353. This is generally either rough-cast or stucco. The first is a description of coarse plastering, generally applied on laths; the second is a description of plastering on brickwork, executed so as to resemble stone ashlar.
Rough-cast has been extensively used in Canada, and to some extent in the Northern States. It is said to be much warmer than siding or shingles, less expensive, and quite as durable. It is also more fire-resisting.
"There are frame cottages near the city of Toronto and along the northern shores of Lake Ontario that were plastered and rough-casted exteriorly over forty years ago, and the mortar to-day is as good and sound as when first put on, and it looks as though it was good for many years yet if the timbers of the building it preserves remain good.
"It is quite a common occurrence in Manitoba and the northwest Territories in the winter to find the mercury frozen, yet this intensity of frost does not seem to affect the rough-casting in the least, though it will chip bricks, contract and expand timber and render stone as brittle as glass in many cases."*
Frame buildings to be rough-casted should be covered with sheathing and one thickness of tarred paper. The partitions should be put in and even lathed before the outside is plastered, as it is important to have the building stiff and well braced.
The best mode of rough-casting, as practiced in the lake district of Ontario, is said to be as follows :
Lath over the sheathing (or tarred paper if used) diagonally with No. I pine laths, keeping 1½ inches space between the lath; nail each lath with five nails and break joints every 18 inches; over this lath diagonally in the opposite direction, keeping the same space between the laths and breaking joint as before. Careful and solid nailing is required for this layer of lathing, as the permanency of the work depends to some extent on this portion of it being honestly done. The first coat should consist of rich lime mortar, with a large proportion of cow's hair, and should be mixed at least four days before using. The operator must see to it that the mortar be well pressed into the key or interstices of the lathing to make it hold good. The face of the work must be well scratched to form a key for the second coat, which must not be put on before the first or scratch coat is dry. The mortar for the second coat is made the same as for the first coat, and is applied in a similar manner, with the exception that the scratch coat must be well damped before the second coat is put on, in order to keep the second coat moist and soft until the dash or rough-cast is thrown on.
The dash, as it is called, is composed of fine gravel, clean washed from all earthy particles and mixed with pure lime and water till the whole is of a semi-fluid consistency. This is mixed in a shallow tub or pail and is thrown upon the plastered wall with a wooden float about 5 or 6 inches square. While the plasterer throws on the rough-cast with the float in his right hand, he holds in his left a common whitewash brush, which he dips into the dash and then brushes over the mortar and rough-cast, which gives them, when finished, a regular uniform color and appearance.
For 100 yards of rough casting, done as above described, the following quantities will be required : 1,800 laths, 12 bushels of lime, 1½ barrels best cow hair, 1¾ yards of sand, ¾ yard of prepared gravel and 16 pounds of cut lath nails, 1¼ inches long. A quarter barrel of lime putty should be mixed with every barrel of prepared gravel for the dash. The dash may be colored as desired by using the proper pigments.
To color 100 yards in any of the tints named herewith use the following quantities of ingredients : For a blue-black, 5 pounds of lampblack; for buff, 5 pounds of green copperas, to which add 1 pound of fresh cow manure, strained, and mixed with the dash. A fine terra cotta is made by using 15 pounds of metallic oxide, mixed with 5 pounds of green copperas and 4 pounds of lampblack. Many tints of these colors may be obtained by varying the quantities given. The colors obtained by these methods are permanent; they do not fade or change with time or atmospheric variations. Earthy colors, like Venetian red and umber, soon fade and have a sickly appearance.
* "Rough-Casting in Canada," by Fred. T. Hodgson, Architecture and Building, March 24,. 1894.
The following description of external plastering, as used by an architect of considerable experience with this sort of work, was published in the Brickbuilder for August, 1895, and probably represents the best current practice in this country :
I have always used three-coat work, the first well-haired mortar and one-third Portland cement, added when ready for use; this coat well scratched. The second coat the same, with the omission of the hair, and the third coat the same proportion, but with coarse sand or gravel, either floated or put on slap-dash, according to the kind of finish I wished to obtain.
I have occasionally used a very small quantity of ochre in this last coat, but it must be mixed very thoroughly and carefully in order to produce an even color.
This plaster work I have used on wood lath over stud without rough boarding behind it. Also on rough boarding with furrings and wood lath, which is better; and over rough boarding with furrings and wire lath, which is the best of all.
A small church plastered in this way on wood lath fourteen years ago is in perfect condition to-day, and various houses built during the last ten years have proved perfectly satisfactory. I have not as yet, however, found any method of building true half-timbered work and making it thoroughly tight without making a wall that was practically as expensive as a brick wall.