This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
A string-course cornice, or store cornice as it is often called because it is so commonly used over store fronts, is shown in Fig. 15. The lookouts are made of band iron 1/4 in. X 1 1/2 in. and are tied into the brickwork at a and b, these ends being built into the wall. The lower ends of the lookout frames are continued down over the face of the beams and along under their lower flanges, and are then bent up at the back, as shown at c. An angle iron at d running the whole length of the cornice is bolted to the ends as shown at c and keeps them in place. A sloping platform of matched boards is screwed on the top of the lookouts. The sheet-metal work is bolted to the band iron in the usual manner, a soldered double seam with cleats is made at e, and the top covering enters the wall at f. An iron plate, either plain or ornamental, is usually secured at g to form the soffit of the beams over the opening.
After the beams are set on their columns, and before the mason begins to build on them, the cornice must be set in position. The cornice being set true and level, the mason finishes the wall up to the course h; then the flashing is put on, the top edge f being bent over about 3 or 4 inches, as shown. When this is finished the mason proceeds to build the superstructure. If the wall is built before the cornice lookouts are ready, the anchors a and b must pass through the wall and be bent over at the back, and the flashing f must be let into the raglet and be batted with lead, the rag-let being filled with mastic or other cement in the usual manner.
24. In many cases it is advisable to make the lookouts of cast iron instead of wrought iron, as, for example, when a very large number of small lookouts having the same shape are required. If the molding is small and extends as a belt, or string, course around the building, it is certainly advisable to use cast-iron lookouts. The chief advantages of cast-iron lookouts are accuracy in the lines of the cornice, economy in construction, and durability.
Accuracy is insured when the lookouts are properly lined up, because each lookout is a duplicate of the others, they being all cast from the same pattern. Economy of construction lies in the fact that the labor of making the lookouts and of fitting the sheet metal to them is reduced to a minimum. And the durability lies in the fact that cast iron is less corrosive than wrought iron. Iron lookouts should always be coated with asphalt or other protective covering in order to prevent rapid corrosion.
25. Galvanized iron should never be used for cornices except in the very cheapest work, and even then it should be thoroughly painted on both sides. Sheet copper (cold rolled) is preferable, however, in every case. The metal itself costs considerably more than iron, but the labor and other expenses, relative to its construction and installation, are about the same.
26. Copper cornice work does not require to be painted for protection. It is, in fact, better practice to leave the metal thoroughly scoured, clean, and uncovered, and allow the weather to slowly change its color. Copper sheet-metal work has naturally a dark-green tint, but it often takes a very long time to get that color. The time required will depend considerably upon the climate, the weather, and the composition of the atmosphere. Where the rain becomes acidified, by falling through air charged with sulphurous gases, the color changes rapidly, but where it falls pure and clear, the copper changes color very slowly.
When it is desired to hasten the color it is customary to produce an artificial color by washing the copper with acids. One method is to thoroughly scour all the copper work to remove any grease or acid spots, then wash the entire surface with a solution composed of 1 pound of sal ammoniac to 5 gallons of water. This solution should stand about 24 hours before it is applied. After the copper has been uniformly covered with the solution, it should be allowed to stand for a day or two and should then be lightly sprinkled with clean water. If the water is put on too freely, it will run in streaks. After a few days the copper work should have a beautiful and uniform greenish-brown color which will stand the weather. The same effect may be produced by using vinegar and salt in the proportion of 1/2 pound of salt to about 2 gallons of vinegar.