Masonry Magazine September 2008 Page. 34
COLORING
The more cement in the mix, the darker the mortar.
Mortar mix design
THE ASTM C270 SPECIFICATION for Mortar Unit Masonry includes Prepared Masonry (ASTM C91) Type N,S,& M Masonry Cement and Type O,N,S, & M Portland Cement (ASTM C150) Lime (ASTM C207) Mortars plus Sand (ASTM C144) used in each mix design. As with the shade of cement affecting the mortar color, the type O, N, S, & M strength mortars and sand shade will also influence the colored mortar shade. The cement to lime ratio will determine the lightness of the mortar. The more cement in the mix the darker the mortar. Thus, type M strength mortar will be the darkest, type S second darkest, type N third darkest, and type O lightest with the highest concentration of lime. With more Type S mortars being specified, the ability to produce lighter colored mortar joints such as buffs, tans and pink shades are becoming more difficult without utilizing white cement or a light gray portland cement. As with cement, the shade of sand will change the shade of colored mortar. Light-colored sand will allow a brighter more intense color. Conversely, darker sand will mute the color shade. Sand with more fines will also mute the color shade due to the increased surface area the pigment is required to coat with pigment particles.
GOOD TO KNOW
The following criteria should be considered when specifyin and producing a particular mortar shade:
• Cement shade
• Mortar mix design
• Color pigments
• Masonry procedures
Color pigments
A STABLE, HIGH-QUALITY PIGMENT should be utilized to assure a long-lasting mortar color shade. Color pigments with a proven history of longevity in masonry are made from natural and synthetic iron oxides (red, black and yellow), Cobalt (blue), titanium oxide (white) and Chromium oxide (green). Blends of the red, black and yellow natural and synthetic iron oxides will produce buffs, browns, tans, coppers, oranges, chocolates and other colors needed to compliment the vast colors found in brick, block and stone. These pigments exceed the requirements set forth by ASTM-C979 "Pigments for Integrally Colored Concrete." The pigments are water-wetable, lightfast, alkali resistant, stable under curing, and will not adversely affect the strength of cement when added at less than 10 percent of the weight of cementitious ingredients.
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32 Masonry
September 2008 www.masoncontractors.org
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