Page 150 - Masonry and Concrete

Masonry Construction Techniques
149
MASONRY CONSTRUCTION TECHNIQUES

functions, it must be properly mixed and placed to achieve intimate
contact with the unit surface and form both a mechanical and chemi-
cal interlock.
Mortar mixes must be carefully controlled at the job site to main-
tain consistency in performance and appearance. Consistent measure-
ment of mortar ingredients should ensure uniformity of proportions,
yields, strengths, workability, and mortar color from batch to batch.
Volume rather than weight proportioning
is most often used because it is simpler.
Proportions by Volume
Ingredient proportions for the various
types of conventional mixes are shown in Mortar Type Portland Cement Lime Sand
Figures 5-12 and 5-13. Portland cement, 1 1
M 1 ⁄4 3- ⁄2
mason’s lime, and masonry cement are 1 1
S 1 ⁄2 4- ⁄2
packaged and labeled only by weight.
N 1 1 6
Each bag of portland cement or masonry O 1 2 9
cement equals one cu. ft. regardless of its K 1 3 12
labeled weight, and each bag of hydrated
1
mason’s lime equals 1- 4 cu. ft. regardless FIGURE 5-12
of its weight. Cement and lime are gener- Proportions for portland cement and lime mortars.
ally charged into the mixer in whole or (from ASTM C270 Standard Specification for Mortar
half bags, depending on the mixer size and for Unit Masonry, American Society for Testing and
Materials, West Conshohocken, PA).
the batch size needed.
Volume measurements of sand are
often miscalculated because of variations
in the moisture content of the sand. Com- Proportions by Volume
mon practice is to use a shovel as the stan- Masonry Cement
dard measuring tool for sand, but moisture or
in the sand causes a bulking effect. Wet Mortar Cement
sand occupies more volume than the same
Mortar Type M S N Sand
weight of dry sand. This often causes over-
or undersanding of the mix, which affects M 1 3
both the strength and bonding characteris- S 1 3
N 1 3
tics of the mortar. Oversanded mortar is
harsh and unworkable, provides a weak
FIGURE 5-13
bond with the masonry units, and per-
Proportions for masonry cement and mortar cement
forms poorly in freeze-thaw conditions.
mortars. (from ASTM C270 Standard Specification for
The simplest method of consistently mea- Mortar for Unit Masonry, American Society for Testing
suring and batching sand by volume is by and Materials, West Conshohocken, PA).

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