PAINTING TIN ROOFS The painting of tin roofs is closely allied to the painting of galvanized iron, because roofing tin is composed of thin sheets of iron coated with a mixture of tin and lead. Many tin roofs are painted with cheap metallic paints, mixed with substitute or so-called "paint oils" made largely from rosin and petroleum products. The paint is but a thin wash at best, and the protection afforded by it practically nothing—if not worse than useless.
To make the paint of real value the tin roof should be painted with the same care as the rest of the building. It is, first of all, essential that the tin should have at least one coat of paint upon the under side—two coats are far better— before it is laid upon the roof. The reason for this is that there is always more or less conden sation on the under side of every tin roof, and the moisture deposited upon the metal will in evitably cause rusting unless there is an ade quate protective coating of waterproof paint. This painting should be done after the tin has been soldered together in long strips ready to be put on the roof, and the paint should then be allowed to become thoroughly dry before the roof is laid.
In making tin plate the sheets are dipped into palm oil, which renders painting difficult. To get rid of the palm oil, sponge off the roof with benzine.
Opinion varies somewhat as to what is the best paint for a tin roof, but it seems to be pretty well settled that either Prince's mineral brown or a first-quality silica—graphite paint—will give satisfaction. The oil should be more elastic than for painting woodwork, since the expan sion and contraction of a tin roof with heat and cold are factors that must be reckoned with. For this reason either a genuine kettle-boiled linseed oil should be used, or, if raw oil is employed, enough fish oil or other non-drying oil should be added to render it elastic, though it should neither be tacky nor so non-drying as to wash off.