This section is from the book "The Principles And Practice Of Modern House-Construction", by G. Lister Sutcliffe. Also available from Amazon: How Your House Works: A Visual Guide to Understanding & Maintaining Your Home.
Fig. 69 - Plan and Elevation of Recess for Dog.grate.
A. Sitting-room fireplace. B, bedroom fireplace; C, smoke-receivers; D, smoke flues lined with fire-clay tubes: K, solid concrete hearth; F. fender wall; G, fender curb; a, tiled hearths; I. brick trimmers arch; J, trimming Joists; K, trimmers.
Many of the glazed-ware mantels and fireplaces are made to fit the ordinary fireplace opening shown in Fig. 70, but for some of these a special arrangement of the back hearth is required, as shown in Fig. 71, which is a section of the "Rational" fireplace, - a fireplace which several advantages, but which necessitates care in the construction of the hearth when used in connection with wood floors, as great heat is developed under the hearth.
In order to avoid the danger of fire, the brickwork at the back of a fireplace ought to be at least 9 inches thick. When the back is only 4½ inches thick, wood plugs, driven into the joints of the brickwork to secure the skirting on the other side of the wall, may penetrate to the flue, knocking off the pargeting and leaving the wood exposed to the heat of the fire-back. It is particularly necessary to bear this warning in mind when slow-combustion grates are used, as these develop great heat in the back and sides of the fire-receptacle.
Great care must also be taken that wood floor-joists and roof-timbers are not allowed to enter the brickwork of flues and fireplaces. The trimming of the floor-joists in front of a chimney-breast is now never entirely neglected, but it is equally necessary that the joists bearing at the back of the breast should also be trimmed, as illustrated in the section in Fig. 70. Corbels should be provided for the ends of roof-timbers near flues.
Wood mantel-pieces are also a source of danger. In my own office I was one day surprised by a smell of burning paint and wood, and found that a live coal falling on the hearth had set fire to a piece of paper, and this in turn had set fire to the woodwork of the mantel Care should be taken that all wood is removed from the metal of the grate by means of tiles or marble slips, the further the better; a glazed-ware fender curb, with the woodwork (if any) extending to the floor outside the curb, is safer than a movable fender.
Wood mantel-pieces, besides being a source of danger from fire, may prove unsightly in consequence of warping and shrinking. To prevent this unsightliness the wood must be of the best, and the mantel must not be delivered at the building for some weeks after the plastering has been completed; indeed, the dampness of the walls is more often at fault than the quality of the wood. Painting the back of the woodwork reduces the amount of absorption from the walls, and, therefore, may prevent warping.
Fig 71. Section of the "Rational " Fireplace.
The faulty construetion of hearths is probably the cause of more household fires than any other defect When the hearth rests on the solid ground or on the ground-layer of concrete, or when the floor is formed entirely of concrete or other fire -resisting materials, the hearth cannot well be a source of danger; when, however, the floor is constructed of wood joists and boards, danger is inevitably present Until recent years the visible portion of a hearth was usually of flagstone in two pieces, known respectively as the "front" and "beck" hearth. The beck hearth rested on the brickwork of the chimney-breast beneath, while, in jerry-buildings, the front hearth was carried by fillets nailed to the trimmer and trimming joists, or by shallow wood joists extending across the trimmed space. An example of this kind came under my own observation some years ago; the hot ashes from the fire above, passing through the joint between the front and back hearth, twice set fire to the pitch-pine ceiling below. Fortunately in neither was very much damage done, but sufficient at any rate to have paid a dozen times over for the construction of a proper hearth when the building was erected. After the second fire the hearth was bedded on concrete, and no further damage has been done.
Sometimes a counterfloor is constructed under the hearth with shallow wood joist- and boards, and covered with mortar or fine concrete, on which the hearth, whether of stone or tiles, is bedded. This is an improvement on the method previously described, but it is not entirely satisfactory. A better and more general form of construction is delineated in Fig. 70, p. 130, a trimmer-arch of brick, marked I, being turned from a skewback cut in the chimney-breast to the trimmer, and the space above being filled with cement-mortar or fine concrete, floated to receive the hearth-tiles. A more recent invention consists of a curved iron or steel plate fixed to the trimmer and wall, and covered with concrete, as illustrated in Fig. 72. The plates are made 1 foot 3 inches, 1 foot 6 inches, and 2 feet long, and with a span of 1 foot 2 inches and 1 foot 6 inches.
Fig. 72 - Moore's patent Hearth-boxing.
Concrete alone is sometimes used, fillets being nailed to the trimmer and trimming joists, and a chase being cut or formed in the brickwork to support it. The concrete is deposited on a temporary platform of wood, which is allowed to remain in position for a fortnight or more (till the concrete is sufficiently hard), and is then removed.
Hearths in all rooms of any importance are now finished with tiles, which are laid in cement on the floated surface of the concrete below.
The construction of hearths in boarded rooms on the ground-floor is an easy matter. A fender wall of brick is usually built up to the edges of the hearth, and on it the floor-joists rest, as shown in figs. 69 and 70. The space under the hearth is filled with concrete.
Glazed fender-curbs of various sizes, colours, and designs are now made, and are frequently used in place of movable metal fenders. They are shown in several of the foregoing illustrations. The ends of the curbs should be ground perfectly true, and secured to each other with dowels, the whole curb being bedded in cement-mortar. It is best to make the concrete hearth large enough to receive the curb; where this is not done, a chase ½ inch deep should be cut in the floor-boards, and clout-nails driven, not quite to the head, in order to afford a key for the cement-mortar.