FIRE-RETARDANT PAINTS FOR SHINGLES Under this title, Henry A. Gardner, Assistant Director of the Institute of Industrial Research, Washington, D. C., discusses the latest results of his tests of fire-resistant paints as applied to shingles. In the first place, he calls attention to the low heat conductivity of a shingle roof in the following language: "The writer conducted a series of laboratory tests to determine the heat deflecting properties of various types of roofing materials. Miniature houses were roofed with bare shingles, painted shingles, tin, and stone. Thermometers were inserted in the end of each house. The houses were placed in an oven heated to 150° C. At the end of 15 minutes, thermometric readings were taken. The interior of the houses roofed with stone and tin showed a much higher temperature than those roofed with shingles. The house with the roof covered with painted shingles showed the lowest temperature. On account of the heat deflecting properties of shingles, they will probably always find a wide application in warm climates. Shingled dwellings are much cooler in the summer than iron-clad or stone-roofed dwellings." After mentioning the usual objections that are made to shingle roofs as sources of fire danger, Mr. Gardner continues: "Although the writer has pointed out in the foregoing discussion, the many disadvantages of the wooden shingle, the situation is not as serious as it might at first appear. Very few structural materials have ever been made which have proved satisfactory for roofing or other building purposes, without some surface treatment. If iron or steel sheets are exposed to the weather, they will rapidly corrode and rust away to a mere lace-like skeleton of their original form. The application of suitable paint coatings at proper intervals, will, however, preserve such metal sheets for an indefinite period of time. Nearly all forms of cement or stone work will check, crack, absorb large quantities of moisture, and become unpleasing in appearance, unless properly treated with protective paints. The weather-boarding and wooden trim of all kinds of structures would soon rot and decay if left in an unpainted condition. It is evident that "paint is the preserver of all things structural," and that we must look to the use of paint for the solution of the problems under consideration.
Two Groups of Fire-Retarding Paints "Fire-retarding paints may properly be divided into two groups, one of which is represented by oil-mineral paints, and the other by paints which do not contain oil. The term "mineral paint" refers to that type of paint which is so widely used throughout the rural districts to decorate and preserve. dwellings, barns, and similar outbuildings. In the manufacture of these prepared mineral paints, various mineral pigments in a finely divided and carefully prepared form are ground in linseed oil, and mixed with the proper driers and thinners. The content of mineral pigment in such paints varies from 50 per cent to 70 per cent of the total. When such paints are applied to shingles, a very durable, waterproof film results. This film of dried paint upon the surface of a shingle has the effect of laying or smoothing down the rough, fuzzy surface of the wood, thus eliminating at once an important source of fire danger. The paint film, moreover, is quite as resistant to moisture as a sheet of India rubber. The shingled dwelling upon which such paint has been used is practically rain-proof. It is, moreover, made very attractive in appearance.
"Another important function is performed by the, paint, in preventing the warping of shingles at the edge, thus doing away with the formation of pockets in which hot cinders might lodge and burn.
"The fourth and most valuable characteristic of mineral paint is its resistance to fire. While the oil content is more or less combustible, there is present in the dried paint film a minor proportion of oil, the major proportion consisting of mineral pigments which are unaffected by fire. A hot cinder or spark, falling upon a roof properly treated with a high-grade mineral paint, would, in most instances, roll from the roof to the ground. There would be no pockets in which to lodge and burn. In the event of hot cinders falling with great force upon relatively flat roofs, the cinders would probably lodge upon the surface and burn away the superficial coating of dried oil, gradually dying out as they reached the fire-resisting mineral pigment.