Masonry Magazine September 2008 Page. 36
COLORING
Although color is often blamed for efflorescence, pigments do not contribute to its formation.
To reduce the amount of cleaning required, clean deposits of colored mortar from the face of the masonry units during construction using a moist towel and stiff brush before the mortar cures and rigidly bonds to the masonry unit. Cleaning new masonry should be undertaken after the colored mortar has sufficiently cured (depending on weather conditions, generally seven to 14 days after the masonry installation). A commercially prepared "proprietary" masonry cleaner should be applied at manufacture's suggested dilution concentration. Cleaning too quickly and/or using muriatic acid or a highly concentrated masonry cleaner will caused degradation of the colored mortar with the consequential release of color pigments from their cement bond, and with the result of leaving a porous exposed sand surface. Insufficient or irregular washing can produce streaky or blotched areas on the masonry wall. For the well being of all involved, sample mock-up panels should be tested with job cleaning procedures and approved by the owner or architect.
Discoloration by efflorescence (a white coloration film of calcium and soluble salts) on the surface of the colored mortar joint is a common problem and more noticeable with colored mortar. Although color is often blamed for efflorescence, pigments do not contribute to the formation of efflorescence. To reduce the occurrence of efflorescence during construction, masonry walls should remain dry by covering with a strong waterproof tarp at the day's end. The design of the wall should include proper flashing to prevent penetration of wind-driven rains and allow weep holes for proper drainage. Masonry walls, which have moisture trapped, perpetuate the occurrence and reoccurrence of efflorescence.
The water-to-cement ratio of the mixed mortar will dictate the color shade of the mortar joint. A mortar mix with more water will lighten the color of the mortar joint, due to the pigment particles being spread farther with the extra water. Conversely, a mortar mix with less water will appear darker in color. Re-tempering of colored mortar with the addition of water should be avoided.
The rate of hydration affects the final shade of the mortar color. Cold weather masonry work has a slower cure cycle verses warmer masonry work. Therefore, jobs started at one time of the year and finished at another time can experience a difference in the final color, due to the change in the rate of hydration. During colder temperatures, the occurrence of efflorescence is more common due to the rate of hydration being slower.
The use of mortar color is not difficult, but it takes care and consistency to assure a uniform job. Fortunately, the masonry industry has experience using mortar color and for the most part, a job well done. Designers and specifiers must have realistic expectations concerning acceptable mortar color variations. When faced with a non-standard specified mortar color, rely on the expertise of pigment manufacturers and cement manufactures to assist with the match work and mix design. Rich Solomon is president of Solomon Colors Inc.
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