What Would Bob Do? Leveling a Concrete Floor

There are a number of options for leveling a concrete floor. Read on to learn which approach is best for your needs.

How to Level a Concrete Floor

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I’d like some advice on how to level a concrete floor. We plan to finish the basement in my house, and there are going to be a couple of sump pumps, so we no longer need the old drain in the middle of the floor. Thanks!

There is no one way to level a concrete floor. Of all the methods available to do-it-yourselfers, which should you employ? That largely depends on how level you want to make the concrete. And that question, in turn, hinges on a related but different question: What type of flooring do you plan to install in your basement?

If you envision carpeting or another type of floor that forgives minor variations in subfloor grade, such as engineered wood or click-and-lock vinyl, then you can probably opt for the least labor-intensive method. Here, a concrete grinder would do the bulk of the work. (You can rent this tool from your local home center.) You’d use it to grind down the most prominent ridges in the floor. To finish the job, you would then mix up a small batch of concrete and use it to fill in any dips or depressions.

If you want to install tiles that glue down, things get a bit trickier. For a successful installation, the concrete floor beneath the tile needs to be more or less perfectly level and smooth. That’s true for compact tiles and even more critical for larger ones, including the popular 1-by-2-foot size. With small tiles, the maximum differential between the lowest and highest point on the floor is 1/4 inch per 10 feet; with larger tiles, the acceptable differential is a mere 1/8 inch per 10 feet. To achieve such flatness, use a self-leveling compound. These come in powdered form and are mixed with water and a fortifying agent. You end up with a thin liquid that when poured from a bucket flows across the existing uneven concrete. Gravity will bring the liquid to a level, but you can help the process along with a broom or trowel.

When it comes to mixing and applying the self-leveling compound, closely follow the manufacturer’s instructions, because every product differs slightly. Generally speaking, though, no matter what compound you choose, you’ll need to take similar steps to prepare the basement beforehand. For one thing, it’s important to remove any flaking paint or loose adhesive from the floor to ensure that the compound can get a good grip on the concrete. Also, so you don’t need an excessive quantity of compound, it’s not a bad idea to grind down any spots on the floor that are especially high. And of course, if there’s a drain—and you mentioned that there is one—it must be capped and sealed around the seams of its cap. Word to the wise: Wear cleats in case you need to walk across the compound while it’s still wet.

Once the self-leveling compound has set, you can proceed to install your chosen flooring. Alternatively, if you’ve had enough DIY for now, remember that you can eschew a finished floor, opting instead to stain, paint, or polish the compound that now forms the top layer of your concrete basement floor slab.