Hand Mixing

Where only small quantities of concrete are to be mixed or concrete work is to be done at rather infrequent intervals, it is usually more economical to do the mixing by hand. If any considerable quantity of concrete is to be mixed or the job is a large one, a batch machine mixer will be found more economical, will do away with the labor of hand mixing, and will insure greater uniformity of mixing.

Where concrete is to be hand mixed, a watertight mixing platform such as described elsewhere under the heading "Tools and Equipment," should be used. Hand mixing can be done on a smooth wood or concrete floor, but concrete never should be mixed on the ground, because soil will unavoidably be shoveled into the concrete and will reduce its strength if not spoil it entirely.

Size Of Batches

It is always best if possible to mix quantities or batches of concrete that will require the use of 1 sack of cement, because a sack of cement (94 lb. net) is considered as 1 cubic foot in proportioning concrete by volume, so the cement need not be measured. If, however, the work calls for smaller quantities, then it will be necessary to weigh out cement equal to 1/4, 1/2 or some other fractional part of a sack because when dumping it from the sack its fluffiness will deceive one as to its bulk.

Sand and cement mixed ready to receive the water. A measuring box also is shown.

Correspondingly small volumes of sand and pebbles must also be measured. Cement sacks should be carefully taken care of and not allowed to get wet, as they will be bought back by the dealer, if in good condition.

Order Of Mixing

In hand mixing, the required amount of sand should be measured first in the measuring box and spread out in a layer of uniform thickness on the mixing board. There should then be dumped on this sand the measured or weighed quantity of cement for the size of batch being mixed. Sand and cement should then be turned thoroughly a number of times, square pointed shovels being used for the purpose, until the two materials have been so thoroughly mixed that the mass is of uniform color throughout, free from streaks of gray or brown, indicating that the cement and sand have been thoroughly combined. This will usually require that the materials be thoroughly turned three or more times.

School boys mixing concrete preparatory to laying concrete sidewalk.

Next the required amount of pebbles or broken stone should be measured, thoroughly sprinkled, and added to the sand-cement mixture. One or two turnings should be given the materials while dry, after which water should be added, preferably from a watering pot with sprinkler attachment, or from hose with spray nozzle, water being added gently while some one turns the materials repeatedly to prevent the water from washing away the cement. The combined materials should be turned several times until every pebble or particle of broken stone is thoroughly covered with a sand-cement mortar and the whole mixture is of the required consistency. One should be very careful not to use too much water. Sometimes when it seems a little more water is necessary, it will be found that slightly more mixing will prove that the consistency is just right.

Two simple concrete flower or fern vases. The simplest ornament is here introduceddepressed panels.