As regards stone, other than such specially crystalline kinds as granite, marble, porphyry, hard limestone, etc. none of which is liable to admit access of water from its external surface - we very much doubt the efficacy of any dressing; such, for instance, as what is called silicon varnish, or anything of the kind. The real and only effective means of preventing crumbling, blowing, or exfoliation is to make sure that the blocks are cut so as to be seated in the structure on their natural beds - that is to say, horizontally parallel to the direction of their natural fissures and lamince, which, in the rock, keep the direction of the dip. The reason is this: water coming into contact with the external surface of a stone, of which the natural fissures are set perpendicularly or at a high angle, will inevitably be admitted into those fissures, and it will follow them down by gravitation, and promote the entry of more water after it until the fissures are full, if such conditions be promptly followed by keen frost, for example, the water so admitted is apt to be congealed and thus expanded, and then to prise the laminae asunder, and blow out or exfoliate any scale of trifling thickness; and so long as the fissures ard presented externally in such directions, no dressing whatever will effectually protect the stone.
When, on the other hand, the stone is laid on its natural bed, and the fissures and lamina are horizontal, all wet falls harmlessly down the face of the stone (outside). It is never admitted into the substance; and, what is more, most kinds of stone which are subject to such accidents, if preserved by proper placement from the inward access of water, have a tendency to become externally case-hardened in course of time, under outward exposure to the action of air and water, by a slow process of normal crystallization, which ultimately endows them with real durability. (Design and Work).