Concrete Mixture For Posts

A 1:2:3 mixture is used for concrete fence posts. Pebbles or broken stone should not be larger than 1/2 inch. The mixture should be slightly wetter than the one described as quaky, but not so wet the pebbles will separate from the sand-cement mortar. After the molds have been oiled, 1 inch of concrete should be spread evenly at the bottom, then two reinforcing rods of the proper size and length should be laid in the concrete at the correct distance from the sides of the form. These rods should be pressed gently into place and held a proper distance from each other and from the sides of the mold by passing over them four or five wire spacers. A piece of hay baling wire looped around the rods will serve the purpose. Additional concrete may then be placed up to within 3/4 inch of the top of the mold, when the remaining two rods, also with spacers over them, should be placed exactly as were the first two. The remaining space in the mold should then be filled with concrete and the surface smoothed with a wood trowel.

To make a post that will have a smooth surface and dense structure it is necessary that while the concrete is being placed any air that may have been trapped in it by mixing be forced out. Various types of commercial fence post molds are filled by one of two methods. Sometimes the molds are set up on one end and filled from the other. In other cases the molds are open at one side and are filled while lying in a horizontal position. When the former type of mold is used the air bubbles can be forced out by repeatedly raising and dropping the mold while the concrete is being placed or by stirring the concrete slightly with a stick or rod, tapping the mold while filling it. In the latter case the mold may be shaken, jarred or rapped or a thin stick or rod dragged through the concrete and along the inside surface of the mold, thus helping to release the air bubbles. These methods properly used will, if the concrete mixture is of the right consistency, give a dense post, with a smooth surface finish showing few if any pebble or air pockets.

After molds have been filled they must remain undisturbed until the concrete has hardened sufficiently to permit removing the posts from the molds without damaging them. Under favorable conditions such as prevail during summer weather, the side pieces of the mold may be removed at the end of twelve hours. It is important that the concrete shall have hardened sufficiently so that when removing the molds the concrete will not be injured. For this reason a wood mold should be built so that wedges and blocks only will be necessary to hold all parts assembled, thus making it possible to take the mold apart with the least amount of hammering. After a post is made it must be given time to harden and gain strength before being used. In other words, it must be "cured." This is done by keeping it damp for several days. A covering of hay or straw and frequent sprinkling during each day for at least a week will accomplish the purpose.

In regular manufacturing plants where concrete posts are made commercially, they are usually cured or hardened by steam, which properly used will accomplish as much in 48 hours as can be done in a week or more by the sprinkling method. But as steam hardening cannot usually be arranged for outside of the commercial plant, it will not be discussed in detail here.

After a post has been kept moist by a protective covering properly sprinkled for a week or more, it will be strong enough to be moved if handled carefully. No post should be subjected to the strains of a fence line until it is at least a month old. Weather is an important factor in the hardening of concrete. The speed of hardening is much more rapid in mid-summer than at other seasons, and when the temperature is near freezing the rate of hardening is very slow, therefore the time of hardening must be lengthened in accordance with the season and weather conditions. Posts made during cold weather must be protected from freezing until thoroughly hardened, as must any other concrete work under the same conditions.

Corner and gate posts are always more massive than ordinary line posts and as a rule these larger posts are cast in place by first making the proper excavation, then setting up the necessary forms, placing reinforcing and depositing concrete from one end of the mold. If the post is to be used for hanging a gate, suitable provisions must be made in the mold and while placing concrete to embed in it the necessary gate hanging fittings. Also, such a post should be allowed to stand for 30 days or more until it has gained sufficient strength to allow hanging the load of the gate upon it.

Home-made wood forms for fence posts.