AN ARTICLE FOR FARMERS

Horowhenua Chronicle, 4 March 1915, Page 4

AN ARTICLE FOR FARMERS

CONCRJiTK JJ'OR. TJtUi NOVICE

QUANTITIES TO USE

(Continued.)

A concrete mixture is usually spokan 01 as a 1:2:4 mixture, or a 1:3:6 mixture, etc. If gravel is the only aggregate used, it is more common to speak of a 1:4 or a 1 :(5 mixture. The first number always refers to the cemeit tne middle to the sand, and the last to the coarser aggregate. And the amounts should always Dβ measured y volume. Thus a 1:2 :4 mixture means one part of cement, twice as much eand, and four times as much stones or gravel. As a bag of Crown cement contaUs \.l cubic feet, the corresponding amounts of aggrgeate may be easily calculated for any mixture. A concrete of 1:2 :4 mixture is very strong, and when well made should be waterproof. The corresponding mixture, when a natural shingle and sand", or gravel and sand is used, is a 1:4. A 1:3:6 concrete is strong enough for most purposes, such as floors, foundations, walks, feed trougns ' and in fact, almost any work that does

not require reinforcing. It is advisable to have a measuring Ibox to regulate the quantities of eacti, but failing that, mix three small barrows full of shingle to one small bag of cement for ordinary farm work. The shingle or metal is first tipped on to the mixing board, after measuring the quantity, then the sand spread on top of it (if sand is being used in the mixture) and the cement is emptied evenly all over the pile. Then the heap is turned twice dry, shovelling from under and turning the shovel outwards and over. The water should be sprinkled on the heap so that the cement may not be washed from the aggregate, and then the heap is turned twice wet. Another method is to mix the sand and cement in a dry state first and spread it evenly all over the shingle, scoria, or metal. MIXING BOARD. If timber is scarce a suitable mising floor can be made by selecting h level piece of ground and removing the turf four inches deep from n space ten feet "square, then mix up three barrows full of shingle, scoria, or metal, wnichever is available, to one bap; of cement. Spread it over the ground i-inch thick, after wetting the ground well, and allow to stand for say two days, so that it will set hard. MIXING. There is one universal rule that p.pplies to concrete mixing. That s, mix it thoroughly in the following manner:— Tviixing should begin at the outer edge of the pile; fill fhe shovel, by puching it under and into 'the pile and empty it by turning it over with a fling towards the other side of the board. Start again and reverse ihr operation, bringing the pile back to the original position. Add about three-quarters of the required amount of water, being careful not to wash away the cement by dashing the water on too rapidly. A sprinkling pot with large holes in is an excellent thing to ■ se on small jobs. Now turn again as be fore, adding water to the dry spot* wherever necessary- Instead of flinging the material from the shovel, as before, turn it out and pull the shove , back through it. This will cause the wet gravel to pick up any cement am sand through which it is dragged ; don'l dig into it. Turn twice or until tin concrete has no dry spots or streaks adding enough water to bring it t( the proper consistency, but always shovel from the bottom of the heap. When placing the concrete into ; barrow or carrier always shovel if fron the bottom of the heap turn the shove ■ over into the barrow. CONSISTENCY. Consistency will be determined large ly by the use to which the concrete 1: being put. For floors, foundations thick walls, and work that is easil: tamped, what is a jelly-like mixture that quakes and brings" water to th< surface when tamper. A man stand ing on such a mixture would sink thre< or four inches. For work where tamp ing is hard to do, or where watertight ness is an object, a wetter mixture i better. The writer has found a mix ture that takes a slight shake to ge it off a shovel to be the best for mos purposes. Such a mixture should b< not tamped, but puddled. Take > spade or thin board with a eharp edg< and churn it up and down in the con crete, particularly next to the forms This will make a dense, smooth suifac* by forcing the coarser portions awa; from the forms. In general, the wet ter the concrete the longer it takes t< set hard. Therefore a large exces of water should be avoided.

PLACING.

Placing should be done immediately after mixing. Wherever possible, a job should be finished without letting any part set for longer than half an hour before adding more concrete, as joint planes are almost sure to occur when a longer time elapses between placings. Wherever it is necessary to place concrete on or joining work that has already set, the latter should be well cleaned and roughened, and a grout or paste of cement and water poured over it before the fresh concrete is placed. Where it ie necessary to join now work to very old work, it ie best done by roughening the old surface and washing it with a weak solution of hydrochloric (muriatic) acid. After the acid has frothed for a few minutes, wash it off *horou>ghly with water, and

put on a paste of cement and water i as above. I Care should be taken to keep the I concrete wet and shaded from the r.un , for a least a week after being placed. ' This is essential to the making of good ' concrete. Damp bags laid on the sur- , face and kept moist are generally usad. Don't use dirty material of any kind. Don't throw the water on all at once. Don't mix more concrete than can be used up within half an hour. Don't sprinkle dry cement over the surface of fresh concrete work. Don't unless absolutely necessary let the base nr body of a piece of concrete eet hard before putting on the finishing coat, if there is to be one. EXPANSION AND CONTRACTION JOINTS. Cement concrete expands and jontracts by changes of temperature in , the same way as steel. It ia, therefore, necessary to cut joints which will allow for this expansion and contraction. The concrete must bo cut entirely through to the bottom of the slab with a trowel, cleaver, of other instrument, the joint formed being from J inch to i-inch wide. Blocks formsd in this way should not be greater than 6 feet square (36 square feet). TOOLS. Tools.—The necessary tools are: shovels, .water buckets, or barrows for depositing concrete, measuring bpx, mixing board, and tamper or puddhr The mixing board should be not smaller then. 10ft. x 9ft., with the upper side surface to make shovelling easy. The joints should be tight, to prevent leakago of cement and water. A 4in. x 2in. or 2in x 2in piece nailed around the edge will save waste. The puddlar should be made of a piece of 4in.x ""in. of convenient length. At the lower end it should be tapered on one edge. A water barrel, a rake, a tamper, and a sand screen are tools that vre often used in addition to the ones given above. (To be continued.)