Concrete Floor Leveling in Seattle
Concrete floor leveling makes an interior slab flat enough for new flooring, usually by pouring self-leveling underlayment over it or grinding down its high spots; it doesn't raise a sunken outdoor slab the way slab lifting does. Uneven concrete floors - whether from settling subgrade, original poor workmanship, or slab curl over time - cause flooring installation failures, tripping hazards, and drainage problems. Seattle Concrete specializes in floor leveling for residential basements, garage slabs, commercial warehouses, and interior floors being prepped for LVP, tile, hardwood, or epoxy coatings.
Free on-site estimate · Call (206) 552-9998 or request a quote
Looking to lift a sunken driveway, patio, or sidewalk instead? See slab lifting and leveling.
Leveling methods: self-leveling vs. grinding vs. mudjacking
Self-leveling underlayment (SLU) is poured over the existing slab and flows to find a flat plane. It goes down to 1/8 inch and up to 1.5 inches per lift. Walkable in 4–6 hours, ready for finished flooring in 16–24 hours. Best for floors being brought up to a finished elevation.
Concrete grinding removes high spots - it brings the floor down to the flattest achievable plane. Often combined with SLU: grind the high spots, fill the low spots. Best when the floor needs to come down in specific areas.
Mudjacking / foam lifting raises entire sunken slabs by injecting material underneath. Best for outdoor slabs (driveways, patios, garage aprons) that have settled as a unit. Not typically used for interior finishing prep.
Floor leveling cost in Seattle
| Method | Cost (per sq ft) | Notes |
|---|---|---|
| Self-leveling underlayment | $4–$8 | Includes pour + surface prep |
| Grinding (surface correction) | $1.50–$4 | Per sq ft; more passes = higher cost |
| Mudjacking (exterior slabs) | $3–$8 | Per sq ft of slab raised |
Most interior floor leveling projects complete in 1–2 days. We provide a free on-site estimate after evaluating the slab’s current flatness and identifying the root cause of unevenness.
Preparing a floor for finished flooring
Most interior leveling we do is prep work for a finished floor: luxury vinyl plank (LVP), tile, hardwood, or polished concrete. Each surface has its own flatness tolerance. LVP and laminate are forgiving — variations up to 3/16 inch over 10 feet are acceptable. Tile is stricter: 1/8 inch over 10 feet for large-format tile (anything over 15 inches), and a crack-isolation membrane is recommended on slabs with hairline cracks. Polished concrete demands the tightest tolerance because the finished surface reveals every variation that grinding can’t resolve. We confirm the manufacturer’s flatness specification before quoting the prep so the floor is built to the right standard the first time.
Slab condition assessment
Before recommending a method, we check slab moisture content, existing crack patterns, and the cause of unevenness. Moisture readings — calcium chloride or relative humidity probe — determine whether the slab is dry enough for self-leveling underlayment and whether a vapor mitigation system is needed before the pour. Active cracks (those that move seasonally or under load) have to be addressed before the leveling pour, otherwise the underlayment telegraphs the crack through to the finished floor within months. In Seattle, expansive clay soils and high winter water tables are the two most common drivers of slab movement in residential basements; addressing the subgrade drainage often matters more than the surface leveling itself.
How a self-leveling underlayment pour works
Self-leveling underlayment is a pourable cement-based compound that spreads under its own weight to a flat plane. The quality of the result depends almost entirely on the prep. Old adhesive, paint and loose concrete are ground off so the underlayment can bond. Cracks and joints are filled, and gaps at walls, drains and doorways are dammed so the liquid doesn't run under baseboards or into the next room. The slab gets the primer the manufacturer specifies, which keeps the concrete from drawing water out of the mix too fast and causing pinholes or weak spots. The material is then mixed in batches and pumped or poured in one continuous pass, with gauge rakes and spiked rollers to set thickness and release air. Edges are feathered where the new surface meets existing flooring. Before tile, LVP or glue-down wood goes on, the flooring manufacturer's drying time and moisture limits still apply. Our article on self-leveling underlayment vs. grinding a concrete floor compares the two approaches side by side.
Commercial floor leveling
Commercial work raises the stakes on flatness and schedule. Typical projects are tenant improvements where a new LVT, carpet tile or sheet floor goes over an old slab, retail and office spaces with dips from removed walls or equipment, and warehouse floors with curled joints that rattle forklifts and pallet jacks. Large areas are pumped in continuous placements so there are no cold joints in the underlayment. Work is often phased around occupied space or done after hours, and the moisture testing and flatness readings are recorded for the flooring contractor's warranty requirements. Where a floor only has scattered high spots, concrete grinding alone can be the faster fix. If the slab itself has dropped, that is a lifting or structural problem rather than a leveling one.
Frequently asked questions
What causes uneven concrete floors?
Settling subgrade, water infiltration under the slab, original construction error, or natural slab curl over time. We identify the cause before recommending a fix.
Self-leveling underlayment vs. grinding — which do you recommend?
Underlayment is best for floors that need to be raised to a finished elevation (under LVP, tile, or hardwood). Grinding works when the floor needs to come down to expose a level plane. We often combine both.
How thin can self-leveling concrete go?
Most products go down to about 1/8 inch and up to 1.5 inches in a single pour. Deeper variations are built up in lifts.
How long before we can walk on a leveled floor?
Most self-leveling underlayments are walkable in 4–6 hours and ready for finished flooring in 16–24 hours.
Do you level concrete floors in basements?
Yes — basement slabs are one of our most common leveling jobs in Seattle's older housing stock.
Should I hire a self-leveling concrete contractor or let the flooring installer do it?
Flooring installers often handle small patches. Large pours, floors that are off by more than about half an inch, damp basement slabs, and commercial floors are better handled by a concrete crew that tests moisture, preps the slab, and pumps the underlayment in one continuous pour.
Can self-leveling underlayment go over a damp basement slab?
Not until the moisture is measured. If readings exceed the underlayment or flooring manufacturer's limits, a vapor mitigation coating goes down first, and any water coming in through cracks or the floor-wall joint is fixed before the pour.
Service areas
We handle interior floor leveling across King, Snohomish, Pierce, and Thurston counties, including in Bellevue, Lynnwood, Bothell, and Arlington. See all service areas.
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