Patching & Repairing Concrete
By Monte Burch
First-aid for Concrete Construction.
Concrete is one of mankind’s greatest inventions. Very durable, it can also be aesthetically pleasing. Concrete is also often a major building material in and around homes. Over time, however, concrete can deteriorate. Patching and repairing concrete can be easy or difficult, depending on the project and the amount of deterioration. Most repair projects are fairly simple using some of the specially formulated patch and repair products available these days.
Concrete is basically made by mixing together four ingredients, Portland cement, sand, crushed stone or gravel and water. These ingredients must be mixed in the proper proportions. You can mix the ingredients yourself, or purchase premixed products, blended for specific chores.
Specialty concretes are very user friendly, and have distinct characteristics such as fast initial or final setting times, high early or final strength, or increased resistance to cracking and chipping. It’s important to choose the correct specialty concrete product for the specific job. Regardless of the product chosen, it’s also extremely important to follow the instructions and safety precautions on the package.
You’ll need a few tools, including a cold chisel, ball-peen hammer or 8-pound sledge for larger areas, protective goggles and gloves. A brush and broom or hand vac is also necessary, as is a plasterer’s trowel and pointing trowel. If you’re resurfacing steps and slabs, you’ll need an edger as well. You may also need lumber for forming some repairs. And, of course, you‘ll need the appropriate repair product. From the Quikrete Company this includes Concrete Bonding Adhesive, Acrylic Fortifier or Vinyl Concrete Patcher or packaged concrete. For interior floors you’ll need Self-Leveling Floor Resurfacer.
It’s extremely important to prepare the repair area properly before applying the concrete product. Remove all cracked and crumbling areas. On small areas you can do this with the point of a heavy-duty trowel. For larger areas use a sledge and cold chisel to break away any thin or loose edges. Then sweep, vacuum or hose away all dirt and debris down to a solid base.
To patch the crack shown in this article, we used Quikrete Vinyl Concrete Patcher, a self-bonding cement mix made specifically for repairing broken, chipped or loose concrete and masonry, as well as filling medium to large cracks. The cracks shouldn’t be deeper than 2 inches. The material is available in tubs or a 40-pound bag. It will adhere to all properly cleaned surfaces and can be troweled to a feather edge of 1/16 inch. All you need to do is add water.
Again, the first step is to properly prepare the surface. Use a chisel to remove all cracked and crumbling materials, squaring off the edges. Even better yet, undercut the edges using the chisel and hammer. Use a wire brush to remove any crumbling materials and to roughen the surface if it is finished smooth. The material should not be applied over painted surfaces. Clean away all debris, and then further clean with Quikrete Concrete and Asphalt Cleaner. Rinse with water. Mix only the amount of material that can be applied in 30 minutes, according to the manufacturer’s instructions. By design, Vinyl Concrete Patcher is a “stiff mix.” It is best to keep the trowel clean and dry while applying the mix. This prevents the mix from curing on the tools.
Before application dampen the area with clean water, but remove any standing water. Apply the mix with a trowel, using heavy trowel pressure to force the mixture into the crack. Overfill slightly and then trowel smooth to match the surrounding concrete. If cracks are deep it may be necessary to apply in 1/4-inch deep layers. Allow the material to dry for two hours between layers. Clean the tools immediately with water.
Small cracks are easy to patch with Quikrete Gray Self-Leveling Concrete Crack Seal. The product comes in a squeeze tube, and fills and seals cracks in concrete up to 1/2-inch wide. For large or deep cracks, you can use Quikrete Sand Mix or the company’s Concrete Bonding Adhesive.
Larger repair jobs, such as broken corners or slabs of walks, usually require reforming. First step is to remove the broken area down to the gravel fill. If the gravel fill has deteriorated, dig down a couple of inches below ground level and add a gravel base. Use 2-by-4 or other material to reform the area. The tops of the form boards should be even with the top edges of the adjoining concrete surface, as well as even with what will be the new repaired surface. Forms should be level and should follow the natural grade. Stakes should be placed every four feet and cut off even with the top edges of the forms.
Vinyl Concrete Patcher or packaged concrete can be used, the former, however, will bond more readily to the existing concrete. Mix the concrete product and trowel or shovel into the form. Roughly smooth up with a trowel, then cut around any forms with an edger. Allow the concrete to stiffen slightly, waiting until all water has evaporated from the surface. Once the surface turns dull, smooth and compact the concrete with a trowel. Keep the trowel pressed firmly down on the surface and flat. Reuse the edging tool around the edges to smooth them up. For a textured, non-skid surface, use a wood float for finishing.
Keep the concrete damp for 5 to 7 days to help the hardening or curing process. Concrete that has been moist-cured will be approximately 50 percent stronger than that exposed to dry air.
A similar problem is a walk that has uneven slabs. These can be reformed and repaired, again using form boards. If the area to be resurfaced is greater than one inch, apply a coat of Concrete Bonding Adhesive to the cleaned surface using a roller or paint brush. When dry, fill the form with Sand Mix as directed by the instructions. Level and smooth with a trowel. Wait a bit until the surface water has evaporated, then finish troweling. For a sidewalk or steps, brush with a broom finish if you desire a roughened finish.
Spalled or flaked concrete surfaces can also be repaired quite easily. Apply a thin layer of Sand Mix with Acrylic Fortifier added at a ratio of one-half gallon Acrylic Fortifier to 80-pounds of Sand Mix and trowel smooth.
More Patching Products
Before constructing, repairing or renovating interior horizontal concrete slabs, consider Mapei’s line of concrete repair products. Mapecem 100 is a cost-efficient cementitious mortar that is ideal for a multitude of applications, including resloping floors; leveling low areas of floors; filling trenches, voids and honeycombs; and treating concrete defects. Fast-setting Mapecem 100 is formulated with Mapei’s High-Hydrated Cement Technology (HCT), allowing traffic within 3 to 4 hours of application.
The Mapei Planitop X product is a one-component mortar that blends with original concrete color. It can be applied vertical, horizontal or overhead. The smooth finish product features Easy Glide Technology that makes it extremely easy to feather out.
The Sakrete Company offers a complete line of crack-filling products as well as patch and repair and resurfacing products. For minor repairs of cracks and other imperfections, Sakrete mortar or stucco repair products come in convenient tubes. For larger cracks, Sakrete Concrete Crack Filler is a pourable, flexible concrete material for lasting repairs. T restore chipped, cracked and spalled driveways, walkways, slabs and steps, Sakrete Top ‘N Bond Concrete Patcher and Flo-Coat.