CONCRETE REPAIR 45 45 Call your local White Cap branch for project pricing Curing Your Repairs The fi nal important step of the repair process is to cure the repaired areas. You can use a wettened burlap sack or piece of cheesecloth. Some contractors will use a spray-on curing compound. Three cautionary suggestions on this type of repair: 1. It’s important to refer to the manufacturer’s recommendation on whether to or not prewet the repair area. 2. Try to not place or smear the repair mortar over a larger area than necessary. 3. Purchase only enough material for the project at hand. The material in leftover packages can be less ef ective if too much time lapses between uses. If the surface has too many popouts for individual repairs, or if during the repair the surface suf ered delamination, contractors should consider using a thin-bonded concrete overlay. This type of repair will leave a more consistent look, desirable on exposed fl oors. First address the removal of all unsound material in each popout as previously described. Then outline the entire area that will be receiving the overlay. The area should receive a thorough pressure washing to remove all dirt, chemical residue, and loose concrete on the slab’s surface. Most overlay material manufacturers also recommend that the entire area receive an aggressive treatment, such as grinding or shotblasting that results in a uniformed roughened surface profi le. Material manufacturers often specify the exact requirement of the fi nal prepared surface referring to the industry standard ICRI Concrete Surface Profi le Guidelines. Matching the specifi ed profi le is necessary to achieve maximum bonding, and is determined by the overlay material. Refer to the manufacturer’s recommendation with respect to prewetting the repair area. And after the overlay’s placement, follow recommended curing procedures. Cosmetic Cracking Blemishes Plastic shrinkage and drying shrinkage cracks dif er from popouts because they emerge during or soon after the slab’s hardening. Unlike popouts, these cracks are the result of improper curing that occurs as the concrete hardens. The cracks are not localized and can extend across the slab. The cracks are most often shallow and tend to be wider at the surface and narrower into the slab. Crazing cracks occur when the surface of the concrete dries and contracts at a dif erent rate than the underlying concrete. To reduce/ prevent crazing, don’t allow the surface to be exposed to low humidity, hot air, solar heat, and similar elements. After fi nishing, don’t wait too long before you start your cure. If all the surface moisture evaporates before curing it can result in cracking, crazing, etc. Often times these types of cracks are left untreated, as they normally do not af ect the slab’s service life. Yet on most exterior applications, it’s best to repair these cracks to prevent water intrusion that could lead to rebar corrosion, uneven settlement, or slab movement. On interior applications, unrepaired exposed cracks can be unsightly, and sometimes lead to tripping hazards. Repairing Static Cracks Contractors should approach the repair of both plastic shrinkage cracks and drying shrinkage in the same manner. The surface preparation of both begins by removing any debris that may have fallen into the crack’s openings. Often curing compound, densifi ers, and sealers from the slab’s placement may have fi lled in portions of the opening. Some contractors may sawcut the crack to create a consistent width. This action helps with aesthetics and adhesion of the fi lling agent. The next step is a vigorous cleaning with a wire brush or oil free sand blasting. When the crack’s channel is fi nally shaped, use a high-pressure vacuum to extract any dust and residue. Avoid using compressed air or water blasting to clean the cracks. Since these cracks are often shallow, it’s best to fi ll the entire cavity with repair material. Most repair materials can be applied to crack depths from 1/8” to 1”. Do not use backer rod to reduce volume. If the channel is deep, use dry silica sand to fi ll the bottom of the joint. The sand prevents 3-sided adhesion. The cracks should be overfi lled and allowed to cure for approximately 1 hour and up to 24 hours before shaving fl ush with a fl oor razor scraper. The top of the repair material should be fl ush with the slab’s upper surface. The most common repair material is a two-component hybrid urethane joint fi ller. Opt for an ultra-low viscosity material that penetrates deep into cracks, mending them back together. If necessary, contractors can mix the liquid with aggregate to make a tough mortar. Just prior to the crack fi lling process, technicians should be absolutely sure to completely and thoroughly mix the two components together following the manufacturer’s requirements for mixing sequence and times. The sample should be deposited into a waste container. With the proper tools and materials, you can execute durable, aesthetically pleasing repairs of common concrete surface blemishes. The general consensus is to deal with cracks and blemishes in a timely manner to improve aesthetics (on visible fl atwork), and prevent subsequent damage. And even more importantly, keeping our customers happy often translates into repeat business and new customers through word of mouth.
