Boarding Up Forms

Walls for small buildings, such as garages, milkhouses and many small farm buildings are usually not more than 6 inches thick. One set of forms is usually set up complete before work is started. This may be either outer or inner form, but the other one should not be completely boarded up before concreting has commenced because if both forms are boarded up to a height of 8 or 10 feet, it will be impossible to place concrete in this narrow deep space and spade it or otherwise compact it so that a regular, smooth surface finish is secured. Another objection to placing concrete in deep forms is in dumping the mixtures through such a height, pebbles or broken stone are likely to separate from the sand-cement mortar and this will cause varying density in the concrete because of pebble pockets due to separation of materials. One form should be boarded up only as concrete is placed, say, 2 feet at a time. This will permit the concrete to be thoroughly spaded, which will make certain of a better surface.

Protecting The Finished Work

Proper protection of concrete work after the actual concreting has been finished is of utmost importance. As already mentioned, the action that causes concrete to harden is brought about by the chemical combination of cement and water, and this hardening action, although commencing very soon after concrete is mixed, is not complete for a considerable length of time. Complete hardening requires a length of time that varies. It is dependent upon the amount of water used in the mixtures and the season of the year, that is, whether summer or winter. Concrete hardens slowly in cold weather. It hardens rapidly in warm weather if other conditions are favorable, and this means protecting it so that the water which was used in the mixture will not be lost by evaporation or otherwise.

In some classes of work, especially where the mass is considerable, leaving forms in place for a few days affords all the protection necessary. If, however, forms are removed and the weather is hot and dry, the work should be sprinkled several times daily to prevent loss of water by evaporation and also to make the concrete harden more uniformly.

If a concrete flower box is being made, it will, under favorable conditions, be possible to remove the forms within from 12 to 24 hours after the last concrete was placed. At this time such imperfections as may appear on the surface are carefully patched up with sand-cement mortar, then the box should be carefully immersed in a tank so that the concrete will everywhere be covered with water. Left to harden in this manner the concrete will acquire more uniform strength within a given time than can be secured by any other equally simple means.

Protecting Walks And Floors

Concrete walks and floors may be protected by covering them with a layer of moist earth or sand, hay, straw or similar material just as soon as it is possible to apply such a covering without marring the surface. This covering should be left in place for several days, depending upon the season of the year and the rapidity with which the concrete hardens under the prevailing temperature conditions. Also, the covering should be kept wet by frequent sprinklings daily during the time it is left in place. Usually concrete walks should not be used until they are at least a week or ten days old.

Walls and exposed vertical concrete faces should be protected from hot sun and drying wind. They can be kept wet by sprinkling. It may be necessary to hang old canvas or burlap so as to protect the surface from the sun's rays.

Concrete work may have been performed with proper observance of all requirements up to the point of protecting the finished work, yet if this is neglected a great part of the • success that would have come from observing other requirements will be lost. It is especially necessary to protect new concrete watering tanks, troughs and other receptacles that are to hold liquids, because too rapid drying out of the concrete will often prevent it from being watertight.