corner in each course. Table 8-4 lists the average
number of concrete masonry units by size and
approximate number of cubic feet of mortar required
for every 100 square feet of concrete masonry wall.
Table 8-5 lists the number of 16-inch blocks per
course for any wall.
You should always use outside measurements
when calculating the number of blocks required per
course. For example, a basement 22 feet by 32 feet
should require 79 blocks for one complete course.
Multiply 79 by the number of courses needed. Thus,
a one-course basement requires a total of 790 blocks
for a solid wall, from which deductions should be
made for windows and doors. If any dimension is an
odd number, use the nearest smaller size listed in the
For example, for a 22-foot by 31-foot
enclosure, use 22 feet by 30 feet and add one-half
block per row.
As a Builder, you might find yourself in the field
without the tables handy, so here is another method.
Use 3/4 times the length and 3/2 times the height for
figuring how many 8-by-8-by-16-inch blocks you
need for a wall. Lets take an example:
Given: A wall 20 ft long x 8 ft high
You can use rule 38 for calculating the raw
material needed to mix 1 yard of mortar without a
great deal of paperwork. This rule does not, however,
accurately calculate the required raw materials for
large masonry construction jobs. For larger jobs, use
the absolute volume or weight formula. In most
cases, though, and particularly in advanced base
construction, you can use rule 38 to quickly estimate
the quantities of the required raw materials.
Builders have found that it takes about 38 cubic
feet of raw materials to make 1 cubic yard of mortar.
In using rule 38 for calculating mortar, take the rule
number and divide it by the sum of the quantity
figures specified in the mix. For example, lets
assume that the building specifications call for a 1:3
mix for mortar, 1 + 3 = 4. Since 38 4 = 9 1/2, youll
need 9 1/2 sacks, or 9 1/2 cubic feet, of cement. To
calculate the amount of fine aggregate (sand), you
multiply 9 1/2 by 3. The product (28 1/2 cubic feet) is
the amount of sand you need to mix 1 cubic yard of
mortar using a 1:3 mix. The sum of the two required
quantities should always equal 38. This is how you
can check whether you are using the correct amounts.
In the above example, 9 1/2 sacks of cement plus
28 1/2 cubic feet of sand equal 38.
Figure 8-6.-Planning concrete masonry wall openings.