As a binding material, only mortar composed of coarse sand or river sand and of good cement, should be used. Instead of coarse sand, crushed slag, well-screened, may be employed. The mortar should consist of 2/3 slag and 1/3 cement. Oil should not in any way come into contact with the mortar; it may percolate through the cement and alter its resistant qualities.
As in the construction of all foundations, care should be taken to excavate down to good soil and to line the bottom with concrete, in order to form a single mass of artificial stone. A day or two should be allowed for the masonry to dry out, before filling in around it.
When the engine is installed on the ground floor above a vaulted cellar, the foundation should not rest directly on the vault below or on the joists, but should be built upon the very floor of the cellar, so that it passes through the planking of the ground floor without contact.
[Illustration: FIG. 54.--Method of building the foundation.]
When the engine is to be installed on a staging, the method of securing it in place illustrated in Fig. 55 should be adopted.
Although a foundation, built in the manner described, will fulfill the usual conditions of an industrial installation, it will be inadequate for special cases in which trepidation is to be expected. Such is the case when engines are to be installed in places where, owing to the absence of factories, it is necessary to avoid all nuisance, such as noise, trepidations, odors, and the like.
[Illustration: FIG. 55.--Elevated foundation.]
=Vibration.=--In order to prevent the transmission of vibration, the foundation should be carefully insulated from all neighboring walls. For this purpose various insulating substances called "anti-vibratory" are to be recommended. Among these may be mentioned horsehair, felt packing, cork, and the like. The efficacy of these substances depends much on the manner in which they are applied. It is always advisable to interpose a layer of one of these substances, from one to four inches thick, between the foundation and the surrounding soil, the thickness varying with the nature of the material used and the effect to be obtained. Between the bed of concrete, mentioned previously, and the foundation-masonry and between the foundation and the engine-frame, a layer of insulating material may well be placed. Preference is to be given to substances not likely to rot or at least not likely to lose their insulating property, when acted upon by heat, moisture or pressure.