THE USE OF CEMENT.

King Country Chronicle, Volume VI, Issue 420, 6 December 1911, Page 6

THE USE OF CEMENT.

In selecting sand the first thing to consider is cleanliness. In testing this point it may be placed in the palm of one hand and rubbed with the fingers of the other hand. If the sand is dirty it will discolour the fingers and palm. If it is possible to select from several varieties, that; sand should be chosen which is composed of sharp angular grains, varying in size from coarse to line. tiuch sand is, however, not always obtainable, nor is it essential for good work. The voids in sand vary according to variation in the size of grains. That sand which contains many different, sizes of sands is preferred, because it takas less cement to fill the voids. It is not uncommon to alternate with a shovel of coarse sand and then a shovel of fine sand in order to reduce the size of the voids.

The sand and tne gravel or crushed rock taken together are usually spoken of as the aggregate. As with the sand, it is the best, to select a gravel or rock in which there are many sizes, as this economises cement. The best mixture which can be used for the creamery floor consists of one part cement, "three parts sand, and sixparts gravel or crushed rock, and is usually expressed a? follows:--], 3, 0. If a base is to be constructed for the engine or separator, it is best to use a mixture of 1, 2. 4, as this is much stronger and will better withstand the. vibration of the machinery. For outside walls the first mixture mentioned is very snitsfactory. On large jobs it is more economical to mix concrete by machine; but for small jobs, using even as much as several hundred yards of concrete, it is much cheaper and more expedient to mix by hand. Especially is this true when only two or three men are available te do the work and the work is often interrupted. Either "handmixing" or "machine-mixing" is perfectly satisfactory when it is carried on properly. In "hand-mixing" a piatiorm or shallow box of convenient size should bee onstructed. First deposit the requisite amount of sand in a uniform layer, and on top of this spread the cement. These should he mixed with shovels or hoes, until the whole mass exhibits a uniform colour. A great deal of concrete is spoiled in making by improperly mixing. It requires considerable muscle on the part of the man with the shovel. When the whole, mass exhibits a uniform colour a crater should be formed in the dry mixture, and into tfis is poured nearly the entire quantity of water required for the "batch." The dry material should always be worked from the outside towards the centre, and water can be added as desired until the proper consistency is obtained.