CONCRETE FENCE POSTS.

Sun (Christchurch), Volume I, Issue 47, 1 April 1914, Page 11

CONCRETE FENCE POSTS.

EASY METHOD OF MANUFACTURE HOW TO REINFORCE THEM. Wooden posts are becoming expensive, ami what is move important, their life is limited;- It becomes necessary to find a durable substitute. One of . the most satisfactory, from an all-round point of view, is posts of reinforced concrete. Their manufacture may be undertaken on farms when climatic conditions render other outdoor work impossible. A good supply of shingle and cement, with the necessary moulds for manufacture placed in or near a shed, would provide profitable employment for many a rainy day. The Railway Department are now using con-

Crete fence posts'in some parts of tho Canterbury province; On this substitute an' interesting 'farmers' bulletin, has been- issued by the Agricultural Department of- the United States. A fenee post, to prove thoroughly satis* factory, must fulfil three conditions: (1) It must be obtainable at a reasonable cost; (2) it possess sufficient strength to meet the demands of general farm use; (3) it must not be subject to decay, and must be able to withstand successfully the effeets "of •water, frost and fire. Although iron posts, of various designs are frequently used for ornamental purpose, their adoption for general farm use is prohibited by their excessive cost. Then, too, iron posts expose/a to the. weather are subject to corrosion, to prevent which necessitates repainting from time to time, and this item will entail considerable expense in cases where a large number of posts are to be used. At the present time, the material' which seems most nearly to meet these requirements* is reinforced concrete. The idea of constructing fence posts of concrete reinforced with iron or steel is by no means a new one; but, on the contrary, such posts have been experimented with for years, and a great number of patents have been issued covering many of the possible forms of* reinforcement. It is frequently stated that a reinforced concrete post can be made and put in the ground for the same price as a wooden, post. Of course, this will depend in any locality upon the relative value of wood and the various materials which go to make iip the concrete post; but, in the great majority of cases, wood will prove the cheaper material with regard to first cost. On the other hand, a concrete post will last indefinitely, its strength increasing with age, whereas the wooden post must be replaced at short intervals, it more expensive in the long run. In regard to strength, it must be borne in mind that it is not practicable to make concrete, fence posts as strong as wooden post's of the same size; but since wooden posts, as a rule, are many times stronger than is -Heeessary, this difference in strength should not condemn the use Of Veinforced concrete for this purpose. Mofeover, strength in many cases is of little importance, the fence being used only as a dividing, line, and in such cases small, concrete posts provide ample strength, and present a very unifbrm and neat appearance. In any case, to enable concrete posts to withstand the loads they are called iipon to carry, sufficient strength may be secured by means of reinforce ment, and where ;great strength is required, this, may be obtained by using a larger post with a greater proportion of metal and wesll braced, as is visual in such cases. In. point of durability, concrete is unsurpassed by any material of construction. It offers a perfect protection to the metal reinforcement and is not itself affected by exposure, so that a post constructed of concrete reinforced with steel will last indefinitely, and require no attention in the way of repairs. REINFORCEMENT.

No form of wooden reinforcement, either on tlie surface or . within the post, can be recommended. If on the surface, the wood will soon decay, and if a wooden core is used it will, in all probability, swell by the absorption of moisture and craclt the post. The use of galvanised wire is sometimes advocated, but if the post is properly constructed and good concrete used this precaution against rust will be unnecessary, since it has ""been fully demonstrated by repeated tests that concrete protects steel perfectly against rust. If plain, smooth wire or rods are used for reinforcement they should be bent over at the ends or looped to prevent slipping in the concrete. Twisted fence wire may usually be obtained at a reasonable cost, and, it is very suited for this purpose. Barbed wire has been proposed and is sometimes used, although the barbs make it extremely difficult to handle. For the sake of economy, the smallest amount of metal consistent with the desired strength must be used, and' this requirement makes it necessary to place th® reinforcement near

the surface, where its strength is utilised to greatest advantage, with only enough concrete on the outside to form a protective covering. A reinforcing member in each corner of the post is probably the most efficient arrangement. CONCRETE FOR FENCE POSTS. The concrete should be "mixed with Portland cement in about the proportion broken stone or gravel under one-half inch being used. In cases where the aggregate contains pieces smaller than one-fourth inch, less sand may be used, and in some cases it may be omitted altogether. A mixture of medium consistency is recommended, on the ground that it fits the moulds better and with less tamping than if mixed quite dry. MOULDS FOR FENCE POSTS. Economy points to the use of a tapering post, which, fortunately, offers no difficulties in the way of moulding. All things considered, wooden moulds will be found most suitable. They can be easily and quickly made in any desired

size and form. Posts be moulded either ih a vertical or horizontal position, the latter being the simpler and better method. . If moulded vertically, a wet mixture is necessary, requiring a longer time to set, with the consequent .delay in removing the moulds. Tig. 1 shows a simple mdiuild which has been used with satisfactory results in this laboratory. This mould has a capacity of four posts, but larger moulds could easily be made on the same principle. It consists of two end pieces carrying lugs, between which are inserted strips. The several parts are held together with hooks and eyes, as shown in Fig. 1. To prevent, any. bulging of ;tlie.-side strips, they are braced as illustrated. Dressed lumber at least lin thick, and. preferably !Uin, should be used. In Fig. 1 the post measures 611* x 6in at the bottpip, <sin x 3in at the top, and 7ft in length, having two parallel sides. If it is desired to have the posts square at both ends, the moulds must be arranged as in Fig. 2. This latter form •of post -is not as strong as the Jbut requires less concrete in its construction. Great care in tamping is i necessary to ensure the corners of the mould being well: filled, and if this detail is-not carefully watched the metal, being exposed in places, will l be subject to rust., - . .

ATTACHING FENCE\ WIRES TO POSTS. Various tWKrieesf have been suggested for attaching fence wires to the posts, the object of each being to* secure a simple and permanent fastener, or one admitting of easy'-renewal at any time. Probably nothing will answer this purpose better than a long staple, or bent wire, well embedded in the concrete, being twisted or bent at the end to prevent extraction. Galvanised metal must be used for fasteners, since they are not protected by the concrete. A piece of small flexible wire, about two inches in threading the staple and twisted times with a pair of pliers, holds the line wire .in position. (Fig. 3).

MOULDING AND CURING POSTS. It is recommended that only so much concrete be mixed at one time as can be used before it begins to harden; but if an unavoidable delay prevents the posts being moulded until after the concrete has begun to set, it is thought that a thorough re-gauging with sufficient water to restore normal consistency will prevent any appreciable loss of strength, though the concrete may have been standing one or two hours. In using a mould similar to that illustrated, it is necessary to provide a perfectly smooth and even platform of a size depending upon the number of posts to be moulded. A cement floor, if accessible, may be used to advantage. The moulds, when in place, are given a thin coating of soft soap, the platform or cement floor serving as bottom of mould being treated in the same way. About inches of concrete is spread evenly over the bottom and carefully tamped, so as to reduce it to a thickness of about 1 inch. A piece of board cut as in Fig. 1 will be found useful in levelling off the concrete to the desired thickness before tamping. On top of this layer two reinforcing members are placed about 1 inch from the side of the mould. The : moulds are then filled and tamped in thin layers to the level t>f the other two ranfomuff members, the fasteners for

fence wires being inserted during the operations. These reinforcing members are adjusted, as were the first two, and the remaining 1 inch of concrete, tamped and levelled off, thus completing the post as far as moulding is concerned. To avoid sharp edges, which are easily chipped, triangular strips may be placed in the bottom of th£ mould, along the sides, and when the moulds have been filled and tamped, similar strips may be inserted on top. The top edges may be bevelled with a trowel. The ends sides of the mould may be removed after 24 hours, but the posts should not be handled for at least one week, during wljich time they must be well sprinkled several times daily and protected from sun and wind. The intermediate strips may be CEtrefully,.withdrawn at the end of two ox three days, but it is better to leave them in place until the posts are moved. Although a post may be hard and apparently strong when one week old, it will not attain its full strength in that length of time, and must be handled with the utmost care to prevent injury. Carelessness in handling "green" posts frequently results in the formation of fine cracks, which, though unnoticed at the time, give evidence of their presence later in the failure of the posts.

Posts should be allowed to cure for at least 60 days before being placed in the ground, and for this purpose it is recommended that -when moved from the moulding platform, they be placed upon*a smooth bed of moist sand, and protected from the sun until thoroughly cured., During this period thdy should receive a thorough drenching at least once a day. The life of the moulds, will depend upon the care with they are handled. A coating of mineral oil or shellac may be used instead of soap to prevent the cement from sticking, to the forms. As. soon as the mbulds are removed they should be cleaned with a wire brush before'being used again. ", The cost of reinforced concrete fence posts depends in each case .upon the cost of labour and materials, and must, necessarily, vary in different localities. One cubic yard of concrete will make 20 posts measuring 6x6 inches, at bottom, 6x3 inches at top, and 7ft long, and if mixed in the proportion of -1-2J-5, requires, 1.16 barrels of cement, 0.44 cubic yard ;of sand, and 0.88 cubic yard of gravel. .