This section is from the book "Modern Buildings, Their Planning, Construction And Equipment Vol1", by G. A. T. Middleton. Also available from Amazon: Modern Buildings.
In slating, the work is always commenced at the eaves or lowest edge of a roof by laying a row of special cut small slates, called a Doubling Course. The length of the slate in this course is determined by adding the lap plus 1 inch to the gauge. Thus in Fig. 288 the length of the doubling course is 6 + 3 + 1 = 10 inches.
The lower edge of the doubling course is tilted either by means of the facia board, as in Fig. 288, or by means of a Tilting Fillet, as in Fig. 289, so as to make its edge fit more closely against that of the next course of slates above.
When battens are used, the lowest one should be placed with its centre at a distance equal to the length of the doubling course minus 2 inches, - 1 inch being allowed above the nail-holes and 1 inch for the slates to overhang the tilting fillet above its lower edge. Thus in Fig. 289 the centre of the first batten is 10-2 = 8 inches above the outer edge of the facia board.
When a slated roof ends with a verge, or dies against a gable wall, the slates have to be cut to fit. This may be done, as shown at A, Fig. 290, by cutting slates of the size used for the rest of the roof, or, as at B in the same Figure, by cutting larger sized slates. The latter method, needless to say, is preferable.
The under side of verges should be pointed.
When a slate roof dies against a gable wall a cement fillet is sometimes formed at the junction to keep out the rain, but lead flashings, as described in a later Chapter, make a more watertight joint.
The slates have to be cut to fit at the ridge and hips of a roof, and the angles between the different planes of the roof are covered either by means of a slate ridge piece, as shown in Fig. 292, or by means of tiles made for this purpose, thoroughly bedded in hair mortar. Slate ridge pieces are often made in two pieces, one of which is holed and screwed to the ridge board by means of copper screws, the holes being stuffed with white lead, while the other fits over the first.
The junctions of hips and ridges are usually covered by means of a specially made tile, and when a ridge terminates in a verge special finial tiles are frequently used.
Lead is also used for making ridges and hips watertight.
When slates become broken they are removed, the nails being cut away or drawn by means of a ripper - an iron instrument about 2 feet long, with a handle at one end and a thin blade terminating in a broad end, of the shape shown in Fig. 293. The indentations in the edge of the broad end are for catching the shank of the nail to be cut.
Fig. 293. Ripper.
Strips of lead or copper, called Tacks, are now hooked over the head of the slate beneath the space to be repaired, and a new slate is slipped into position, where it is kept by turning the lower ends of the tacks over the tail of the new slate, two tacks being used for each slate.
Stones that can be split into slabs of from 1/2 to 1 inch in thickness are also used for roof coverings. Such stones come from the limestone quarries of Colly Weston, Northamptonshire; Stonefield, Oxfordshire, and Naunton, Gloucestershire. These stones are supplied in odd sizes up to about 2 feet square, and must be sorted before use, the longer slabs being used at the eaves. The courses should diminish in size towards the ridge, the battens upon which they are laid being fixed to the diminishing gauge. Laths are nailed to the rafters between the battens, and the space between the battens filled up with stone lime mortar, preferably made from the same limestone as the slabs (see Fig. 294). The slabs are then laid, commencing from the eaves as in ordinary slating, one nail being inserted at the head of each slab, which should be thoroughly bedded in lime mortar. The joints of the slabs are pointed in lime mortar as the work proceeds.
The nails for securing slates to the boards or battens have flat circular heads large enough to overlap the holes, and are made of iron, copper, zinc, composition, or lead.
Iron nails are made of either cast or malleable iron. Cast-iron nails resist oxidation well, but are brittle and snap easily. Malleable iron nails are usually galvanised or painted to resist oxidation.
Copper nails resist oxidation well, are expensive, and are therefore not used to any great extent.
Zinc nails are very soft, and consequently difficult to drive.
Composition nails, made of an alloy of tin, copper, and zinc, are hard enough to permit proper driving and resist oxidation.
Long lead nails are used chiefly with iron battens, being placed through the holes in the slates and bent round the battens.
The edges of slates are trimmed by means of a tool called a zax, Fig. 293; the slate being laid over an iron straight edge or cutting iron, which is fixed to the edge of a bench. The slate to be cut is laid across the cutting iron and a few smart blows with the sharp edge of the zax cuts the slate to a straight edge. A sharp point is formed on the back of the zax for holing. A metal square is used for testing the squareness of the slates. The nails for slates are driven by means of a Slater's Hammer, which is provided with a sharp point at one end for holing, while at the side is a claw for removing broken or bent nails.
Fig. 293 also shows a Ripper, which is used, as already explained, for repairing work.