Strong as it is, concrete is brittle and prone to impact damage, especially on the lip of a step, as shown here. Preparation is the key to a concrete patch that lasts: the surface must be clean, and there must be enough of a ledge for the patching compound to adhere. If the damaged area is smooth, roughen it with a hammer and cold chisel to be sure the patching compound can get a good grip. (Wear safety glasses when you do this to protect your eyes from flying chips.)
If the patch is more than 2 inches thick, drill 1/2-by-2-inch holes in the step and set 1/4-by-3-inch bolts in compound in the holes to anchor the patch. Be sure to get a patching compound specifically formulated for repairing old concrete, and use concrete adhesive for extra strength, rather than water, when you mix it.
Step by Step 1. Remove all loose material with a wire brush. Then rinse with water to get rid of dust and dampen the old concrete so it won't suck moisture from the patching compound.
2. Brace a form board against the step riser so the top is level with the tread. Bricks or concrete blocks are cheap and effective braces. Mix enough compound with adhesive to fill the area.
3. Apply patching compound with a mason's trowel. When the patch firms, but before it dries completely (check the directions), remove the form and finish the surface to match the surrounding area. Round off the corner to make it more durable. Let the patch cure before you walk on it. Many packaged patching compounds are quick curing, and your renewed step may be ready to go by the next day.
TOOLS AND MATERIALS
Hammer
Concrete patching compound
Cold chisel
1/4-by-3-inch bolts or lag screws
Safety glasses
Board and bricks to brace the form
Drill
1/2-inch masonry bit
Wire brush
Mason's trowel
