CONCRETE FINISHING FOR A DRAINING – PEN.

New Zealand Journal of Agriculture, Volume XVIII, Issue 4, 21 April 1919, Page 224

CONCRETE FINISHING FOR A DRAINING - PEN.

The following information is furnished by the Public Works Department in response to an inquiry regarding the best method of finishing off the concrete floor of a sheep-dip draining-pen, cement plastering being specially referred to : —

The cement plastering for a draining-pen should be composed of one part of fresh Portland cement to three parts of clean, sharp, fresh-water sand. The concrete should not be finished with a perfectly smooth surface, in order that there might be what is known as a key for the plaster to adhere to. If the concrete bed is laid in sections the plastering should be delayed until all the sections have been finished. The plastering should then be done, if possible, in one continuous operation, so that there would be no weak points in it at the end of one day’s work and the commencement of another. ■ As it is not possible to prevent shrinkage-cracks appearing in concrete of any large extent unless the same is heavily reinforced, it is advisable to put in special joints in order that the cracks may appear along these joints, which would be in .straight, symmetrical lines, and therefore not unsightly. These joints are quite easily made by the insertion of a sheet of brown paper, the method of procedure being as follows : Boxing, say, 12 ft. square by the depth proposed, is made and filled with concrete, the same being spaded down carefully alongside the boards. When this is set sufficiently the boards are removed, brown paper stuck to the vertical edge, and the new concrete filled against this paper.

In order to' expedite work the whole area to be concreted can be divided off into squares, one-half of which could be done at once, every alternate square being left vacant. Then, when the first group of squares has set sufficiently, the whole of the remaining space can be filled up in one operation. If the second lot of concrete, is kept excessively wet for about ten days after it is laid it. will expand in setting and thereby reduce the cracks to a minimum. If a trowel is run along on the top of these joints, through the newly laid plaster, this will ensure the plaster cracking in straight lines exactly in harmony with the squares laid out in the main concreting. The plaster should be approximately | in. thick. Slight variations in its thickness, of course, will be brought about by the fact that the concrete surface is .not absolutely true.

There is really no necessity for plastering such a structure as a draining-pen, for if properly graded gravel be used containing an adequate quantity of fine stuff, and if the mixture be well worked and screeded off, a quite satisfactory finish, may be made without the expense and trouble of plastering. By mixing a small quantity of specially fine stuff and applying it to any portions of the surface which appear rough, and then working over the whole surface with a wooden float or a fairly wide piece of canvas, it is possible to make a really good finish.

In order to ensure an even surface it is advisable to set up a board perfectly true on each side of the work at the height at which it is desired to finish, and then to run a straight-edge between these boards, working the same back and forth, and leading the concrete away from any high places and into hollows until the whole area dealt with is a plain surface. • •