SHOWING THE QUANTITIES OF MATERIALS AND THE RESULTING
AMOUNT OF CONCRETE FOR TWO-BAG BATCH.
Legend:
AA = Cement
BB = Sand
CC = Stone or Gravel
--------+-----------+-----------------------------------------------
|PROPORTIONS|
| BY PARTS. | TWO-BAG BATCH.
+---+---+---+-------------------+------+-------------+------
| | | | | | Size of |Water
| | | | | | Measuring | in
KIND OF | | | | Materials. | | Boxes. | Gal-
CONCRETE | | | | | | Inside | lons
MIXTURE.| | | | | |Measurements.| for
| | | +-----+------+------+ +------+------+Medium
| | | | | | | Con- | | |Wet
|AA |BB |CC | AA | BB | CC |crete.| BB | CC |Mix-
| | | | | | | | | |ture.
--------+---+---+---+-----+------+------+------+------+------+------
| | | |Bags.|Cu.ft.|Cu.ft.|Cu.ft.| | |Gal-
| | | | | | | | | |lons.
1:2:4 | 1 | 2 | 4 | 2 | 3¾ | 7½ | 8½ |2′×2′ | 2′×4′| 10
Concrete| | | | | | | | 11½″ | 11½″|
| | | | | | | | | |
1:2½:5 | 1 | 2½| 5 | 5 | 4¾ | 9½ | 10 |2′×2½′| 2′×5′| 12½
Concrete| | | | | | | | 11½″ | 11½″|
--------+---+---+---+-----+------+------+------+------+------+------
As above explained, concrete is composed of a certain amount of cement,
a larger amount of sand, and a still larger amount of stone (or
gravel). To determine how much of each of these materials to use, we
must first consider the type of work we wish to undertake. For ordinary
work about the farm (silos, tanks, cisterns, fence posts, well curbs,
etc., etc.) use twice as much stone as sand, and twice as much sand as
cement. This is called a 1: 2: 4 mixture—meaning that there are in
that mixture:
1 part of cement,
2 parts of sand,
4 parts of stone or gravel.
For sidewalks, gutters, etc., a “weaker” mixture is sometimes used,
consisting of:
1 part of cement,
2½ parts of sand,
5 parts of stone or gravel.
The proportions should always be measured by volume, and the best way
to do the measuring is by the use of a home-made “measuring box,”
of any kind of rough boards having straight sides, but with no top
or bottom. The size of these measuring boxes is determined by the
proportion desired for your mixture. For such boxes you need the
following sized lumber:
4 pieces 1 inch by 11½ inches by 2 feet rough (ends of sand and
stone boxes).
2 pieces 1 inch by 11½ inches by 4 feet rough (sides of sand box).
2 pieces 1 inch by 11½ inches by 6 feet rough (sides of stone box).
Note: The two pieces 4 feet long and the two pieces 6 feet long have an
extra foot in length at each end to be made into a handle, as shown in
Fig. 3.
For a 1: 2½: 5 mixture, you require the following sized lumber:
4 pieces 1 inch by 11½ inches by 2 feet (ends of sand and stone
boxes).
2 pieces 1 inch by 11½ inches by 4 feet 6 inches (sides of sand
box).
2 pieces 1 inch by 11½ inches by 7 feet (sides of stone box).
Note: The two pieces 4 feet 6 inches long and the
two pieces 7 feet long have an extra foot in length
at each end to be made into a handle, as shown in Fig. 3.
To illustrate the use of the measuring box, let us once more assume
that a 1: 2: 4 mixture is required, and that the amount of finished
concrete needed is 8½ cubic feet. By referring to the table on page
11 it will be noted that two bags of cement are required, also 3¾
cubic feet of sand and 7½ cubic feet of stone or gravel. Under “size
of measuring box” it is found that the sand should just fill a box 2
feet by 2 feet by 11½ inches, and that the stone should fill a box 2
feet by 4 feet by 11½ inches. Lay the sand box, or frame, on the mixing
platform and fill it. Then raise the box. Empty two bags of cement on
the sand and mix as described under “Mixing,” see pages 14-22. Even off
the mixture thus obtained with your shovel, place the stone measuring
box on top of the mixture and fill it. Raise the measuring box—and you
have the correct amount of stone all ready to be mixed with the cement
and sand. It is important to measure both the sand and stone _loose_ in
the box—never “pack” them.
For purposes of explanation, size of mixture will be referred to as
a “_batch_” of so many bags of cement. Thus, a “two-bag batch of
concrete” would mean one requiring two bags of cement, with the sand
and stone proportioned accordingly, as shown above.
For a “four-bag batch of concrete” it would be necessary to multiply
the amount of stone and gravel by 2, also multiplying the cubic
contents of the measuring box by 2, and using four bags of cement
instead of two.
The table previously referred to also shows the amount of water for
different sized batches, but it is to be noted that the quantity of
this ingredient is only approximated. Use the amount indicated in
the table for the first batch, and if it proves too wet for the use
desired, reduce the amount of water; if too dry, increase the amount of
water. Always use a bucket in measuring the amount of water, as this
secures uniform results.