WATERPROOFING, the art of rendering various substances impervious to the penetrating action of water. The purposes to which water proofing is now applied are very numerous and the methods range from the early use of lead for sheathing building foundations, of tar for tarpaulin, oil for oil-skin, rubber for clothing, to various painting processes which claim for bases, substances capable of resisting the natural action of the elements, and which, invisible, im penetrable, insoluble and imperishable, effectually render brick, stone, marble, terracotta, stucco, concrete, etc.. impermeable to water. These processes are used to waterproof and insulate exterior and interior walls of buildings, for cold storage plants, for the lining of reservoirs, for monuments, etc.
Among the numerous methods of water proofing, many of which are protected by pat ents, the greater number in general relate to a surface application of some composition, usu ally somewhat thicker than an ordinary liquid solution. The more widely known methods of waterproofing are those used in connection with paper and paperboard, textile fabrics, cloth, with cordage, leather, etc.
Paper.— The commonest process for water proofirg paper and manufactures of paper is their saturation with wax or paraffine; either by the use of heat, or in solution, as with benzol. Flexible papers (and woven fabrics also) of an absorbent nature may be made waterproof by a half-and-half mixture of a vegetable oil— such as China wood oil, linseed oil, poppy seed oil or soya bean polymerized cuma rone. The mixture is heated for a time, and after being allowed to cool, is dissolved in a volatile solvent, which is applied with a brush, or by dipping the material into the solution and draining off the surplus. This treatment does not affect the folding qualities of papers, prac tically doubles the tensile strength, and renders the sheet transparent. One of the newest methods, recently patented, consists in saturat ing the paper with an ammonia soap of steane acid emulsified with pare/Tine and diluted with water. The paper is passed through, a tank inaining the emulsion, and thence is taken over a series of drying rolls to evaporate the water. A French process recently introduced consists in coating the paper with a vegetable mucilage, and, after this is dry, applying a coat of agar-agar. The paper thus prepared is then subjected to the steam arising from a bath made by adding four pounds of formol and five pounds of potassium hichromate to six quarts of water. This process renders the paper some what brittle, and to restore flexibility it is sponged with a weak dilution of glycerine. The so-called Japanese waterproof paper is made by pasting two sheets of paper together, the fibres crossing, with a secret waterproof cement.
Water-repellent textiles may be grouped into two classes according to their nature, first, the coarser tissues used for awn ings, tents, oil-skins, tarpaulins or canvas cover ings for exposed merchandise, etc.; secondly, the finer tissues employed for the manufacture of waterproof clothing. The processes em ployed are of two classes, mechanical and chem ical. In the first, a solid layer of some im permeable substance is laid upon the material. The substances usually applied are india rub ber, varnish, resin, pitch, tar, pants, etc. These are also impervious to air. The agents in use for chemical waterproofing are aluminum sul phate, common alum, lead acetate, copper sul phate, zinc sulphate, iron sulphate, ammonium cuprate, potassium chromate, paraffin, ceresine, wax. soap. etc. In waterproofing loosely woven fabrics it becomes necessary to fill up the inter stices between the threads with imperviable material as well as to waterproof the threads themselves. It follows that a textile which is to be waterproofed should be very tightly woven so that when the individual threads are made impervious to water the cohesion of water falling upon it will prevent its separation into particles so small as to be able to pass between the threads. The earliest process consisted in covering the tissue with tar, a method still em ployed for marine supplies, ropes, cordage and coverings, and which has the advantage of giv ing solidity to the fibre, and at the same time preserving it. Drying oils, and particularly boiled linseed oil, are still largely used to water proof coarse tissues, and particularly for the oilskin overalls worn in rough weather by sail ors and fishermen. Oiled tissues, however, are heavy and lack comfortable suppleness, while their color and appearance militate against their extended use. One of the more widely employed processes for waterproofing the coarser tissues consists in impregnating the material with an insoluble soap such as those formed with copper, iron, zinc and alumina. Copper soap is most universally used The material to be waterproofed is first scoured by boiling with soda lye and then washed, after which it is passed through a 20 per cent am monia soap bath, then immersed in an 8 per cent solution of sulphate of copper. Ac cording to its nature, the fibre absorbs a certain quantity, large or small, of copper soap. In the ashes produced by the burning of a square yard of canvas or linen tissue so treated, as much as 57% grammes of copper is found, and nearly 29 grammes of copper is to be found in the enders of the same quantity of cotton tis sue. Copper-soap waterproofed materials pre sent a characteristic greenish tint.