Page 119 - Masonry and Concrete

Understanding Masonry
118 CHAPTER FOUR

use in masonry mortar and grout, sand must be clean, sound, and well
graded with a variety of particle sizes.
The sand in masonry mortar and grout acts as a filler. The cemen-
titious paste must completely coat each particle to lubricate the mix.
Sands that have a high percentage of large grains produce voids
between the particles and will make harsh mortars with poor worka-
bility and low resistance to moisture penetration. When the sand is
well proportioned of both fine and coarse grains, the smaller grains
fill these voids and produce mortars that are more workable and plas-
tic. If the percentage of fine particles is too high, more cement is
required to coat the particles thoroughly, more mixing water is
required to produce good workability, and the mortar will be weaker,
more porous, and subject to greater volume shrinkage. Figure 4-22
illustrates the range and distribution of particle gradation that is rec-
ommended, from the coarsest allowable gradation to the finest allow-
able gradation, with the ideal gradation shown in the middle. Both
the coarse and fine gradations have a void content much higher than

COARSE SAND IDEAL SAND FINE SAND

THE LEVEL OF LIQUID IN THE CYLINDERS, REPRESENTING VOIDS IN THE SAND
MIXTURE, IS LESS FOR A SAND HAVING THE IDEAL BLEND OF FINE AND
COARSE MATERIAL.
FIGURE 4-22
Sand particle gradation. (from Portland Cement Association, Trowel Tips—Mortar Sand).

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