How this was done is best expressed in the claim granted the patentee, copied from the United States Official Gazette:
“A metal roofing plate having a gutter formed by corrugations at one side, and a perforated flange at the side of the gutter, whereby it shall be nailed to the roof of a house; a broad corrugation at the other side adapted to form a seam with the adjoining edge of a corresponding plate, substantially as shown and described.”
The advantage of this lock is that it makes a water-tight seam without soldering or hammering down. The plates are joined as easy as crossing two sticks, with ample provision for expansion and contraction. This lock is the perfection of simplicity; there is no exposed seam where water is liable to lodge and cause rust; no cleats are used, and no tin springs are necessary to hold the side edges of connecting plates to prevent water seeping through.
PAINTING SHEET-METAL ROOFS.
The subject of painting sheet-metal roofs is one of great importance, says the Builder, Decorator and Wood-Worker, not only on account of the protection afforded, but because the material, when properly colored, can be made pleasant to the eye when placed in exposed positions. While many kinds of paint have been discovered and patented, composed of a great variety of materials, it is a question if there is a substance used that is an effective substitute for linseed oil, regarding the effectiveness of which an authority on the subject says: “By consulting experienced and unbiased painters you will learn the fact that there is no vehicle pigments at all approaching linseed oil in effectiveness and durability, especially for exposure to the weather. A good paint must be both hard and elastic. It requires hardness to prevent abrasion and wear, and elasticity to prevent cracking from expansion and contraction. Nothing but linseed oil will give these qualities, for, strange as it may seem to many in these days of novelties, the pigments really add but very little to the effectiveness of paints. Mark, we say the best of pigments, for many pigments are the reverse of protective, and are really destructive to both the vehicles and the material which they are supposed to protect. For example, coal tar and all its products, whether called dead oil, asphalt, rubber, etc., are of the class just described, and their use at any price, especially for covering sheet-metals, is a wanton waste of money. Extended experiments have demonstrated that there is no better pigment for metal than a good iron ore ground to an impalpable powder. To be most thoroughly effective the pigment must be intimately incorporated with the vehicle, which can best be done only by grinding them together in a stone mill by steam power.” It is of the greatest importance that sheet-metal roofs, especially those made of iron, should be protected from the action of the elements, as when so protected there is hardly any limit to the time they will last. In order that the paint should be effective, it should be applied before the iron has had an opportunity to rust, and the first coat should be of the best quality and applied in the best manner; or if it is defective it is plain that it will not only require repainting far sooner than it should, but no matter how good the subsequent coatings of paint are, they cannot be effective if founded on an original coating which has commenced to crack or peel, as it certainly will if not prepared with the best methods and materials. Another important point to be observed in the painting of sheet-metal is that the paint should not be too thick, as it is the linseed oil that is to be depended on to furnish protection, and as the action of the air on the surface of the exposed oil gives it a particularly hard surface, two thin coats of paint are much more durable than one thick one.
Remember, it is the rust-preventing qualities of linseed oil, combined with the oxide of iron, that makes steel or iron sheets resist the corrosive action of oxygen, which is ever present in the atmosphere. ([See page 101.])