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WATERPROOFING Concrete To the Editor of the SCIENTIFIC AMERICAN: Two or three recipes have been published in your paper, at various times, for waterproofing concrete. There seems to be a good deal of popular misconception on this subject, and it has occurred to me that a few notes I have gathered on the subject during a number of years' experience superintending concrete work, might be of interest to your readers. No concrete can be made entirely waterproof. The best concrete, if subjected to water under high heads, will leak considerably. And even under very low pressures there is leakage, though it is so slow that the water leaking away evaporates as fast as it leaks and leaves an apparently dry surface. But, for practical purposes, a 1: 2 : 4 mix, if made of a medium consistency and thoroughly tamped in place, will be waterproof under small pressures, say up to 15 pounds to the square inch. The more thorough the ramming, the more nearly waterproof the concrete. I have seen one case in which the pneumatic rammer was used, where the concrete was sensibly waterproof under 40 pounds per square inch pressure, without any further treatment. Various compounds of alum and lye or soap are often mixed with concrete, to increase its waterproofing. One of the best known of these was published in a recent number of the Scientific American. Add three fourths pound of dry powdered alum to each cubic foot of sand and dissolve three fourths pound of soap in each gallon of water. Use one part of cement to two parts of sand and four parts of gravel. But I question whether the gain made by this method is worth the extra trouble. The same result can be reached by washing the surface of the concrete on the water side with a wash of one part concentrated lye and two parts alum, dissolved in sixteen parts water. Two or three coats of this solution should be applied, allowing time for each coat to dry, before putting on the next. This method is much less troublesome than the previous method and gives results as good. Another method in common use is to add from 5 to 10 per cent of hydrated lime to the cement before mixing. the proportions of mix being one part of the cement-lime mixture, two parts sand, and four parts gravel. This gives very good results, though it weakens the concrete slightly. On small jobs, where the cost is not of very great importance, a mixture of one part cement, one part of sand and two or three parts gravel, without any further treatment, is waterproof against moderately high pressures. The writer has seen one case, that of a pressure pipe line, where a lO-iiich wall of this mixture was sensibly watertight against a pressure of about 65 pounds per square inch. But, in most cases, the cost of so rich a mixture is prohibitive. Where concrete must be waterproofed against very high pressures, none of the above methods seems to be effective, and other means must generally be resorted to. The usual practice under these conditions is to coat the surface on the water side with asphalt, pitch, or alternate layers of pitch and tarred felt. Paraffine, melted and applied hot with a brush, has also been used very successfully, but this is rather costly where there is a large surface to be covered. Seattle, Wash. Leo G. Hall, Civil Engineer. The Engineering Foundation Organized HOME months ago announcement was made of a gift Sof 250,000 by Ambrose Swasey of Cleveland, which was to be the nucleus of a fund to be devoted to research work in engineering lines and to the promotion of the interests of the engineering professions. No further contributions to the fund have been made, but the Engineering Foundation has been organized. at a recent meeting at the Engineering Societies Building, 29 West Thirty-ninth Street, New York, with the following officers : Gano Dunn, chairman; Edward D. Adams, vice-chairman; F. R. Hutton, secretary; and Joseph Struthers, treasurer. A large number of applications from those who desired the use of some of the funds for research work were already on tile, but these will be held pending the tiling of further specifications in accordance with forms to be drawn up hy a committee appointed for the purpose.
