How to Level a Concrete Slab Before Flooring


When installing new tile, hardwood or laminate flooring over a concrete slab subfloor, it is critical to have a smooth and level surface. If it is not level, over time, tiles can become loose and cracks can develop within the grout joints. Installing laminate or hardwood flooring over a slab with high and low areas can create a spongy feel and creak as you walk over it. The process is not too difficult, but does require a few special tools and some careful preparation.

Things You'll Need

  • Floor scraper
  • Chemical adhesive remover (optional)
  • Broom
  • Vacuum
  • Aluminum straight edge
  • Flashlight
  • Pencil
  • Sponge mop
  • 5-gallon bucket
  • Drill with mixer attachment
  • Leveling compound
  • Flat trowel
  • Prepare the concrete slab by removing any adhesive that remains from previously installed flooring. Use a floor scraper; if you choose to use a chemical adhesive remover, read and follow the instructions. Thoroughly sweep and vacuum the slab.

  • Lay an aluminum straight edge across the slab. This is a long, flat metal bar that can be rented or purchased from most home improvement stores. Take a flashlight, lay it on the slab and point the light beam toward the bar. Take note of where the light passes under the straight edge. These are low areas or dips in the slab. Circle these areas with a pencil. Move the bar around to different areas of the floor and mark all low spots.

  • Wet the slab's surface with a sponge mop. This helps the leveling compound adhere to the concrete.

  • Mix small batches of leveling compound because it sets up quickly and you need to work fast. Use a drill with a mixer attachment and follow the instructions exactly. Water that is too hot or cold can affect the setup time. The mixture should have the consistency of pancake batter.

  • Pour the mixture into the circled low areas. Use a flat trowel to spread the compound and feather or blend it into the surrounding area. Repeat the process of mixing small batches, pouring it onto low areas and blending it into the surrounding areas until all the low areas have treated.

  • Clean all the tools and equipment with water. If this is not done immediately, the mixture will set up and make it nearly impossible to remove later.

  • Allow the areas to thoroughly dry before applying any flooring. The time will vary depending on the temperature and the amount of humidity in the air. Typically, you can walk on the concrete slab after two hours and flooring can be installed after 12 hours.

Tips & Warnings

  • Using box fans can speed up the curing process of the leveling compound mixture.
  • Special latex primer products, found at most home improvement stores, can be used to ensure a good bond between the slab and the leveling compound.

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  • Photo Credit Jupiterimages/Creatas/Getty Images
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