If the footings are of concrete, an inspector should be put on the work to stay during the entire working hours, and see that every batch of concrete is mixed in exactly the proportion specified, and that the aggregates are broken to the proper size and the cement all of the same brand and in good condition. There is no building operation that can be more easily "skimped" without detection than the making of concrete, and the only way by which the architect can be sure that his specifications have been strictly followed is by keeping a reliable representative constantly on the ground. The inspector should also see that the concrete is put in to the full thickness shown on the drawings, and that it is leveled and tamped every 6 inches in depth.
Should water be encountered in the trenches, it should be collected in a shallow hole and removed by a pump or drain, as explained in Section 31. Very often, when the foundation rests on the top of a ledge, underlying gravel or clay, running water will be encountered in the trenches in too great a volume to be readily removed. In such a case, the flow of the water should be intercepted by a drain and cesspool, and a tight drain carried from the latter to a sewer or to a dry well below the foundation of the building.
Concrete footings for piers not more, than 4 or 5 feet square may be built, where there is running water, by making large bags of oiled cotton and sinking them in the pit, filling the concrete into them immediately. The water will probably rise around the bag, but if the latter keeps the water away from the concrete until the cement has had time to set, it will have answered its purpose. Water does not injure concrete, or mortar made of cement, after it has begun to harden, but if freshly-mixed concrete is thrown into water the water separates the cement from the sand and aggregates, the cement mixing with the water and floating away, while the sand and stone drops to the bottom. For this reason concrete should never be thrown into trenches containing water.
86. If the footings are of stone the presence of water does not do as much harm, provided the water can be drained so as not to attain a greater depth than 3 or 4 inches. Sometimes the bottom of the wall is used as a drain for collecting the seepage water, and the trench is partially filled with stones laid without mortar, as explained in Section 10.
For heavy buildings, however, the footings should be solidly bedded in cement mortar when the trenches are reasonably dry, and when this is not the case, in sand or fine gravel. An irregular footing stone can often be bedded more solidly by piling fine sand around it and then washing the sand under the stone with water, than it can in cement mortar. The former method, however, takes more time, and would seldom be employed where mortar could be used as well.
As stated in Section 72, too much care cannot be bestowed upon the footing courses of any building, and there is no portion of the building that needs closer inspection than the footings and foundation.
Before the masons commence actual operations the architect should inspect all materials that have been delivered, to see that they are of the kind and quality specified.
The mortar, together with the sand, cement or lime, should be particularly examined, to see that the mortar has the proper proportions of cement or lime, and is well worked; that the cement or lime is fresh and all of the kind or brand specified; and that the sand is clean and sharp. The building of the foundation wall should also be carefully watched to see that the wall is well tied together with plenty of three-quarter and through bond stones, and that the inside is solidly filled with stone and mortar.
The superintendent must also examine the wall occasionally to see that it is built straight and plumb, and that the general bed of the courses is horizontal.
When inspecting stonework already built, but which has not had time for the mortar to harden, a light steel rod, about 3/16 inch in diameter and 4 or 5 feet long, will be found useful. If the rod can be pushed down into the centre of the wall more than 18 inches or 2 feet in any place it shows that the stones have not been lapped over each other, and if this can be done in several places the inspector should order the wall taken down and rebuilt. The rod will also indicate to a considerable extent whether or not the stones in the centre of the wall have been well bedded, as if they have not they will rock or tip when struck with the rod.
The inspection of a foundation wall cannot be too thorough, as there is nothing that causes an architect so much trouble as to have settlements in the foundations of his buildings.
In buildings where the cellar floor is 6 feet or more below the ground level the trenches behind the walls should not be filled in until the floor joists are on and the wall built 6 feet or more above them, or until the walls are solidly braced with heavy timbers, otherwise the wall may be sprung by the pressure of loose dirt. In heavy clay soils it is a good idea to fill in back of the wall with coarse gravel, stone spalls and sand, as frost will not "heave" them as it does clay.
Holes for Soil and Supply Pipes. - In thick walls, and when built of heavy stone, the architect should locate the position of the soil and supply pipes, and see that openings are left in the proper places for the pipes to pass through the wall.