Special Types Of Concrete For Use On Farms

Bay of Plenty Beacon, Volume 13, Issue 6, 11 October 1948, Page 3

Special Types Of Concrete For Use On Farms

Special concretes which are often suitable for jobs on the farm are described in the following extracts from an article by A. W. Riddolls, senior lecturer in agricultural engineering at Lincoln College.

Dry mix concrete is a method of making concrete building blocks, fence posts, and similar precast jobs, so that they can be turned out of the forms or moulds immediately. The concrete is mixed very dry, and rammed or heavily vibrated very tightly into the mould. The mould is then removed, and the concrete, if sufficiently dry, stands up by itself, just like the moist sand is turned out on a bucket by a child at the beach. ’ The concrete, having insufficient mixing water, is considerably weaker when hardened - than ordinary wet mix concrete, but quite strong enough for reinforced fence pests and building blocks.. For building blocks a 1 cement, -2 sand, 6 gravel mix has been found very satisfactory, using gravel screened through a §” mesh sieve. It gives an attractive surface finish, and as it does not contain much sand it does not absorb moisture readily. Sand concrete, composed of 1 cement, 5 sand, is also used. The surface of the block is very smooth, but it absorbs moisture readily. For fence posts, dry mix is commonly 1 cement, 2 sand, 3 gravel. Ordinary vibrators are not of much use for dry mix, but special vibrators giving a very heavy jolting action have been- used satisfactorily. It is most important to compact the concrete thoroughly in the mould, either by thorough ramming of by heavy vibration. Sawdust Concrete On account of its good heat insulating properties, concrete made of sawdust and cement has been used successfully for such work as piggery floors land walls. Common mixes: are 1 cement, 4 sawdust for walls, and 1 cement, 2 sawdust for floors, but it would be necessary to experiment on a small scale with any particular sawdust before carrying out a large job,-as failures have occurred with sawdust concrete. Sawdust of soft woods such as pinus radiata has been found most, satisfactory. Soil-Cement Concrete

Concrete made from * soil and cement has been used for many years in U.S.A. for air strips, roads and paths. The soil should be somewhat sandy and fairly low in humus and should not contain more than ab'out 20 per cent of clay. This method of construction is still experimental, and trials with different soils and mixes would be desirable before attempting large-scale work. Building blocks could be constructed of similar material. Light Aggregate Concrete Concretes composed of cement with cinders, pumice, scoria and similar materials are light, and have good heat insulating properties, although the concrete is not as strong as ordinary concrete. It is used for buildings to house stock such as piggeries. The usual mix is 1 part cement to 4i parts light aggregate. Walls and floors of these materials are much warmer than those of ordinary concrete. A chemical product recently developed overseas, when included with the mix, aerates concrete and makes it much lighter, besides giving it good heat insulating properties. Walls of buildings made of ordinary concrete are inclined to allow dampness from rain to pass through the wall by capillary action. It has been found that if the sand is omitted from the concrete mix, capillary action does not occur, and the walls keep drier and warmer than with ordinary concrete. Cement Paint Special cement paints in powder form are mixed with water and used for painting concrete and all forms of masonry. They are superior to the ordinary cement washes, being far more durable and waterproof. Two coats should be used, the first mixed to a fairly thin consistency, and the second much thicker. If brushed on, they are applied with a fibre-bristled bannister brush and scrubbed and dabbed vigorously into the wall surface. They are excellent for finishing and waterproofing the special concretes

mentioned previously. Cement paints are now used frequently instead of the more laborious and expensive plastering of walls with mortar. Plastering Walls and floors of concrete are frequently plastered or “rendered” with a of mortar composed of 2 or 3 parts sand to 1' cement, to give a pleasing finish and to assist with waterproofing. Plastering requires considerable practice and patience to make a good j(sb. It is rubbed on to the concrete with a wooden float, and for a very smooth finish can be .rubbed over with a steel float. Important points in plastering are: First scratch the concrete wall thoroughly, while still “green,” with a pointed steel trowel, wet the wall thoroughly, and do not attempt to plaster, more .than f” thick. Waterproofed cement can be used when plastering water tanks.