Concrete Floor Leveling
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.
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 ⅛ 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.
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.
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