Part 2

The presence of dirt in the sand is easily ascertained by rubbing a little in the palm of the hand. If a little is emptied into a pail of water, the presence of dirt will be shown by the discoloration of the water. This can be discovered also by filling a fruit jar to the depth of 4 inches with sand and then adding water until it is within an inch of the top. After the jar has been well shaken, the contents should be allowed to settle for a couple of hours. The sand will sink to the bottom, but the mud, which can be easily recognized by its color, will form a distinct layer on top of the sand, and above both will be a clear depth of water. If the layer of mud is more than one-half inch in thickness, the sand should not be used unless it is first washed.

Having discovered that the sand you contemplate using is not clean, and provided you cannot readily obtain any that _is_ clean, you may use what you have, provided you wash it in the following manner:—

Build a loose board platform from 10 to 15 feet long, with one end a foot higher than the other. On the lower end and on the sides, nail a board 2 by 6 inches on edge, to hold the sand. Spread the sand over this platform in a layer three or four inches thick, and wash it with a hose. The washing should be started at the high end, and the water allowed to run through the sand and over the 2 by 6-inch piece at the bottom. A _small_ quantity of clay or loam does not injure the sand, but any amount over 5 per cent. does.

Stone or Gravel

This is known as the “coarse aggregate” of concrete. Great care should be used in its selection. The pebbles should be closely inspected to see that there is no clay on their surface. A layer of such clay prevents the “binding” of the cement. If necessary stone or gravel may be washed in the same way as above described for sand. Indeed, it is more easily done than sand, as the water flows through the larger voids in the gravel more readily than through the voids in the sand. Dust may be left in the crushed stone without fear of its interfering with the strength of the cement, but care should be taken to see that such dust is distributed evenly through the whole mass, and when dust is found in stone, slightly less sand should be used than ordinarily.

As to the size of stone or gravel, this must be determined by the form of construction contemplated. For foundations or any large thick structure, use anything from ½ to 2½ inches in diameter. For thin walls use ¼ to 1-inch stone.

The best results are obtained by the use of a mixture of sizes graded from small to large. By this means the spaces or voids between the stones or pebbles are reduced and a more compact concrete is obtained. Moreover, this method makes it possible to get along with less sand and less cement.

Pure Water Necessary in Mixing

Water for concrete should be clean and free from strong acids and alkalies. It may be readily stored in a barrel beside the mixing board and placed on the concrete with a bucket. If you are at all in doubt about the purity of the water that you contemplate using, it would be well to make up a block of concrete as a test, and see whether the cement “sets” properly.

Proportioning the Mixture

That mixture in which all the spaces (called “voids”) between the stone or gravel are filled with sand, and all the spaces between the sand are filled with cement, is the ideal mixture. This mixture is rarely attained, as the voids in each load of gravel and sand vary slightly, and in order to be absolutely safe, it is well to use a little more cement than will just fill the voids.

TABLE I.

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.

Natural Mixture of Bank Sand and Gravel

Naturally mixed bank sand and gravel are sometimes found in the right proportions for making concrete. Generally, however, there is far too much sand for the gravel, and great care should be exercised in using this class of material. Unless the mixture runs very even throughout the bank, and is found to be made up of one part sand to two parts gravel, it is better to screen the sand out of the gravel and prepare the materials in the usual way.

Herewith is a table showing the quantities for a natural mixture of bank sand and gravel. The quantities can be found in the same way as in Table I, on page 11.

TABLE II.

SHOWING THE QUANTITIES OF MATERIALS AND THE RESULTING AMOUNT OF CONCRETE FOR TWO-BAG BATCH, USING NATURAL MIXTURE OF BANK SAND AND GRAVEL.

+---------------+------------------------------------------- | PROPORTIONS | TWO-BAG BATCH FOR NATURAL MIXTURE OF | BY PARTS. | BANK SAND AND GRAVEL. +-------+-------+---------------+-------+----------+-------- | | | | | Size of | | | | Materials. | |Measuring | KIND OF | | | | | Boxes. | CONCRETE| | +-------+-------+ +----------+Water in MIXTURE.| |Natural| |Natural| Con- | |Gallons |Cement.|Mixture|Cement.|Mixture|crete. |Mixture of| for | |of Sand| |of Sand| | Sand and |Medium | | and | | and | | Gravel. |Wet | |Gravel.| |Gravel.| | |Mixture. --------+-------+-------+-------+-------+-------+----------+-------- | | | Bags. |Cu. ft.|Cu. ft.| |Gallons 1:2:4 | 1 | 4 | 2 | 7½ | 8½ |2′×4′×11½″| 10 Concrete| | | | | | | | | | | | | | 1:2½:5 | 1 | 5 | 2 | 9½ | 10 |2′×5′×11½″| 12½ Concrete| | | | | | | --------+-------+-------+-------+-------+-------+----------+--------

There are three kinds of mixtures, in general, on concrete work:—

1st.—_Very Wet Mixture._—Concrete wet enough to be mushy and run off the shovel when handling, used for thin walls or for thin sections, etc.

2d.—_Medium Mixture._—Concrete just wet enough to make it jelly-like, used for foundations, floors, etc. To better describe this mixture it may be said that a man should sink ankle deep if he were to step on top of the pile.

3d.—_Dry Mixture._—Concrete like damp earth, used for foundations, etc., where it is important to have the concrete “set” up as quickly as possible.

The difference between the mixtures is, that the dryer the mixture the quicker will the concrete “set up”—but in the long run, when carefully mixed and “placed,” the results from any of the above mixtures will be identical. It may be said, however, that a dry mixture is the harder to handle, must be protected with greater care from the sun or from drying too quickly; and lastly, is likely—unless used by most experienced hands—to show voids or stone pockets in the face of the work when the “Forms” are removed. The less the voids in the stone or gravel, the greater will be the volume of the concrete. In general, the amount of concrete will be greater in each instance than is shown in the table—especially when gravel is used.

Tools

One great advantage of concrete, so far as the farmer is concerned, lies in the fact that, generally speaking, it necessitates no outlay for tools, for it so happens that most of the tools needed for forms of concrete construction are the very ones every farmer uses—

Shovels—One for each man on the job.

Wheelbarrows—At least two, preferably those with sheet iron bodies.

Rake.

Water Barrel.

Several Water Buckets.

A Tamper or Rammer—This is made of wood with handles nailed to it, as shown in Fig. 2. The measurement is 4 inches by 2 inches by 2 feet 6 inches.

A Garden Spade.

A Sand Screen, made by nailing a piece of ¼-inch mesh wire screen, 2½ feet by 5 feet in size, to a frame made of 2-inch by 4-inch scantling.

In addition to the above tools you will require a Mixing Board. This is simply a water-tight platform. It should be (for a two batch mixture and for two men to work on) about 10 feet square. Make it out of 1-inch boards 10 feet long, surfaced on one side, using 5 cleats to hold the boards together. The cleats should measure 2 inches by 4 inches by 9 feet. If 1-inch by 6-inch tongued and grooved roofers can be obtained, these will answer very nicely, provided they are fairly free from knots. The object of having surfaced boards is to make the shoveling or turning easy. The boards should be so laid as to enable the shoveling to be done with and not against the cracks between the boards. The boards must be drawn up close in nailing, so that no cement “grout” will run through while mixing.

For a larger job, a slightly larger mixing board will be needed.

In setting up your mixing board, choose a place giving plenty of room near the storage piles of sand and stone. Block up your concrete board level, so that the cement grout will not run off on one side, and so that the board will not sag in the middle under the weight of the concrete.

Wheelbarrow “Runs”

You will also have to make wheelbarrow “runs” leading from your mixing board to the spot where the concrete is to be placed. Do not use, for these runs, any old boards that are handy. Make a good run—smooth, and, if much above the ground, at least 20 inches wide. This one feature will lighten and quicken the work to a remarkable extent.

How to Mix Concrete

Having selected the proper materials and arranged the mixing board and runs, the next step is the actual process of mixing.

The proportions of materials and the nature of same for various types of work have already been described on pages 11-13. In following the mixing instructions here given, considerable assistance will be obtained by referring to the illustrations with which instructions are interspersed.

The Hand Mixing Method

There are many ways of “hand mixing,” all having the same good results. The way described here we believe to be the one best calculated to obtain good results with a minimum of labor. In this description, and the accompanying illustrations, we have taken as a basis a “Two-Bag Batch” of 1: 2: 4 concrete.

First load your sand in wheelbarrows from the sand pile, wheel on to the “Board,” and fill the sand measuring box, which is placed about two feet from one of the 10-foot sides of the board, as shown by the diagram in Fig. 3. When the sand box is filled, lift it off and spread the sand over the board in a layer 3 or 4 inches thick, as shown in Fig. 4. Take the two bags of cement and place the contents as evenly as possible over the sand (see Fig. 4). With the two men at points marked “x” and “xx” on the sketch below Fig. 4, start mixing the sand and cement, each man turning over the half on his side of the line AA. Starting at his feet and shoveling away from him, each man takes a full shovel load, turning the shovel over at the points marked 1 and 2 respectively in Fig. 4. In turning the shovel, do not simply dump the sand and cement at the points marked 1 and 2 in the diagram under the cut, but shake the materials off the end and sides of the shovel, so that the sand and cement are mixed as they fall. This is a great assistance in mixing these materials. In this way the material is shoveled from one side of the board to the other, as shown in Figs. 5 and 6. Fig. 5 shows the first turning, and Fig. 6 the second turning.

The sand and cement should now be well mixed and ready for the stone and water. After the last turning, spread the sand and cement out carefully, place the gravel or stone measuring box beside it as shown in Fig. 7, and fill from the gravel pile. Lift off the box and shovel the gravel on top of the sand and cement, spreading it as evenly as possible. With some experience, equally good results can be obtained by placing the gravel measuring box on top of the carefully leveled sand and cement mixture, and filling it, thus placing the gravel on top without an extra shoveling. This method is shown in Fig. 8. Add about three-fourths the required amount of water, using a bucket and dashing the water over the gravel on top of the pile as evenly as possible. (See Fig. 9). Be careful not to let too much water get near the edges of the pile, as it will run off, taking some cement with it. This caution, however, does not apply to a properly constructed mixing board, as the cement and water cannot get away. Starting the same as with the sand and cement, turn the materials over in much the same way, except that instead of shaking the materials off the end of the shovel, the whole shovel load is dumped as at points 1 or 2 in the diagram under Fig. 4 and dragged back toward the mixer with the square point of the shovel. This mixes the gravel with the sand and cement, the wet gravel picking up the sand and cement as it rolls over when dragged back by the shovel. (See Fig. 10). Add water to the dry spots as the mixing goes on until all the required water has been used. Turn the mass bade again, as was done with the sand and cement. With experienced laborers, the concrete should be well mixed after three such turnings; but if it shows streaky or dry spots, it must be turned again. After the final turning, shovel into a compact pile. The concrete is now ready for placing.

Mixing Natural Mixture of Bank Sand and Gravel

Spread out the mixture of sand and gravel as much as the board will readily permit, add enough water to wet the gravel and sand thoroughly, spread the cement evenly in a thin layer over the sand and gravel, and turn over, as described previously, at least three times, adding the rest of the water necessary to get the required consistency while the materials are being turned. It requires some experience to work up a natural mixture of bank sand and gravel, and if at all doubtful about the concrete made from it, first screen the sand from the gravel, and then mix in the regular way.

Number of Men

For the above operation only two men are required, although more can be used to advantage. If three men are available, let two of them mix as described above and the third man supply the water, help mix the concrete by raking over the dry or unmixed spots as the two mixers turn the concrete, help load the wheelbarrows with sand and stone or gravel, etc. Fig. 5 shows a third man on the board. In this illustration, he is helping mix the sand and cement by raking it—a most effective practice.

If four men are available, it is best to increase the size of the batch mixed to a four-bag batch, doubling the quantities of all materials used. The cement board should also be increased to 10 by 12 feet as shown under “Tools.” In this case start the mixing in the middle of the board, and each pair of men mixing exactly as if for a two-bag batch, except that the concrete is shoveled into one big mass each time it is turned back on to the center of the board. When more than four men are available, the rest may place the concrete, make new runs, load wheelbarrows, etc., taking the concrete away from the board as fast as it is mixed. In this case another small concrete board should be placed next to the big “board,” so that in the last turning the batch can be shoveled over on to the small board for placing, making room on the big board to mix the next batch. The small platform need be only just big enough to hold the pile of mixed concrete.

How to Determine Quantities of Materials Needed

First figure the number of cubic feet of concrete that will be required for the work in question. Then by multiplying this number by the number under the proper column and required mixture shown in Table III, the amounts of cement, sand, and stone or gravel can be found.

TABLE III.

+------------------------------------------------ | QUANTITIES OF MATERIAL IN 1 CU. FT. OF CONCRETE +---------+--------------+----------------------- MIXTURE | Cement, | Sand, | Stone or Gravel, | Barrel | Cu. Yard | Cu. Yard -------------------+---------+--------------+----------------------- 1 : 2 : 4 Concrete| .058 | .0163 | .0326 1 : 2½ : 5 Concrete| .048 | .0176 | .0352 -------------------+---------+--------------+-----------------------

=Example=

Suppose the work consists of a concrete silo requiring in all 935 cubic feet of concrete, of which 750 cubic feet is to be 1: 2: 4 concrete, and 185 cubic feet is to be 1: 2½: 5 concrete. Also enough sand and cement is needed to paint the silo inside and outside, in all 400 square yards of surface, with a 1: 1 mixture of sand and cement. One cubic foot of 1: 1 mortar will paint about 15 square yards of surface and requires 0.1856 barrels of cement and 0.0263 cubic yards of sand.

=Solution, Etc.=

Thus the necessary quantities of materials are:—

57½ barrels of Portland cement. 16½ cubic yards of sand. 31 cubic yards of stone or gravel.