Lead is a material of a soft, heavy, highly fusible, and extremely flexible nature, used as a covering to flat roofs, and as a means of rendering slated and tiled roofs watertight; being, on account of its flexibility, highly adapted for all angular and similar joints in roofs, where the brittle nature of tiles and slates renders them useless. It has no strength whatever, and is the product of an ore which is smelted down to a molten state, and rolled into large sheets, or made into pipes and cast-pigs which are beyond the province of this chapter.
The sheets may be either cast or milled, the former being heavier in weight, thicker, and harder; but, on account of its irregularity in thickness and liability to flaws and sandholes in the casting, it is of little service to the plumber, except in very heavy work and the covering of exceptional church roofs.
Milled lead is rolled out, as the name implies, into thinner sheets of a more uniform thickness and denser nature, and it is in this form that lead is mostly used by the builder or plumber for roof-coverings and similar work, in which it can be " bossed " up as required. Its quality is described by its weight per superficial foot, the qualities most used being 4, 5, 6, 7, and 8 lbs. per foot in weight; and, to give the student an approximate idea of its thickness, it may be mentioned that 7 lbs. milled sheet lead is a little under and 8 lbs. a little over 1/8 inch in thickness.
Except in very exposed positions the following weights are suitable, and generally used for the nature of work specified: 4-lb. for soakers; 5-lb. for flashings; 6-lb. for valleys; and 7-lb. for gutters, flats, hips, and ridges.
It should always be borne in mind that the sun has great power over lead, drawing it away, as it were, so that leadwork should never be securely fixed, but always free to move. Before proceeding to enter fully into the details of the various positions in which lead is used it will be advantageous to enable the different parts to be identified on a roof plan.