete outside?

Generally no. Most self-levelers are interior products. A few underlayments allow limited exterior use under another covering, away from standing water. For patios, walks and pool decks, use an exterior resurfacer or a coating made for UV and freeze-thaw.

Should I self-level my garage floor before coating it?

Usually not. Garage floors are supposed to slope toward the door or a drain, and the IRC requires it. Grind the slab, repair cracks and pits, and let the coating follow the existing slope.

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