How to Repair Spalled Structural Concrete

Mark the spalled area of the concrete with a chalk line. The repair area must extend 2 inches beyond the spalled area and be formed of straight lines. Pull a chalk line from corner to corner of the repair area.

Cut along the chalk lines using a circular saw equipped with a diamond-tipped blade to a depth of 2 inches. Remove the spalled concrete from the repair area by holding a chisel against the concrete and striking the chisel with a hammer. Chisel the bottom of the work area to a relatively uniform level.

Prepare a bonding agent by combining equal parts of Portland cement and masonry sand in a bucket. Add enough water to form a thin, pourable mixture. Brush the bonding agent on all sides and the bottom of the repair area with a paintbrush. You must apply the repair concrete within 10 minutes of applying the bonding agent.

Mix a batch of concrete consisting of two parts Portland cement and one part masonry sand. Combine the dry ingredients in a 5-gallon bucket, using a hoe to mix them thoroughly. Slowly add one part water to the dry ingredients until the mixture is a medium consistency. If it is too dry, it will be unworkable and form a poor bond. If the mixture is too thin, the concrete will be weak.

Spread the concrete into the prepared repair area with a steel trowel, pressing down to eliminate air bubbles and gaps. Continue filling the hole until the concrete is level with the surrounding edges.

Wait 24 hours before allowing traffic on the repaired area. Allow the concrete patch to cure for three to seven days, spraying it every four to six hours with water to allow the concrete to obtain maximum strength.