PAINTING AND GLAZING.
labor of the painter consists chiefly in applying an im pervious covering or coating, of which drying oil is the base, to buildings as preventive of decay and for purposes of ornament. In outside work the chief aim should be protection from the alternations of cold and heat, wet and drouth, and, incidentally, from sulphurous gases present in the atmo sphere, especially in manufacturing cities. When durability in timber is of primary consideration, some authorities suppose that the rough surface left by the saw offers the best resistant against weather; and when the wood has not been properly seasoned, the application of paint and varnish has the effect of causing dry rot by confining- the interior moisture within the timber.
principal material used in house-painting is either white lead or oxide of zinc, ground in unboiled linseed oil to the consistency of paste. As a preparation for immediate use, it is finther thinned by the addition of more linseed oil. Driers are added, to hasten the process of hardening, as each coat should dry thoroughly before the next is applied. Litharge, japan varnish, sugar of lead, and sulphate of zinc are used as driers. Turpentine as a thinner should be used sparingly in outside work, as it is apt to impair the firmness of the paint, and to cause it to blister under the heat of the sun. Various compounds have recently been intro duced to meet objections to the ordinary lead and zinc paints, based on their poisonous nature, chemical effect upon metals, sensitiveness to vari ous gases and vapors, and offensive stnell. The evaporation of turpen tine proves very injurious to the health of many persons, and paints have been invented in which lead and zinc may be mixed with methylated spirit containing shellac, with a small quantity of linseed and castor oil. The spirit, evaporating-, allows the shellac to set as a substitute for the film of varnish deposited in common paint by the oil and turpentine.
For exterior use, anti-corrosive paints made of equal parts of white lead and ground glass have been extensively manufactured. As waterproof defences, silicates have been introduced successfully. What have been
styled " indestructible " paints have been composed of oxides of zinc and lead, with petroleinn.spirit holding- resinous matter in solution. Paints of oxide of iron combine intimately with iron, forming a durable protection against dampness. Tinned iron exposed to weather is well protected by Spanish-brown paint, and lime with sulphate of zinc makes an excellent wash for exposed walls of brick ancl stone. Fireproof paints and washes are effectual when combined with silicates. Sulphate of lime, with coal tar, diluted with naphtha, is also durable against weather. Pitch and wood tar are used extensively as preventives to dampness. Other applications have for their object the protection of stonework against deterioration from atmospheric causes. They are chemical washes, of various composition, which by their presence prevent the destruction of the surface of the stone. The Houses of Parliament have been subjected to treatment of this nature, but with indifferent success.
Painter's first coat, or priming, for outer woodwork is composed of lead mixed with raw linseed oil, with a drier of litharge ground in turpentine. This composition sinks promptly into the wood and hardens upon the surface, preparing the way for any after-treatment and economizing- the paints applied later. Some authorities advise that tur pentine should not be used in this priming. After this coat is dry, all holes are carefully stopped with putty, so as to present a smooth surface for the more ornamental coats to follow. The putty used for this purpose is composed of whiting kneaded with linseed oil, white lead being added to increase the hardness. Painter's work is frequently estimated by the square yard, it being supposed that a pound of paint covers four superficial \ a rcl s in the priming, or first coat, and six yards in each of the subsequent coats, and that a pound of putty is used in every twenty yards. A day's work on the outside of a building has been estimated at too yards of the priming and So yards for each of the outer coats.