How To Level A Floor

Even in newer homes, plywood subfloors and concrete slabs are rarely flat. High and low spots can affect the look of a finished floor, interfere with the installation, and even lead to material failure, especially in tile floors.

How to Level Different Types of Floors

Most flooring manufacturers recommend a variation of no more than 3/16 inch over a 10-foot span. Floor leveling is a relatively easy DIY project, although some subfloors with rot, insect damage, or structural issues may require professional attention.

How to Level a Concrete Floor

Finding the high and low spots

Start by locating the high and low spots before leveling a subfloor. To do this, you will need a straightedge (at least six feet long) and measuring tape. Use a long straightedge, such as a long spirit level or a straight board held on its edge. Starting at one side of the room, swing the straightedge from one reference point across the floor and mark the high and low areas (any deviations greater than 3/16 inch) with a pencil. (You can also use a string line stretched between two points or a laser level to measure the variations in the floor’s surface.) Continue around the room until you have surveyed the entire floor.

Steps for Leveling a Wooden Subfloor

You’ll need:

A random-orbit sander Coarse (60-80 grit) sandpaper Electric/cordless driver drill Flathead screws long enough to penetrate the subfloor into the floor joists Wet/dry vacuum

Steps for Leveling a Concrete Floor

You’ll need:

Angle grinder or floor grinder Diamond grinding wheel Wet/dry vacuum, ideally equipped with a HEPA filter Respirator

How to Fill in the Low Spots

In part, the type of finished flooring you’ll be installing can determine how you fill the low spots. Floating floor systems, such as laminate or vinyl, can sometimes be supported by stapling layers of builder’s felt (tarpaper) onto low spots on a wood subfloor. However, the amount of trimming and rechecking can get tedious. A faster solution that works for all types of flooring on both wood and concrete subfloors is to use a self-leveling underlayment. Available as either pre-mixed or a dry mix, it’s a cement-based material meant to be mixed (if required), poured, then troweled into low spots. Some underlayments are universal, (they can be used beneath any type of flooring), while others are more material-specific, so be sure to read the fine print before purchasing. Most self-leveling products also require the use of a latex primer that strengthens the bond to the subfloor.

You’ll need:

Mason’s trowel Bucket, electric drill, and mixing paddle (for dry mix underlayments) Wide trowel for smoothing Underlayment primer