Patching and Repairing a Basement Concrete Floor

Before you can install your new floor, you’ll need to examine your concrete basement floor to ensure it meets the finished floor’s installation requirements.

After a long deep search and with my 5 years of work in this field I will resume my experiences and the tricks in this article and answering these questions: How do you fix a crumbling concrete floor? Why is my concrete crumbling? What causes cracks in a basement floor? and more.

Any basement floor should be free of cracks and holes, and it should be level. If a concrete floor has a crack but the area is firm, you can repair it with epoxy injection as for a wall. But if the damage covers a fairly large area, chip it out and pour concrete. If your floor feels wobbly when you walk on it, call in a pro for evaluation, you may need to tear out and repour, regardless of what finished floor you’re going to lay down. You can also fix a floor that’s not level.

Chipping and filling a damaged area

  • To repair a damaged, raised, or otherwise unsuitable area for the flooring you want to install, you could use a masonry saw to cut an outline that is about 2 in. deep. Or, use a rented electric jackhammer to chip the area out, taking care not to dig too deep. (Most basement floors are 4 in. to 6 in. deep, but in an older home, it may be only 3 in. deep.)
  • To keep the dust down, have a helper hold a vacuum hose near the chipping blade. Remove all material to a depth of at least 11⁄2 in. below the surrounding surface. Vacuum the area and slightly dampen it. Mix batches of high-strength concrete and pour into the area.
  • Use a board that spans across the patch to roughly “screed the concrete”: drag it across, then use a sawing motion to push the stones down.
  • Smooth the surface to suit your needs. Use a wood or magnesium float, then a steel trowel, to bring the liquid to the surface and to feather out the patch where it meets the surrounding floor.
  • The slower the concrete cures the stronger it will be, so cover with plastic or spray with a mist every 8 hours or so to slow down the curing.

Leveling with self-leveling compound

  • If an area of the floor dips down more than 1⁄4 in., it will adversely affect almost any kind of flooring. Check your floor by dragging an 8-ft. level or a long, perfectly straight board across it in two directions at all points.
  • Where you see a significant rise, just chip it away if you can; otherwise, follow the steps on the previous page for chipping and filling. Where you see a dip, fill it with “self-leveling compound.” This product does not quite live up to its name—you can’t just pour it and walk away—but it is easy to level and feather out. Mix a batch according to directions, so it is pourable and pours into the area.
  • Smooth it with a trowel.
  • Take care to feather the edges as finely as possible. Avoid overworking the surface more than a few strokes will bring too much fine material to the surface, weakening it. Check with a straightedge to make sure you are filling the indentation but not raising the patch above the floor surface.

OR

  • Test the floor to see how level it is. Use a laser level to project a level line on all walls. Mark the line and then measure down to the floor. Compare measurements to determine if the floor is level. If you are installing a subfloor, you can correct the unevenness by shimming under low areas. But if the floor height varies by more than an inch, you should pour floor leveler compound in the low areas. In more extreme cases, you’ll need to resurface the entire floor.
  • Break up and remove very high areas or eruptions, and patch the area with concrete that is leveled with the surrounding surfaces. Use a rental jackhammer to break up the concrete. A hand maul and cold chisel also may be used if the area is not too large: most concrete basement floors are only 3 to 4″ thick.
  • Grind down high spots if they are small and far apart. A rented concrete grinder makes quick work of the job. Even larger areas can be ground down if your ceiling height is already limited (less than 7 ft.).

How to Repair Floor Cracks

  • Prepare the crack for the repair materials by knocking away any loose or deteriorating material and beveling the edges down and outward with a cold chisel. Sweep or vacuum the debris and thoroughly dampen the repair area. Do not allow any water to pool, however.

  • Mix the repaired product to fill the crack according to the manufacturer’s instructions. Here, a fast-setting cement repair product with acrylic fortifier is being used. Trowel the product into the crack, overfilling slightly. With the edge of the trowel, trim the excess material and feather it so it is smooth and the texture matches the surrounding surface.

How to patch a small hole

  • Cut out around the damaged area with a masonry-grinding disc mounted on a portable drill (or use a hammer and stone chisel). The cuts should bevel about 15° away from the center of the damaged area. Chisel out any loose concrete within the repair area. Always wear gloves and eye protection.

  • Dampen the repair area with clean water and then fill it with the vinyl concrete patcher. Pack the material in with a trowel, allowing it to crown slightly above the surrounding surface. Then, feather the edges so the repair is smooth and flat. Protect the repair from foot traffic for at least one day and from vehicle traffic for three days.

How to Patch a Large Hole

  • Use a hammer and chisel or a heavy floor scraper to remove all material that is loose or shows any deterioration. Thoroughly clean the area with a hose and nozzle or a pressure washer.

OPTION: Make beveled cuts around the perimeter of the repair area with a circular saw and masonry-cutting blade. The bevels should slant down and away from the damage to create a “key” for the repair material.

  • Mix concrete patching compound according to the manufacturer’s instructions, and then trowel it neatly into the damaged area, which should be dampened before the patching material is placed. Overfill the damaged area slightly.

  • Smooth and feather the repair with a steel trowel so it is even with the surrounding concrete surface. Finish the surface of the repair material to blend with the existing surface. For example, use a whisk broom to recreate a broomed finish. Protect the repair from foot traffic for at least one day and from vehicle traffic for three days.
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