Concrete Repair Acton MA
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Concrete Patching and Repairing
This article provides a short primer on the causes of stable cracks and common damage, as well as the step-by-step process for repairing specific problems. Why Does Concrete Crack? Shrinkage is a main cause of cracking, according to ConcreteNetwork.com. As concrete hardens and dries, it shrinks. Concrete slabs can shrink as much as half an inch per 100 feet. This creates forces in the concrete that literally pull the slab apart. Cracks are the end result of these forces. The bottom line is that, although adding water makes concrete easier to handle and install, a low water-to-cement ratio improves concrete quality dramatically. Excess water greatly reduces the strength of the concrete; the wetter or soupier the concrete mix, the greater the shrinkage will be.
In addition to shrinkage, other factors that contribute to cracking include rapid drying of concrete, using concrete of improper strength, lack of control joints, friction between the sub-base and concrete slab, and weather conditions. According to the American Concrete Pavement Association, weather almost always has some role in the occurrence of uncontrolled cracking. Air temperature, wind, relative humidity and sunlight influence concrete hydration and shrinkage. Under warm, sunny summer conditions, the maximum concrete temperature will vary depending on the time of day when the concrete is paved. Concrete paved in early morning will often reach higher maximum temperatures than concrete paved during the late morning or afternoon, because it receives more radiant heat. As a result, concrete paved during the morning will often exhibit more instances of uncontrolled cracking. After the concrete sets, uncontrolled cracking might also occur when temperature changes result in differential thermal contraction, or different contractions for different parts of the concrete. What Can You Do About It? As with any building job, the best place to start is before construction. Make sure you hire a reputable concrete contractor who is familiar with your area. Ask them about the mix they are using and request that they use a stiff mix, or one with slightly less water. This will take more work, but will result in less cracking. Talk to your contractor about taking enough time to cure the concrete properly, and make sure that adequate control joints are installed for walks and patios. Check out the material being used for a sub-base and make sure that it is appropriate for your area. Do some research and at least be familiar with the recommended procedures.
You can consult the Ready Mixed Concrete Association in your area for more information. Taking some time up front can help avoid problems later. Nevertheless, we still have to deal with concrete that was either installed years ago, or more recently but poured incorrectly. Fortunately, repairing concrete is not a difficult task if you follow the directions and take your time. Pick the right day - The best time to patch concrete is during the spring or fall, when the temperature is about 50° to 60° F. It is best to avoid hot, sunny or windy days, as these conditions can remove water rapidly from concrete patching compounds. More importantly, the concrete you are trying to patch will likely be very dry and thus absorb water from the patching compound like a sponge. As stated above, water is one of the most crucial ingredients for a good concrete mix. Not only does it make the mix workable, but it is also a chemical ingredient necessary to make the compound strong. Make sure that you follow the directions carefully to ensure that you add the correct amount of water. Choose the right patching material - There is a bewildering array of concrete patches available on the market, ranging from traditional dry mixes to more modern caulking compounds. Unfortunately, there is no single best compound to use. Consider purchasing patching materials that contain polymer additives or blended cements, because they stick much better to older concrete. Look for the words "acrylic," "vinyl" or "gypsum cement" on the label.
You can also use liquid additives. Some of these additives are mixed with the patching compound, while others are applied to the surface to be patched. You might also find a 100 percent epoxy patching compound. Prepare the area and take appropriate safety precautions: Make sure that the area is clean and free of all loose material and dust. Wear safety goggles if you are chiseling, and rubber gloves if you will be handling the compound. You should also use a mask when mixing dry materials. You are now ready to tackle the patching job. Repairing Cracks You can repair cracks in concrete with a grout made of portland cement and water. Add just enough water to the cement to form a thick paste. You can also use one of the premixed compounds or a caulking material. Moisten the old concrete along the hairline crack with water several hours before adding the grout. Although the old concrete should be moist, no water should be standing on the surface when the grout is applied. Cracks in sidewalks that are larger than hairline cracks must be enlarged with a cold chisel and hammer before they can be repaired satisfactorily. Undercut the crack wider at the bottom than at the top to a minimum depth of 1 inch. The depth of the undercutting depends on the size and depth of the crack to be repaired. Remove all loose material and brush the area with a wire brush or garden hose. For hairline cracks, apply the grout with a putty knife or pointing trowel. Force the grout into the crack as much as possible. Then smooth it off so it is level with the original concrete. For larger cracks, consider using one of the many types of concrete adhesive. Acrylic resin, a milky fluid, is one common type. Brush the adhesive into the undercut area and allow it to dry until it becomes tacky.
For small patching jobs, use a premixed concrete patch. If you use ready-mix concrete patch, all you need to add is water. If you mix your own concrete patch, use one part portland cement to 2 1/2 parts of fine, clean sand. Heavier concrete patch jobs call for one part portland cement to two parts of sand to three parts of gravel. Tamp the concrete patch mix tightly into the undercut area. Be sure to fill all areas completely. For vertical surfaces like steps, take a piece of wood and place it against the area to be refinished. Set the wood in place with bricks, concrete blocks or other heavy objects. This will act as a form to hold the concrete in place while it sets. When the mixture begins to set, smooth it down with a metal trowel for a smooth finish, or a wooden float for a rougher surface. After the patch is completed, allow it to dry for about two hours. Then cover the patched area completely with plastic sheeting or boards. Keep the area covered for about five days. Lift the cover once each day to lightly wet down the repaired area, permitting the new concrete to cure correctly. Repairing Holes If the hole is extremely deep and large, you must undercut it as previously described and fill the area with a gravel mix. Small, shallow holes in flat-surfaced concrete - such as driveways, patios or sidewalks - can easily be repaired with latex cement. If the hole is small and shallow, no chipping is required. Clean the hole with a wire brush and wash the area with a garden hose. Mix the latex cement to form a heavy paste, and apply the paste in approximately quarter-inch layers until it reaches the same level as the original concrete. Smooth each layer with a trowel and allow to dry partially before applying the next layer. Then, smooth out the area with a trowel or float as described above.
Once your concrete is repaired, you need to think about maintenance. You may want to consider sealing the concrete if it is exposed to varying weather conditions. Sealers repel water and dust, as well as provide protection from abrasion, sunlight, dirt and grime, oil, grease, rust, acid, chlorine, fertilizer stains, sprinkler-water residue and mildew, as well as stains from most other organic matter. Purchase the best sealer for your situation and apply as per the directions. By following all of the steps outlined above, you will ensure that you have a concrete repair that is as good as the original and will last well into the future. Barry Chalofsky is an environmental land planner and the author of The Home and Land Buyer's Guide to the Environment. For more information, visit his website at www.erols.com/profed.