Guide to Repairing a Square of Concrete

Concrete Evaluation

• Before attempting to repair damaged concrete, you must determine if the damage is superficial or structural. Superficial cracks don’t compromise the concrete structure. If the cracks appear stable, don’t have rust stains around them and no reinforcement materials are visible, it is usually safe for you to make the repairs. Cracks surrounded by rust or those that reveal reinforcing materials indicate structural damage and should be repaired by a mason experienced in structural analysis and renovation.

Hairline Cracks

• Hairline cracks are easy to fix with a mixture of Portland cement and water. Mix the two components to a thickness that is spreadable but has enough viscosity to cover the crack. Apply water to the concrete surrounding the crack and let it rest for several hours. This keeps the dry concrete from leaching the moisture from the repair grout. After the moistening is complete, clean the hairline crack and area around it with a wire brush to remove debris that may interfere with the adhesion of the patch material. Use a putty knife or small trowel to firmly press the grout into the crack and smooth it level with the existing surface. After it dries for a couple of hours, cover the crack with a board or sheet of thick plastic and let it cure for five days, remoistening the repaired area once a day.

Larger Cracks

• To ensure a solid repair in larger cracks, enlarge them with a chisel and hammer, remove all the debris with a wire brush and flush the crack with pressurized water from a garden hose or air from a tire pump. The crack should be larger at the bottom of the crevice to facilitate bonding. Brush the inside of the fissure with concrete adhesive and let it dry until its surface is sticky. Fill the crack with pre-mixed concrete mixture or make your own patching material by mixing one part Portland concrete and one-and-a-half parts fine sand with enough water to make it appropriately thick for patching. Pack the crack with the cement and level it off when it starts to harden. Proceed with the same drying and curing process used for hairline cracks.

Non-Repairable Concrete

• Some cracks are so serious the concrete cannot be repaired and requires replacement. Deep cracks caused by earthquakes, the weight of heavy trucks or machinery or extensive erosion require concrete replacement. If the sub grade is faulty and the concrete has sunk because of loose dirt or water underneath it, replacement is necessary. Concrete that has been cracked or broken by frozen earth pushing it upward during heavy frosts cannot be repaired.