MASCO Catalog: Construction Liquid and Powder

60 MASONS SUPPLY COMPANY Oregon (800) 537-3407 ♦ Washington (800) 537-6216 ♦ www.MASCO.net Clackamas | Eugene | West Eugene | Hillsboro | Medford | Portland | Salem | Ridgefield | Seattle | Tacoma | Woodinville Curing concrete is essential for good results and is the final and most important step in producing good concrete. Retention of moisture in fresh concrete during the hydration process builds strength, improves abrasion resistance and freeze-thaw resistance. If concrete is not cured, its strength can be reduced by up to 40% and can result in surface cracking, crazing, curling, and dusting. It is very important to cure the concrete immediately after finishing. Wet burlap, water spray and plastic sheets are effective methods of curing only if the concrete is kept constantly damp for 7 days. Otherwise, membrane applied curing compounds are preferred. The main performance specification for curing compounds is ASTM C-309. The specification states that curing compound shall not allow the concrete specimen to loose more than .55 kg of water per square meter of surface area in 72 hours. The white- pigmented compound shall exhibit a reflectance of at least 60% of that of a standard magnesium oxide reference plate. Types of curing compounds: Type 1 - clear or translucent without dye; Type 1D – clear or translucent with fugitive dye; Type 2 – white pigmented. The curing compound shall also be of one of the following classes: Class A – no restrictions on the vehicle solids material in the curing compound, typically wax based material; Class B – the vehicle solids material in the curing compoundmust be all resin. Remember, according to the ASTM Committee on Curing, no sodium silicate curing compound will meet the ASTM C-309 specifications. Water based products will need agitation before use. However, do not over agitate or induce air. Always apply the curing compound uniformly at the specified application rate, typically 200 sq. ft. per gallon. A major problem on most jobsites is the spraying of curing compounds at higher than recommended application rates. As the result over application causes the curing compound to dry improperly and it takes longer to breakdown and oxidize. A good rule of thumb on flatwork is to apply the curing compound heavy enough to create a slight flood of material on the concrete surface or, apply curing compound in two applications, one at right angles to the other. Most curing compounds, with the exception of sodium silicates will have to be removed before application of a liquid hardener, an epoxy or urethane coating, a cement based product, or a water repellent like a silane or siloxane. Resin based curing compounds will normally oxidize and begin to wear off in 60 to 90 days. This is predicated on the amount of sunlight and traffic the curing compound receives. Typically, stiff bristle scrubbing followed by pressure washing is sufficient after this 60 to 90 days period. Additional cleaning of the surface by high pressure water blasting with sand, shot blasting, or chemical removal may be necessary, if the curing compound was over applied, protected from sunlight and did not oxidize, or if it had less than 60 days since the application of the curing compound. Wax based curing compounds will not break down with exposure to sunlight like resin based curing compounds and will need mechanical removal methods like sand blasting, shot blasting, or hot water (170 degree plus) high pressure washing to remove from the surface. A good test to see if the curing compound has been removed is to place a few drops of water on the surface and see if the water is readily absorbed into the concrete. If the water droplets bead on the surface and do not absorb readily then additional removal procedure will be necessary. If additional treatment of concrete is required, always follow that manufacturer’s product recommendation for surface preparation procedures . The above recommendations are applicable for most applications; however refer to data sheets, installation guidelines, and pail or drum labels instructions for recommendations for each specific product. CURING COMPOUNDS GUIDE Curing Compounds