Page 120 - Masonry and Concrete

Understanding Masonry
119
UNDERSTANDING MASONRY

that of the ideal gradation and will affect the amount of cement
required to produce good mortar.
Sand particles should always be washed to remove foreign sub-
stances. Silt can cause mortar to stick to the trowel and can impair
proper bond of the cementitious material to the sand particles. Clay
and organic substances reduce mortar strength and can cause brown-
ish stains varying in intensity from batch to batch. There is a simple
field test which can determine the amount of contaminants in
masonry sand. Put 2 inches of sand in a quart jar, add water until the
3
jar is about 4 full, shake it for 1 minute, then let it stand for an hour.
1
If more than 8 in. of sediment settles on top of the sand, it should be
washed by drenching with a garden hose the day before it will be used
(see Figure 2-9 in Chapter 2).
Masonry mortar is used to fill relatively small joints between units,
so sand is the largest practical aggregate that can be used. But masonry
grout is used to fill larger cores and cavities in masonry construction,
so it is both practical and economical to include larger aggregate in
addition to sand. Maximum aggregate size for masonry grout is usually
3
limited to 8 inch so that the grout can still flow easily into unit cores
and wall cavities even when they are crowded with reinforcing bars.

4.6.4 Mixing Water

Water for masonry mortar must be clean and free of harmful amounts
of acids, alkalis, and organic materials. Whether the water is drinkable
is not in itself a consideration, as some drinking water contains appre-
ciable amounts of soluble salts, such as sodium and potassium sulfate,
which can contribute to efflorescence. In general, though, water that is
drinkable, is reasonably clear, and does not have a foul odor or a brack-
ish or salty taste is acceptable for mixing masonry mortar and grout.

4.6.5 Mortar and Grout Admixtures
Although admixtures are often used with some success in concrete
construction, they can have adverse effects on the properties and per-
formance of masonry mortar and grout. Masonry industry standards
do not incorporate, nor in fact even recognize, admixtures of any kind.
A variety of proprietary materials are available which are reported by
their manufacturers to increase workability or water retentivity, lower
the freezing point, and accelerate or retard the set. Although they may

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