How to Lay Subfloor on an Uneven Floor

Concrete Floors

• 1

  Lay a straight piece of lumber across the floor to find the high and low spots of the concrete subfloor. Make sure the lumber is perfectly straight or you won't get accurate results.

• 2

  Mark high and low spots in the concrete with a carpenter's pencil, so you know where they are.

• 3

  Grind the high spots with a concrete grinder down to make them level. Place the straight lumber back over the spots to make sure they are level. You can rent these at various tool rental outlets. If you can't find one for rent, call a company that specializes in concrete floors or floor removal.

• 4

  Mix the floor patch or leveling compound according to the manufacturer's instructions as brands vary.

• 5

  Move the liquid patch to the front of the low spot with a float trowel. Fill in the low spot.

• 6

  Pour the floor patch into the low spot. Screed the patch with a straight edge. It's best to have two people with one on each end of the straight edge.

• 7

  Clean up any spills as floor patch begins to dry quickly.

• 8

  Install the subfloor over the leveled floor. Depending on the type of floor you are installing, you may not need an additional subfloor, or you may need to make a raised subfloor for hardwood. For a raised subfloor, you'll need to install joists to keep the moisture away from the plywood subfloor. Take precautions with your subfloor to be sure it is the correct type for your finished floor and can be installed over the initial subfloor.

Vinyl or Linoleum Floors

• 9

  Apply embossing leveler to old vinyl or linoleum flooring that has indentations or a rough texture. Embossing leveler is a liquid that you can purchase at flooring centers. Different brands will vary on application, so read the instructions carefully.

• 10

  Lay a carpet pad over the entire uneven floor if you are installing carpet. The carpet pad will cover smaller areas that are uneven. If the floor is significantly uneven to the point of major dips or ridges, rip up the plywood subfloor to start from scratch. Lay a new plywood subfloor. Attach it to the floor joists to prevent tripping and buckling.

• 11

  Lay pieces of flat plywood under the carpet pad over the entire floor for a quick fix of uneven floors. The flat plywood will create a flatter surface for the carpet. This isn't recommended as it doesn't exactly fix the uneven floor. It's simply a quick fix.