Page 122 - Masonry and Concrete

Understanding Masonry
121
UNDERSTANDING MASONRY

also produce brighter, cleaner colors than natural iron oxides. Beyond
a certain point, called the saturation point, the color intensity of the
mortar does not increase in proportion to the amount of pigment
added. Synthetic iron oxides generally are saturated at about 5% of the
weight of the cement, and natural oxides at about 10%. Adding pig-
ment beyond the saturation point produces little additional color.
Colored mortar can be made at the job site from powdered or liquid
pigments. Powdered pigments are used most frequently, and the
majority are packaged so that one bag contains enough pigment to
color one cubic foot of cementitious material (i.e., for each one-cubic-
foot bag of masonry cement, portland cement, or lime, one bag of color
is added). Pigment manufacturers supply charts which identify the
exact number of bags of pigment required for various mortar propor-
tions. Similarly, liquid colorants are generally packaged so that one
quart of pigment is needed for each bag of cementitious material. Liq-
uid pigments create less mess and blowing dust than dry powders, but
they also cost more. The same pigments used to color mortars are used
to produce colored concrete masonry units. Some manufacturers mar-
ket colored masonry cements, mortar cements, and prebagged port-
land lime mortar mixes in which pigments are preblended in the bag
with the other ingredients. These will generally produce mortar colors
that range from white, cream, buff, tan, and pink to chocolate brown.
This is the easiest way to get colored mortar.
Shrinkage-compensating admixtures (commonly called grouting
aids) are often used in grout which typically shrinks 5–10% after
placement as the surrounding masonry units absorb water. To mini-
mize volume loss, maintain good bond, and give workers more time to
vibrate the grout before it stiffens, these specially blended admixtures
expand the grout, retard its set, and lower the water requirements.
Admixtures can also be used to accelerate grout set in cold weather or
retard set in hot weather. Superplasticizers may be used in hot weather
to increase grout slump without adding water or reducing strength.

4.6.6 Mortar and Grout Mixes
For years there has been controversy over the relative merits of mor-
tars made with portland cement and lime versus mortars made with
masonry cement. Historically, portland cement and lime mortars have
higher flexural bond strengths than masonry cement mortars. Higher

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