This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
When the mortar is ready for putting on the laths, we must see that the first or scratch coat is well trowelled to push it through the spaces between the laths so as to form a good key. In ordinary two-coat work this first coat is put on thick enough to come within an eighth of an inch or less of the face of the grounds and beads, as the finish or skim coat is merely a thin veneer of lime putty and fine white sand, trowelled and brushed to a hard surface. In three-coat work, the first coat is put on about one-quarter of an inch thick and when somewhat hard it is scratched with diagonal lines nearly through to the laths. As soon as this coat is dry, the second coat is applied and brought to a plane with all angles and corners true and plumb. On large surfaces or important work this is best done by running "screeds", which are strips of mortar six to eight inches wide and three or four feet apart, carefully laid and levelled and plumbed with corners and angles made true and brought to the line of the second coat, which is filled in between these upon the scratch coat and brought to a line by running straight edges from screed to screed. Upon this second coat is applied the third or finishing coat, usually either the skim coat as upon two-coat work, or a "white-coat" which is made by mixing plaster of paris and marble dust with the lime putty. If a rougher finish is desired, as for frescoing, a coarse sand in greater quantities may be mixed with the lime putty and floated with a pine or cork-faced float. By consulting the specifications we find that this finish is called for in two-coat work to be left "medium rough."
Before the plastering is begun the windows must be closed in with screens made of cotton cloth tacked upon wooden frames, made to fit the window frames. These are not only to protect the plastering from freezing, by which ordinary lime mortar is completely ruined, but also to prevent unequal drying of the finished walls which will occur near the windows in good breezy weather.
The plastering of exterior walls is done to a large extent in Canada and the British possessions and is used to increasing extent in the United States. This is best done over matched boarding by furring off with seven-eighths inch strips and using wire or other metal lathing which later events have shown is better if galvanized or painted. The plastering should be three-coat work, with one-third of Portland cement for all three coats, the last having the coarse sand or gravel if a rough finish is desired. If metal lathing is not easily procured a good result is obtained by lathing upon the boarding diagonally in one-and-one-half inch spaces and repeating the lathing diagonally in the opposite direction, all well nailed and secure. Upon this we may plaster as upon the metal lathing.
EXTERIORS OF RESIDENCE FOR DR. GRAFTON MUNROE.
FIRST AND SECOND FLOOR PLANS OF RESIDENCE FOR DR. GRAFTON MUNROE.
Frank Chouteau Brown, Architect, Boston, Mass. Exteriors Shown on Opposite Page.