The Process of Slating.
When the blocks of slate for roofing have been split, and the laminæ roughly squared, they are sorted, according to their size and quality, and are brought to market under the quaint names of Imperial slates, Duchesses, Countesses, &c., the first variety being the largest. The best roofing-slates come from the celebrated vale of Festiniog.
Slates are laid on battens, or thin narrow deal boards, which are nailed horizontally on the common rafters of the roof, at equal distances apart, which distance is governed by the size of the slate to be employed. An entire board is nailed along the lowest edge of the roof to receive the lead of the gutters, which are first laid, and then the lowest course of slates are nailed and pinned down to the lowermost batten; so that two-thirds the length of the slate, at least, shall lie over the lead. The next course of slates is then fixed, so that every slate shall overlap two-thirds the depth of the course below it, every slate being also laid over the joint, between two slates of that undercourse. By this construction the rain that runs through the joint between any two slates is kept from penetrating into the roof by being received on the surface of the slate beneath that joint; and the bottom course of slates is double, to continue the same principle down to the lead gutter.
The slates are fixed to the battens by two copper nails and a wooden pin when the work is well executed; holes being picked through each slate for the nails to pass through.