Paint for Iron Surfaces.

Manufacturer and builder 7, 1875

A writer in the Painter's Magazine says that the best linseed oil, with all its advantages, is but poorly adapted to long service as a protection to iron surfaces exposed to extreme variations of temperature and to all kinds of weather; but that in selecting a paint fur such purposes, mechanical adhesion is a consideration of the first importance. In this respect paints differ widely, but it must be remembered that mechanical adhesion is all we have to depend upon. With absorbent surfaces it is different. Prof. Williams gives it as his opinion, based on observation and experiment, that pitchy or bituminous films are especially effective as regards their adhesion to iron, for example, solutions of asphalt or pitch in petroleum or turpentine. These are also very effective as regards continuity, owing to the fact that, in drying, they form plastic films, which yield to the expansion and contraction of the iron, and manifest no tendency to crack. If the surface is rusty, they penetrate the oxid scale and envelop the particles very effectually, making them a portion of the paint. The solubility of such a film in water may be counteracted by mixing it with linseed oil. The experiment may easily be tried by mixing about two parts of Brunswick black with one of white, red, or colored paint, the body of which is composed of red or white lead or litharge. Red lead is the best for many reasons, if finely ground and thoroughly mixed with linseed oil; any of several kinds of bitumen may be used, either natural mineral asphalt, pine pitch, or artificial asphalt, such as gas tar or the residuum of petroleum distillation in cases where the crude oil has been distilled before being treated with acid. This gives a very hard, bright pitch, which is soluble in "one run" paraffin spirits, and which makes the base of an excellent, cheap, and durable paint for ironwork in exposed positions.

During the past few years we have heard many accounts of the preservative influence of paraffin when applied to iron surfaces, and can be recommended for all cases of ironwork which can be treated hot. The most effective, if not the most practical method of applying it is to heat the iron in vacuo, when paraffin, raised to the proper temperature, is run upon it. By this means the iron is claimed to be penetrated to a sufficient depth to afford a very effectual protection against oxidation, especially when a suitable paint is subsequently applied. Any non-oxidizable substance would probably answer, but paraffin is as cheap as any and quite as good, if not better. Brushed upon the outside merely, it is doubtful if paraffin would have much effect in preserving iron, while it would certainly lead to lessen, if not destroy, the mechanical adherence of a surface paint.

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