This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Whether the bearing be piles or the natural earth, the bottom of the foundation will usually consist of large stones or of concrete. If three rows of piles are used they may be covered as shown in Fig. 00. Two rows of piles are generally capped by a series of levelers laid across the trench as in Fig. 97. A footing on earth will be laid in a like manner, and of a width made necessary by the load to be borne and the nature of the soil. The purposes of these wide footings are to spread the weight over a large area and also to add stability to the wall, and they may be of stone, brick, or concrete. For nearly all buildings on solid ground, concrete footings are probably the best, and in many cases concrete capping tor piles may be used to advantage.
Fig. 96. Capping of three Rows of Piles.
Trenches for the footing may be dug below the regular excavation and of the exact width required, and into this the concrete may be tamped (Fig. 98). A good proportion is one part of cement, two parts of sand, and four parts of stone, for natural cement. The thickness of the footing should he one-quarter of its width (provided this does not figure less than twelve inches) put in by layers about six inches each. If this concrete is much wider than the wall over it, a stone leveler may be placed on the top, as shown in Fig. 98 A.
If preferred, stone footings of a similar character may be used, as in Fig. 09, and for light buildings where stone is hard to obtain, brick footings may be used. If this is done, the offsets should never be more than one-quarter of a brick, and the outside work should be all headers, with a double course at the bottom. (Fig. 100.) This course should be laid in a bed of mortar spread on the bottom of the trench, of hard burnt bricks, thoroughly wet if the weather is dry. Too much care can never be taken to insure a good foundation. If important footings are made of concrete, an inspector should be on the work during working hours, to see that the concrete is mixed in proper portions, and put in to the full thickness shown, and tamped and leveled every six inches. The trenches must be kept free from water until the cement has set, or it will become utterly worthless, by reason of the water separating the cement from the sand. If the footing is of stone, the presence of water, if only a few inches deep, will do no harm, but the footing then must be bedded in firm sand or gravel instead of cement.
Fig. 97. Capping of two Rows of Piles.
Fig. 98. Concrete Leveler.
Fig. 99. Stone Footing.