Floor leveling, flat is not the same as level

What is floor leveling?

Floor leveling is the correction of a subfloor surface so it meets the flatness tolerance the new flooring requires - by grinding down high spots, filling low spots with patch, or pouring a self-levelling compound across a whole area. Flat and level are different things. Almost every flooring warranty specifies flatness. Very few require the floor to be truly level, and chasing level in an older house is usually the wrong goal.

Signs you need floor leveling

• Furniture rocks in one place, or a marble put on the floor rolls in a consistent direction
• You can see or feel a dip or ridge when walking barefoot across a room
• Your flooring installer has said the floor is out of tolerance and quoted an allowance for prep
• A concrete slab has trowel ridges, high spots at a control joint, or residue from removed adhesive
• Click-lock plank already installed is popping apart or clicking underfoot in one area
• Two rooms meet at a doorway with a visible step where the surfaces should align
• Tile is planned, and large-format tile is far less forgiving of an uneven surface than the old floor was

Seeing something not on this list? Browse flooring problems by symptom →

How floor leveling actually works

1. 1

   Mapping the floor with a straightedge and a laser

   A long straightedge moved across the floor finds the flatness deviations that matter to flooring. A laser or water level finds overall slope. The two surveys answer different questions and a good contractor does both.

   Watch forOnly a laser being used. A laser tells you the room slopes; it does not tell you whether there is a dip under where the plank joints will land, which is the thing that fails.

2. 2

   Deciding whether the slope needs correcting at all

   An old house that has settled evenly may be visibly out of level and perfectly fine for flooring. The question is whether the deviation over any given span exceeds the flooring manufacturer's stated tolerance.

   Watch forA quote to level a whole floor to true level when the flooring only requires flatness. It is a much bigger, more expensive job, and the outcome may still leave you with out-of-square door casings and skirting.

3. 3

   Grinding high spots

   On concrete, high spots and adhesive ridges are ground off rather than built around. Grinding down is usually cheaper and thinner than filling everything to the height of the highest point.

   Watch forGrinding done without dust extraction. Concrete grinding dust contains crystalline silica, and dry grinding in an occupied house is a genuine health issue, not a housekeeping one.

4. 4

   Patching localised low spots

   Individual dips are filled with a cementitious patching compound, feathered out at the edges so there is no ridge, and allowed to cure before being checked again with the straightedge.

   Watch forPatch feathered to nothing at the edge without a product rated for feather-edging. The thin edge breaks up under traffic and telegraphs through the new floor.

5. 5

   Priming and pouring self-levelling compound

   For widespread unevenness, the substrate is primed, edges are dammed, and a flowable compound is poured and spread. It finds its own level and cures to a hard, flat surface.

   Watch forPouring without primer, or over a dusty substrate. The bond fails, the whole poured layer becomes a hollow-sounding sheet, and removing it is worse work than pouring it was.

6. 6

   Cure and verification

   The compound cures for a stated period, then the floor is rechecked against the tolerance and moisture-tested if flooring will be glued over it.

   Watch forFlooring installed over a fresh pour the same day. Self-levelling compound carries water, and sealing it under a floor before it has dried creates exactly the moisture problem the flooring warranty asks about.

What does floor leveling cost?

Leveling is usually priced by area and by how much material the correction needs, so a floor needing a skim across one room costs far less than one needing depth throughout. Grinding is often cheaper than filling. It is prep, not a finish - see the Cost Guide.

See the full floor leveling cost guide - by material, size and region →

If the number is the problem, here are the ways people pay for it →