How to Level a Subfloor to Lay Flooring

We’ve previously discussed the importance of underlayment when laying any type of flooring but before you can even get to that step in the process, it’s essential that you level the subfloor. This will not only help your flooring last longer but it can also help to maintain the look of the surface flooring you choose. When you’re spending as much time and money as a new floor costs, you want to do everything you can to ensure that it remains in tip-top shape as long as possible. Leveling flooring can be a DIY project but if you have big peaks and valleys, foundation or structural problems, or termite damage, you should call in a professional. If that is not the case, however, you can take on the job yourself by following our guide on leveling a subfloor to lay flooring.

How to level a subfloor step #1: Remove the existing flooring

First, start by removing the old flooring and underlayment to reveal the subfloor. Bear in mind that when removing old flooring and leveling subfloors, the old flooring could potentially contain asbestos. Wear the proper safety equipment and consult a professional for help with safe removal and disposal of the materials. 

How to level a subfloor step #2: Check the subfloor’s level

It may not be clear just upon looking at the subfloor how high or low some spots are. To check, place a long level or straight pipe on the subfloor. Move it to different areas and mark any spots with a pencil or marker where you find that are higher or lower than normal. Most subfloors will have at least a few spots with slight variations.

How to level a subfloor step #3: Repairing & cleaning a concrete subfloor

If your subfloor is made of concrete, use a concrete grinder for wide, open spaces and be sure to wear a respirator as this process can create a lot of dust. As you grind the concrete subfloor, continue to check the level. 

When you are finished, vacuum the floor thoroughly with a wet-dry vacuum or sweep up the dust with a broom. Make a final check using the level to make sure that all the high spots are gone. 

How to level a subfloor step #4: Repairing & cleaning wood or concrete subfloor

Leveling low spots in concrete or wood subfloor

In order to repair low spots in wood or concrete subfloor, you’ll need either a floor patch product or floor leveler specifically made for underlayment. Floor levels are cement-based products that either come premixed or as a dry substance that you mix with water. Floor patches help to repair cracks, small dips, holes, and other minor imperfections. With either product you choose, make sure to follow the manufacturer’s instructions. 

Pour the floor leveler onto the subfloor and smooth it out using a trowel. Gravity will pull the liquid substance into the low-lying areas. Remove any excess and feather it around the edges so that it blends seamlessly with the rest of the floor. 

Let it dry overnight or as indicated in the manufacturer’s instructions. As it dries, sand down any high spots to make them flush with the rest of the subfloor. Use a wet-vacuum to clear up dust and debris and use a level to be sure all the low spots are gone. 

Leveling high spots in concrete or wood subfloor

If the subfloor is plywood or particle board, start by screwing down loose boards and add more wood screws where needed to secure them. Replace any nails with screws as nails will just continue to come loose. Remove any stray nails or staples. 

When you are leveling subfloors made of wood, you will need to sand down the high points using a sander. 

Check the floor with a level throughout the sanding process to make sure it’s even. 

When finished, vacuum the floor with a wet/dry vacuum or sweep up the dust with a broom. Make a final check with the level to ensure that the subfloor is now even.