Quality cement repair or concrete restoration depends on bonding new cement to the old, seamlessly. Proper cement repair can leave a smooth, good-looking result and last 20 to 30 years without needing to be replaced or repaired again. Careful planning in concrete restoration is paramount to foundation repair that can save thousands of dollars by avoiding costly repairs later.
Concrete is comprised of four elements: sand, gravel, water and cement. Cement crystals chemically react with water to bond sand and gravel together. Cement repair fails when the new and old cement fails to bond property, so the best way to ensure that a concrete restoration project is a success is with a cement patching compound.
It is possible to buy and mix the raw materials for a cement repair job, or purchase premixed cement. Choosing the proper gravel, sand and Portland cement is more time-consuming, but less expensive and generally results in a cleaner, more uniform look. Portland cement is the most common type of cement on the market.
For most concrete repair, mix three parts gravel, two parts sand, and 1.5 parts cement. When repairing patches that do not require gravel, mix 2.5 parts sand to one part cement. Choose appropriately-sized gravel to match with the existing concrete.
Attaching new cement to repair previously-shaped concrete like edges, corners, steps or sidewalks requires a pin, like a reinforced steel bar. The bar's rough exterior gives the new concrete extensive surface area to grasp, making the patch more long-lasting. If the old concrete allows the space, use a half-inch hammer drill bit to drill a three- to four-inch deep hole. Use a four-pound hammer or heavier to drive in the half-inch steel rod. Measure the length of rod you need first as cutting the rod after it has been inserted could weaken the older concrete or cause the new concrete to break away.
Before starting, clean and dampen the old cement. Apply a thin coat of cement paint to the surface. Paint any steel pins with metal primer to prevent the rod from rusting and cracking the concrete later. Apply a generous layer of cement, then add the mixture of sand, gravel and cement to repair the crack, hole or surface.
When finishing, drive the gravel pieces a quarter-inch below the surface by rubbing a flat board over the surface. The best time to do this is as you initially pour the concrete. The process will bring the sand and concrete to the surface, resulting in a smooth, even look.
Cool and damp weather is the best time for outdoor cement repair. Avoid warm, rainy or breezy days for this type of common home repair. If you must work on a hot day, keep a close eye on the cement as it sets and repeatedly smooth the settling concrete. As the cement settles, it may bleed out water. Do not use a board or trowel to force the water back into the concrete as this will weaken the surface concrete over time. Simply let the water evaporate.
After applying the new layer, cover the patch with plastic to prevent premature drying. Apply water to the new patch regularly for at least a week. New cement takes up to three months to properly cure and dry. It may take this long before the cement repair looks indistinguishable from the old concrete.