PLASTER-WORK ON EXTERIOR OF WALLS.
In plastering on stone and brick, only one coat of brown mortar is used. In this hair is not considered essential, but a little more sand than usual is added to the mortar. The wall should be well dampened before the ap plication is made, and the mortar itself is made more plastic, works more easily, and attaches more quickly to the wall when thinned with water. When too little sand is used, the plaster is apt to crack in setting and drying, and crumbles easily; almost the same effect results from too much sand; so that a knowledge of the sufficient quantity can be obtained only by experi ence. Upon external walls the second coat should consist wholly or par tially of cement, equal parts of lime and cement making an excellent com position. If the wall be exposed to the effects of water and frost, the in troduction of sifted sawdust mixed with the water will prevent the scaling off of the plaster. When the work is done in dry and windy weather, the wall should be frequently sprinkled with water, to prevent too great rapid ity in drying, and in damp places cement should be used instead of fat lime. The work in cement must be executed rapidly, and only so much mortar mixed as can be used before it begins to set.
—This cheap and excellent covering for outer walls, when they are protected by projecting- eaves, is applied in the following- manner: The surface is indented or roug-hed and then well brushed, to cleanse it from loose fragments. It is then covered with the rough-cast, which is mortar thinned by water to which pure lime is added to make it of the con sistence of cream. By another process the roughened wall is sprinkled with water and coated with lime and hair; when this is set, a second coat is laid smoothly, and upon this is dashed an almost fluid mixture of fine gravel and strong- lime well mixed. This last is immediately washed with an ochreous color, and dries into a compact mass. When plaster is directly applied to brick, concrete, stone, or other surfaces than lathing-, the work of putting on the first coat of coarse'inaterial is termed " rendering- " in stead of laying or plastering; and therefore, although the material applied and method of application are the same as on lathing, one-coat work is termed " render;" two-coat work, " render-set."
Stucco.—The common quality of stucco is composed of one part of lime to three or four parts of clean-washed sand. When employed with coarse sand for finishings in imitation of stone, it is called "rough stucco," the surface, to give it an appearance of the grain of sandstone, being raised by rubbing with a hand float or small flat board with a handle at the back. In the composition of stucco, there are four bushels of fat lime to one bushel of hydraulic cement, with sand as six parts to one. A setting or finishing coat in cominon plastering is called " fine-stuff," and consists of a pure liine slaked with a small quantity of water, being afterward thinned to the consistence of cream. It is left to settle; the surface water is drained off, and then the mass is allowed to evaporate until thick enough for use, when it is usually styled " putty." kinds of cements are used to obtain a hard, non-porous surface capable of resisting weather. Portland cement is almost universally employed for external walls, haying superseded Roman cement, which, although valuable as quick-setting-, is not considered reliable. A superior quality of the Roman—known as the Medina—cement is of a lig-liter brown color, sets rapidly, and has borne exposure to water. Mastic, well suited to outside work which is to be painted immediately, is expensive, and metallic cements, having a metallic lustre intended to dispense with color ing or painting-, have been used to some extent.
Sgraffilo is a revival of an old Italian method of decoration. The pro cess may be briefly described as follows: A coat of colored plaster of the tint of the proposed design is applied to the wall, and upon this is placed another coat of the tint intended for the grounding color. A mould in zinc of the outline of the intended design is then fixed on the surface; its outer edge is traced, and the upper coat of color is then cut away with a sharp tool down to the face of the lower coat. Eyen three coats are some times applied, and a considerable variety of coloring is thus produced. A good specimen of this work is displayed on the outer walls of the National Training School of Music, South Kensingrton, London.