Change any ingredient or step in the manufacturing process and the color of colored concrete masonry units changes too. The same is true for colored mortar. Change the pigment, cement, sand, amount of water, batching sequence, or curing conditions, and mortar color also changes. To achieve a finished wall that is uniform in color, the block producer and masonry contractor must closely control all these factors from batch to batch. If they don't, the color of the block or mortar changes and the finished wall ends up with off-color splotches. PIGMENT The ingredient that affects color the most is the color pigment itself. ASTM C 979 identifies four types of color pigments for concrete: synthetic and natural iron oxides, chromium oxide green, cobalt blue, and carbon black (concrete grade). CEMENT Cement color also influences the color of concrete block and mortar. In general, the lighter the cement color, the brighter and cleaner the concrete or mortar color. AGGREGATE, WATER, AND ADMIXTURES Because the greatest portion of a concrete mix is aggregate, the color or gradation of aggregate can influence the color of concrete or mortar a lot. The amount of water in the mix influences color a lot too. The higher the water-cement ratio, the lighter the color that results. Water reducers, integral water repellents, and other admixtures also can affect the color of units and mortar. BATCHING, MIXING, AND CURING To produce a uniform color, the block producer and masonry contractor must measure and batch all ingredients accurately and consistently from batch to batch.