Masonry Magazine May 2003 Page. 21
building owners gets professional results well ahead of a normal
schedule
projects that generally take three months can be done in three weeks-all with the look of classic mortared masonry, such as full raked joints on stacking. AZAR Dry-Stack can be placed with two hands, eliminating the need to lift conventional block with one hand and placing mortar with the other. Skilled workers are needed (but not as many are required on the crew) to ensure that the first course is level and plumb, that transitions at doors and windows are done correctly, and general supervision as the walls are built-out."
Ferguson makes a quick note on below grade applications of the mortarless/dry-stack systems. "We participate in the NCMA (National Concrete Masonry Association), specifically in the Basement Sub-Committee where the CMU/block producers have been complaining of losing market share to the poured/cast-in-place (CIP) systems in recent years-millions of units in the last year alone. Dry-stack methods offer the best hope of these producers to stem the tide of competition from CIP and pre-cast basement wall systems."
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.
Pigments made of carbon black have a high tint strength value and are listed under ASTM-C979, but are generally not accepted by manufacturers who supply pigments to the masonry industry. Exterior masonry mortars colored with carbon black have a history of losing color from the surface of the mortar joint within six months after installation. While carbon black itself is sun-fast, carbon black does not bond well to cement. It eventually disappears through weather exposure, resulting in a gradual loss of color on the surface area of the mortar joint.
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 a minimum of one percent color based on the total amount of cementitious material-to minimize the potential for color variations. Normally the amount of color used in a mortar mix falls between one percent and seven percent of the cementitious material weight. Generally, the seven percent dosage rate is the color saturation point; additional color added will not noticeably improve the intensity of the mortar color shade.
Masonry Procedures
As with all variables listed, mason contractors have a direct impact coward the colored mortar appearance of the structure. Mortar joints should always be tooled only after the mortar joint has achieved a "thumb print" consistency. Tooling the joints too soon brings excessive noisture from the mortar to the surface and creates a masonry smear wighter in color. Conversely, tooling a mortar joint that has become too ry tends to burn or scrape the joint due to lack of moisture. The result s a mortar joint darker in color.
To reduce the amount of cleaning required, clean deposits of colored nortar from the face of the masonry units during construction using a noist towel and stiff brush before the mortar has a chance to cure and igidly bond itself to the masonry unit.
Cleaning of new masonry should be undertaken after the colored nortar has sufficiently cured (depending on weather conditions, generally up to 14 days after the masonry installation). A commercially pre-pared "proprietary masonry cleaner should be applied at nanufacturer'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. The result will be the leaving of a porous exposed sand surface.
Insufficient or irregular washing can produce streaky or blotchy areas on the masonry wall. For the well being of all involved, sample mock-up panels should be constructed and 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 mortar joint is a common problem and tends to be 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, the masonry walls should be kept dry by covering with a strong waterproof tarp at the end of each day. 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 that 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 far ther with the extra water. Conversely, a mortar mix with less water will appear darker in color. Retempering 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 of year 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 terribly difficult, but it takes some care and consistency to assure a uniform job. 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, president of Solomon Colors, a leading producer of mortar colors to the masonry industry. Rich Solomon can be reached at rsolomon@solomoncolors.com or by phone using (800) 624-0261.
May 2003
Masonry 19