Durability of Building Stones.—Dr. Alexis A. Julien has made examinations of buildings of various ages, and of tombstones in some of the older grave-yards around New York city, to assist in determining the durability of the various stones used in building. The coarse brown-stone, which is largely employed, appears to be one of the most perishable materials in use, so that many builders are returning to brick, although the finer varieties of brown-stone are better and compare favorably with other materials. Among the causes for the decay of this stone are mentioned, erection on the edge of lamination, the heat of the sun on exposed sides, and imperfect pointing, with poor mortar, which falls away and leaves the joints exposed to the weather. The presence of sea-salt in the atmosphere has exerted no appreciable effect, and lichens growing on the stone do not appear to have occasioned any decay or corrosion. The light-colored Nova Scotia sandstones have been too recently introduced to show marked defect, but evidences of exfoliation and of slight moldering in damp spots have begun to appear. Buildings constructed of the Amherst (Ohio) sand-stone show little decay, only discoloration; and that is regarded as a favorable sign rather than otherwise, for it indicates durability, while a stone that cleans itself does so by disintegration of its surface, the grains dropping out and carrying away the dirt. The coarse fossiliferous limestone from Lockport has disintegrated rapidly within the last ten years, chiefly on account of careless arrangement in masonry. The oölitic stone from Ellettsville, Indiana, shows an almost immediate and irregular discoloration, said to be produced by the exudation of oil. The oölite from Caen, France, has shown decay in several instances where it was not protected by paint. The dolomitic marble of Westchester County has decayed considerably after sixty years of use, but much of this is owing to the stone having been improperly laid. Often marbles, of various kinds, in tombstones, are in fairly good condition. Horizontal slabs show a tendency to bend. The frequent obliteration of inscriptions, the general and often rapid granulation of the surface, and the occasional Assuring of slabs, show that the decay of marble—in the varieties hitherto long used in New York city—is steady, inevitable, and but a question of time; and, if unprotected, this material is likely to prove utterly unsuitable for out-of-door use, at least for decorative purposes or cemetery records, within the atmosphere of a city. A blue-stone, or graywacke, is yearly coming into more general use, and, though somewhat somber in tone and difficult to dress, seems likely to prove a material of remarkable durability. The bluish Quincy granite has been used in many buildings, and rarely shows as yet many signs of decay. A fine-grained granite from Concord, New Hampshire, also promises to be durable. The light-colored and fine-grained granite of Hallowell, Maine, in which the white feldspar predominates, has shown some exfoliation, but in the single building in which this is remarked the stones appear to have been set on edge, and, as their structure is laminated, that is an important matter. "The weathering of granite does not proceed by a merely superficial wear, which can be measured or limited by fractions of an inch, but by a deep insinuation along the lines of weakness, between grains, through cleavage-planes, and into latent fissures. Thus, long before the surface has become much corroded or removed, a deep disintegration has taken place by which large fragments are ready for separation by frost, from the edges and angles of a block. When directly exposed to the heat of the sun, an additional agency of destruction is involved, and the stone is suddenly found ready to exfoliate, layer after layer, concentrically." The following is an approximative estimate of the "life" of different kinds of stone, signifying by the term life, without regard to discoloration or other objectionable qualities, merely the period after which the incipient decay of the variety becomes sufficiently offensive to the eye to demand repair or renewal: coarse brown-stone, five to fifteen years; laminated fine brown-stone, twenty to fifty years; compact fine brown-stone, one hundred to two hundred years; blue-stone, untried, probably centuries; Nova Scotia stone, untried, perhaps fifty to two hundred years; Ohio sandstone (best sili-
Page:Popular Science Monthly Volume 24.djvu/875
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