Certain precautions, however, must always be observed in winter painting. One of these is to be very careful that the surface to be painted is perfectly dry and absolutely free from small particles of ice or frost. During winter nights whatever moisture may be con tained in the air is very apt to be deposited upon the surface of the weatherboards, freezing there to form a thin film of ice or frost, often so light as to be almost imperceptible. But this ice film will be sufficient to prevent adhesion of the paint to the wood. After the sun has been up for some time, this coating of frost gradually dis appears, being absorbed by the atmosphere, whose capacity for holding moisture is increased as the temperature rises. Even a few degrees makes a very considerable difference. The painter should therefore wait until all trace of frost or moisture has disappeared, even though he may not be able to begin work until nine or ten o'clock; and he should stop work as soon as the sun gets so far down in the west as to cause the frost again to deposit on the surface. With the precautions mentioned, winter paint ing is fully as durable as painting done at any other season of the year. Besides, there are no insects or dust to cause damage to the fresh paint.
Another precaution is to avoid paints con taining any considerable percentage of water when winter painting is being done. Some of the mixed paints now on the market contain from fifteen to twenty per cent of water in the thinners; and while this water may not be detri mental if the paint be employed at ordinary temperatures, yet there is danger that this water will freeze when painting is done in win ter, causing the paint to disintegrate rapidly.
Painting a Tin Roof. When winter is com ing on, the tin roof should be carefully looked over. It is a very wise old proverb that "an ounce of prevention is worth a pound of cure," and it costs a good deal less to have the roof painted and any leaks stopped before the snow renders it impossible, than to repair plastered ceilings and repaper walls damaged by leaky roofs. A tin roof should always be thoroughly painted on the under side—preferably with two coats, though it seldom gets more than one, and a scant one at that—before the tin is laid on the roof. It is surprising what a large quantity of moisture from condensation will collect on the under surface of a tin roof; this will sooner or later start rust, and, once the rust begins, it will go on increasing until the roof is riddled with holes.
As the sheets of tin are dipped in palm oil after they have been coated with the mixture of lead and tin into which the iron sheets are dipped to produce terne roofing plate, and as this palm oil is repellant to paint, many roofers and painters have advocated allowing the tin to stand until it begins to rust a little in order to give the paint a good hold. But while the paint may cling better to a rusted tin roof, it will not prevent the rust from growing under neath the paint. Once let rust start, and it acts as its own oxidizing agent, spreading under neath any protective coating that may be ap plied over it. The proper plan is to wash the tin carefully and thoroughly with benzine, as soon as the roof has been covered. This will
remove not only the traces of palm oil left on the surface of the metal, but also the rosin and soldering fluid left by the tinners in making the joints. Besides, as the benzine evaporates com pletely, it will leave no trace upon the surface of the tin roof, which can be painted upon as soon as it is dry.
Experience has proved that white lead does not make a good priming paint for tin roofs or for iron work. Being composed of the hydrate as well as the carbonate of lead, it con tains within itself rust-producing agencies. Red lead is recommended by some, but is diffi cult to apply. To be properly used it should be brought to the job dry, mixed with linseed oil on the spot, and the painting should be done as soon as it is mixed. The great weight of red lead causes it to settle in the pot; and unless it is kept constantly stirred, and the painter is more than usually careful, the paint film will be very uneven, thick in some places, but in ether places little more than a colored wash.
A tin roof is exposed to great variations of temperature, and whatever paint is used should be sufficiently elastic to withstand the expan sion and contraction that are constantly taking place. The experience of painters generally is that the best paints for a tin roof red, mineral brown, and graphite, and that the oil should be boiled linseed oil, or half boiled and half raw oil, or raw linseed oil with a suffi cient percentage of fish oil to make the paint film elastic. By boiled oil we mean genuine kettle-boiled linseed oil and not raw oil "doped" with so large a proportion of liquid driers that its life will speedily be burned out of it. Boiled oil dries rapidly on the surface, while under neath it always remains more or less tacky. This property is very detrimental to ordinary paint, and boiled oil should usually be avoided on account of its tendency to alligator and blister. But on a tin roof this tackiness is an advantage because the paint film is better able to expand and contract with the metal.
In choosing the pigment, be very careful to avoid the cheap metallic paints made from the spent pyrites from sulphuric acid works or the refuse from iron furnaces where certain low grade ores containing sulphur are worked. These paints contain more or less free sulphur ous acid, and while they may be good enough for painting barns or box cars, where the sulphur will work no harm, they will probably cause a great deal of damage to the tin roof, because every rain will cause some of the sulphurous acid to turn to sulphuric acid, which will soon eat holes in the roof. Many instances are on record of tin roofs that have been eaten through in less than a year by these low-grade metallic paints. The safest iron oxide paint to use (other than the expensive Venetian red) is the well-known Prince's mineral brown. This is made from an iron ore which is remarkably free from sulphur and which is roasted to drive off any combined water. Excellent results can also be obtained by the use of a first-class graphite paint, where the color of this material is not objectionable.