level the bottom o the hole
Photo: Kenneth Chen
1. Use a hammer and a cold chisel to level the bottom of the hole and undercut its sides slightly so the patch can’t pop loose.
Simply pouring wet concrete into a hole in your driveway, sidewalk, or basement floor won't make for a lasting repair. You have to prep the edges correctly and use the right materials. Holes 1 inch or deeper require a concrete mix with coarse, crushed-stone aggregate, which bonds well with existing concrete. Shallower holes need a sand mix. Whichever type you use (they're both available at home centers), follow these steps.

1. Use a hammer and a cold chisel to level the bottom of the hole and undercut its sides slightly so the patch can't pop loose. Vacuum, then clean the area with water and a wire brush. Wipe clean.

2. Brush on a concrete bonding liquid, sold in bottles at home centers.

3. While the bonding agent is still tacky, mix the concrete with water and scoop some into the hole. Press it into the corners and against the edges with a trowel. Now fill the hole completely, leaving some material mounded on top.

4. Level the patch with a straight-edged board at least a foot longer than the width of the hole. Move it back and forth in a sawing motion. This will also push down the aggregate and make the final smoothing easier. When the surface loses its wet sheen and feels firm to the touch, smooth it with a magnesium or wood trowel, which won't interfere with curing. Work the trowel in a fanning motion to blend the edges with the existing concrete. Do this several times as the mix cures. To burnish the surface very smooth, use a steel trowel (shown) on the final few passes. For a texture, pull a damp push broom over the concrete. Wait at least 24 hours before walking on the patch and a week before driving on it.

TOH Tip: The temperature of the existing concrete must remain above 50 degrees for the first 24 to 48 hours after the patch is applied. The cooler the weather, the longer the curing time.

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