Page 153 - Masonry and Concrete

Masonry Construction Techniques
152 CHAPTER FIVE

There are two traditional methods of mixing mortar on the job site.
For small projects, hand mixing is most economical, using a mason’s
hoe and a mortar box or wheelbarrow. First, all of the dry ingredients
are measured and mixed thoroughly with the hoe. Putting in half the
sand first, then the cement and lime, and then the rest of the sand,
makes blending a little quicker and easier. The materials are alter-
nately pulled and pushed back and forth until the color is even. The
mix is next pushed to one end of the mortar box or wheelbarrow, or a
hole is made in the middle, and one or two gallons of water added to
start. With a chopping motion of the hoe, the dry ingredients are
mixed into the water, and the mix alternately pushed and pulled back
and forth and more water added if necessary until the consistency and
workability are judged to be satisfactory.
For larger projects, machine mixing is used to combine mortar
ingredients. The mechanical drum or paddle-blade mixers used are
similar to but of lighter duty than concrete mixers because they are not
required to handle large-size aggregate. Capacities range from 4 to 7 cu.
ft. About three-fourths of the mixing water, half the sand, and all of the
cementitious ingredients are added first and briefly mixed together.
The balance of the sand is then added, together with the remaining
water. After all the materials and water have been combined, grout
should be mixed a minimum of five minutes, and mortar a minimum
of three and a maximum of five minutes. Less mixing time may cause
nonuniformity, poor workability, low water retention, and lower-than-
optimum air content. Overmixing causes segregation of materials and
entrapment of excessive air, which may reduce bond strength. Pig-
ments and admixtures are charged into the mixer last.

5.4 Unit Masonry Construction

Unit masonry construction consists of the placement of brick or block
and mortar and the installation of accessory items such as anchors,
ties, reinforcement, flashing, and weeps. The mechanics of brick and
block laying are not difficult to learn, but skill and speed will improve
only with time and practice. Increasing skill with trowel and mortar
makes the work go faster and more efficiently and increases daily pro-
duction rates. A skilled mason can lay an average of 530 modular brick
or 125 heavyweight concrete block or 160 lightweight block in a day.

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