Brick Fireplaces

For openings up to three feet or thereabouts, a relieving arch of a single ring of half-bricks is all that is required; but for larger openings, several rings may be used.

Fig. 104 shows an arch of three rings, and it will be noticed that each arch is separate and not bonded into its fellows. It will also be noticed that the bricks of these rough relieving arches are not cut taper, and thus the joints are slightly more open on the back of the arch than on the under side. In making drawings of such arches, the draftsman draws a ring around the center from which the arch is struck, the diameter of the ring being the thickness of the brick. This thickness is then stepped off on the under side (soffit) of the arch with a pair of dividers, and the straight edge placed against the ring and one of the divisions on the soffit (see A).

How to Lay Out Arches. The chief problems, however, with which the practical layer-out of arches is confronted, arise in connection with the modern use of fine pressed brick for so many first-class structures. For while the mere curve is sufficient for practical purposes in rough relieving arches, the arch made of facing bricks, and forming a feature of some fine front, must be set out exactly for the purpose of cutting and fitting, or perhaps molding, the bricks of which it is to be composed. Brick arches in which the bricks have been specially cut or molded are generally termed gauged_ arches, and are frequently used nowadays.

The radius of the arch is scarcely ever given by the architect, the rise being almost invariably denoted instead. The writer has before him an elevation of a brick-fronted building with some eight or ten openings of varying widths, but the same rise is specified for all the arches over them. This means that the layer-out has to find the centers of the several curves from the given particulars of their rise and span. This he does as shown iu Fig. 105, the first being the geometrical method of the drafting room; the second, the practical method of the laying-out shop. In both cases, the center from which the arch is struck is found at the intersection of the lines drawn from the center of each half of the arch.

As the bricks in gauged arches are used full length, the thickness of the brick is marked off around the back of the arch, and the joints drawn to the center, as in Fig. 108, at left. The joints

arc very fine, being usually specified to be not more than IA inch, the mortar being either of fine cement or lime putty. In Europe, special bricks are made for such arches, and are known as red rubbers. When new, they are quite soft, and can be sawed with a handsaw, and rubbed upon a block with sand and water to form close joints. After being exposed to the air for a time, the surface of these bricks becomes exceedingly hard and impervious to the action of the weather. For the red brick dwellings of "Queen Anne" and "Colonial" style, now so much in vogue again, such bricks are exceedingly useful. Not only can they be cut for the characteristic flat arches of these styles, but moldings can be worked on the angles, and panels formed to relieve broad surfaces of wall. More often, however, bricks for gauged arches are specially molded to the builder's drawings by the makers of the face bricks, with fairly good results in the finished work.

The flat arch just referred to is also much used in brick fronts in city buildings, and is drawn as shown in Fig. 108, at right. It presents no difficulty to the layer-out, the joints being found by making a curve above the arch and stepping off the thickness of the bricks upon it.

There is one important point to be remembered, though, in building such arches — namely, that a perfectly, straight soffit will always appear to be sagging. The remedy for this is to allow a trifling rise—say 1/2 inch for every three feet of span—which will be sufficient to make the under side of a flat arch look straight. This can be easily done on the job by laying two strips tapering from nothing at the ends to the required allowance at the middle, upon the support or centering upon which the mason forms his arch.

Of course, flat arches are not very desirable, from a structural standpoint, and should not be used for spans more than 4 or 5 feet at the outside. Occasionally, for the sake of uniformity, a flat arch is used over a larger opening, perhaps a broad window or doorway; but in such eases the weight of the superstructure is carried on iron girders, and the brick arch is only a sham or casing toward the street.