Concrete Steps for Mortar-Patch Repairs

Whether you’re fixing a walkway, steps or the floor, concrete repair techniques are essentially the same.

Tools and Materials

The basic materials that you’ll need for most jobs are patching mortar and liquid bonding agent, which helps the new patch stick to the old concrete. You’ll have to mix the mortar with water as directed. You can use an epoxy or latex patching compound instead of patching mortar for small jobs. These compounds form a stronger bond, do not require a bonding agent and are self-curing. But they are expensive for large jobs.

A flat and a pointed trowel are the essential tools. You may also need a light sledgehammer and cold chisel to remove old loose concrete. If you need to make a form for a step, you’ll need some scrap wood, motor oil and duct tape. You’ll also need some burlap or white plastic bags to cover the new concrete while it sets.

To protect yourself, wear safety goggles, heavy-duty work gloves and a dust mask.

Filling Cracks

* Fix a hairline or narrow crack (one-eighth-inch or less) with polyurethane caulk. It’s sold in cartridge form, for use in a caulking gun, at home supply centers. Clean out the crack with a wire brush, apply the caulk and smooth it with a putty knife.

* On a wider crack, use a light sledge and a cold chisel to chip away loose concrete and enlarge the crack so that it’s 1 inch deep and at least 2 inches wide. Make the crack wider at the base than at the surface; this technique, called undercutting, helps lock the patch in place.

* Brush away the loose debris thoroughly or remove it with a shop vacuum. Scrub the crack with a solution of strong detergent and water.

* Using a trowel, coat the still-damp crack with bonding agent. Apply the patch mortar while the bonding agent is wet.

Fixing a Broken Corner

* Chip back to solid concrete so the patch will hold. Brush away debris, and coat the surface with bonding agent.

* Tape scrap lumber around the corner to make a form. But first coat the inside of the lumber with motor oil to keep the patch from sticking.

* With a pointed trowel, build up patch mortar in the shape of the original corner. Use a small board to pack down the patch mortar and remove all bubbles.

* Fill the area to the top, flush with the rest of the step. Level the patch with the edge of a straight wood board.

* Wait at least 30 minutes before removing the form.

Mending Step Edges

* Chip away loose concrete. Undercut a V-shaped groove in the step edge. Clean and moisten the repair area.

* Prop an oiled board the height of the step against the step with concrete blocks.

* Coat the repair area with bonding agent.

* Use a pointed trowel to apply patching mortar. Prod the mortar with the trowel tip to remove bubbles.

* Smooth the patch to compact it and make it flush with the rest of the step. Round the edge of the patch to match the rest of the step.

* Allow about an hour for the patch to set, then carefully remove the board and touch up the area that was covered by the board with a flat trowel.

Curing

* To cure properly, mortar must be kept wet. Soak a patch with a fine mist from a garden hose three times a day for the first three days. Then moisten it twice a day for a week. Water evaporating too quickly from the concrete will weaken the patch, so cover the patch with wet burlap or a white plastic trash bag. It takes about a month to cure thoroughly. Keep traffic off it for three weeks, if possible.