The upper floors of buildings are made fire-proof in a similar manner, and for this purpose there are several excellent patented methods. The iron girders are closed up by brick arches, or filled between with concrete. The only objection to this mode of construction for upper floors is the great weight, and the walls require to be made of extra strength. Several years ago a hollow brick was used to form such arches and roofing, e.g., the dome of the Rotunda, at the Bank of England, is formed with them. The brick is somewhat similar to a flowerpot, but flat and closed at each end. There were several varieties of these cone bricks, as they were called; a few are preserved in the Soane Museum. One sort was 7½ inches in height, 4⅛ by 2⅜ inches at the top, and 3-2/8 by 2 inches at the bottom. They were curved inwards with a small opening, 1 by 2/8 inch in the centre. The edges of the brick were slightly splayed, and the sides scored; these were as strong as the common bricks, and very much lighter. When the East India House was pulled down a large quantity of these bricks was obtained; they were brought to Kensington, and the builders did not know what they were intended for; their purpose being pointed out, they were used up in the construction of fire-proof flooring.
Fire-proofing.—A method of rendering buildings nearly fire-proof was introduced about 1770 by Mr. David Hartley, M.P. for Hull. It consisted in placing thin metal plates between the flooring boards and the joists, so as to prevent any upward currents of air. For domestic buildings the system was one of great value. After several successful trials it obtained considerable notoriety, and being thought capable of an impossibility, that of rendering a Theatre fireproof, it was applied to the Pantheon Theatre in Oxford Street. On that structure being burnt to the ground the plates lost their character, and went out of use. It was clearly a mistake to apply them to such a building. Thin iron plates hung at a short distance below the ceiling were successfully adopted by Mr. Walter Crum, to prevent the spread of fire from one room to another in his calico printing works, near Glasgow.
Damp.—The damp rising from foundations is more easily guarded against than damp coming against a building laterally. Houses in exposed situations and subject to driving winds, are often very wet inside the walls, the rain being driven through them. Sometimes the best construction will not keep out wet. As a rule, a well-built wall wherein proper material has been used, should not be damp.
A rectory, not far from Salisbury, where the author was engaged a few years ago, was in such an exposed situation that on three of its sides no tree or any other object in a direct line could be seen for three miles. Clothes, if placed against the external wall of the dressing-room, were often quite wet. The Rector had tried several preventives himself; one was a mixture, used to water-proof cloth—a wash of soap and alum.
The ingredients were mixed in the following proportions: ¾ lb. of mottled soap to 1 gallon of water. This mixture, when in a boiling state, was laid over the surface of the brickwork steadily and carefully with a large flat brush, so as not to form a froth or lather on the surface, and was permitted to remain twenty-four hours to become dry and hard. Another mixture was then made in these proportions: ½ lb. of alum to 4 gallons of water, which, after standing twelve hours, in order that the alum should be completely dissolved, was applied in like manner with a flat brush over the coating of soap. The coating had to be very often renewed. The wall most exposed was made free from wet by being covered with a coating of cement.
Walls exposed to damp should be coated with a thin layer of Portland cement, mixed with a little plaster of Paris, and after this is thoroughly dry, it may be hardened and rendered impervious to water by painting it with boiled linseed oil and red lead, mixed together.
In very exposed situations all external walls should be battened, lath and plastered within, or built with a hollow cavity in the middle, with proper bond and a proportionate increase of thickness,—the hollow could be filled with concrete, or the back of the bricks covered with pitch. There are several other methods for keeping walls free from damp. One is to saturate the walls with some kind of mastic, or a wash composed of two or three parts of resin and one part of drying oil, to the extent of as many washes as the wall will absorb. This must be quite dry at the time, or be dried by means of a small portable furnace. The plan is effectual, but it is a difficult operation to perform. A cement composed of lime, boiled linseed oil, white lead, and sand, has been recommended.
Besides these various compositions, there are several excellent well-known paint and metallic cements, which have stood very severe tests, and are largely made use of; but walls properly constructed should not require their application.
Plaster ornament for a ceiling.