With colored mortar, you must keep everything consistent: the ingredients, the proportions, job conditions, and workmanship. SYNTHETIC OR NATURAL PIGMENT? Most mortar colorants are made from iron oxide pigments. Iron oxides are nontoxic, colorfast, chemically stable in mortar, and resistant to ultraviolet radiation. Iron oxide pigments are either natural or synthetic. Synthetic iron oxides have more tinting power: less pigment is needed to produce a certain amount of mortar color. They also can produce brighter, cleaner colors than the natural iron oxides. But synthetics cost almost 2 times as much as natural oxides. ADMIXTURE OR PRECOLORED, PREBAGGED MORTAR? Colored mortar can be made at the jobsite from powdered or liquid pigments or from precolored masonry cement or precolored, prebagged portland cement-lime. Precolored, prebagged mortars are somewhat simpler to use. MAKE A TEST PANEL Before finally deciding on a mortar color, architects should have a sample panel built using the specified materials and the expected jobsite practices. TOOLING COLORED JOINTS Tooling joints pushes the sand down and draws the cement paste to the surface, densifying the joint. Because this affects the color of the mortar, the joints must be tooled the same way and when the mortar is at the same consistency throughout the job. CLEANING IS CRITICAL According to one pigment manufacturer, more than 90% of colored mortar problems are caused by improper cleaning.