Masonry Magazine June 2001 Page. 35
Colored Mortar
Mortar color can have a dramatic effect on brick appearance. LEFT photo illustrates the difference between gray mortar and red mortar. MIDDLE photo illustrates the difference between gray mortar and tan mortar color. RIGHT photo illustrates the difference between gray mortar and maroon mortar color.
CEMENT SHADE
Masonry and Portland cement are produced with different manufacturing processes offering a variety of shades from light gray to dark gray color tones. The cement color shade will have a pronounced direct effect towards the mortar color. Adding color to light gray cements will produce brighter and cleaner color shades. Conversely, utilizing dark gray cement will limit your ability to produce light color shades such as buff or pink. If a light pastel color is specified, more than likely white cement must be used to obtain the desired mortar color. In the past few years there has been tight cement production levels with increased demand for cement, which in turn has created a shift towards darker shades of cement. To maintain uniformity throughout the job, visual inspections of each cement delivery should be compared against future shipments of cement. In addition, stay with the same cement manufacturer during the duration of the job. The use of the lightest shade of gray portland or masonry cement will enhance the vibrancy of the finished mortar color.
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 portland 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. Clean 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.
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 dioxide (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% of the weight of cementitious ingredients.
The pigments used to color mortar have a high tint strength value and are added to the mortar mix based on the weight of all cementitious materials in the mix (Portland Cement, Lime, or Masonry Cement). It's best to use no less than 1% color based on the total amount of cementitious material to minimize the potential for color varia-
Cement
Variations of cement from different manufacturers.
Sand
Pigment
Variations of sand from different sources.
Iron oxide - red, yellow, black.
MASONRY JUNE, 2001 35