ACI 524R-16 Guide to Portland Cement-Based Plaster

ACI 524R-16 Guide to Portland Cement-Based Plaster. 4.5—Water Potable water is generally acceptable to use as plaster mixing water. Water used in mixing and curing portland cement-based plaster should be clean and free from damaging amounts of deleterious materials such as oils. acids, alkalis, organic matter, or salts, Such substances may impair the setting or curing characteristics of the plaster. Certain minerals or metals can stain or discolor plaster when present in appreciable amounts. 4.6—Admixtures The following admixtures can be added when permitted by the project specifications. 4.6.1 A ir-entraining admixsures—Air-entraining admix- Lures that conform to ASTM C260/C260M reduce water demand. absorption, and water penetration while improving workability and resistance to freezing-and-thawing damage. Pretest combinations of cement binders and air-entraining admixtures, as certain air-entraining admixture combinations can have adverse behaviors. Do not substitute household-type soaps or detergents for appropriate air-entraining admixtures. 4.6.2 calcium chloride—Calcium chloride should conform to ASTM DQg. Calcium chloride is available in liquid. powder. tlake. and prill (pea-sized granule) form. Dis’ ke calcium chloride in flake or pt-ill form in water before adding it to the plaster mixture. Calcium chloride, or accelerating admixtures containing significant amounts of calcium chloride. can accelerate the corrosion rate of metals. Do not use calcium chloride when portland cement-based plaster will come into contact with metal lath, anodized aluminum. galvanized steel, or zinc accessory products. Prolonged embedment olmetal within a high-chloride plaster can cause corrosion expansion of the metal and cracking of the plaster. Noncorroive accelerating admixtures meeting ASTM C494C494M are recommended in situations where acceleration of set is desired, but corrosion to embedded metal is a risk. (.‘alcium chloride can also cause mottling to be more exaggerated (16.5). 4.6.3 JJter-reducing admLvtures—Water-reducing admixtures and certain plasticizers that conform to ASTM (‘494/ C494M can be used to reduce the water-cementitious material ratio (w/crn) of a portland cement-based plaster. Water- reducing admixiures can potentially increase strength. increase workability, and reduce shrinkage cracking. Observe manufacturer’s recommendations when using water reducers or plasticizers. Small changes in admixture quantities can have significant effects on the properties of portland cement-based plaster. 4.6.4 Iiaer-repellent admxsures—Stearate emulsions. not to exceed 2 percent by mass of cement. can be used to improve water repellency and decrease absorption of the hardened plaster. Some of these emulsions can also entrain air. Stearates can reduce bond between plaster coats. and stearates’ water-repellent elkcts can degrade with time.ACI 524R pdf download.