This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
Roofing felt is a substance composed largely of hair saturated with an asphalte composition, and should be chosen more for closeness of texture than excessive thicknesa It is sold in rolls 2 ft. 8 in. wide and 25 yd. long, thus containing 200 ft. super in a roll. Before the felt is laid on the boards (3/4-in. close boarding), a coating composed of 5 1b. ground whiting and 1 gal. coal tar, boiled to expel the water, is applied, while still slightly warm, on the boards themselves; the felt is then laid on, taking care to stretch it smooth and tight, and the outside edge is nailed closely with 7/8-in. zinc or tinned tacks. The second width of felt laps the first 1 in. at least, the joint receiving a little of the composition, and the tacks pass through both thicknesses of felt, and so on till the whole of the roof is covered. Then the surface requires a coat of the composition, and in 3 or 4 weeks a second or finishing coat, when it will need nothing for 3 or 4 years, but should receive one the moment it begins to bleach. The gutters and ridge are generally in 2 thicknesses of felt. A dry day should be selected for the work.