Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/569

Rh PLASTER- WO UK.] BUILDING 507 cement, one of the last two must be used. Flowers and other ornaments on ceilings which aro too large and heavy to be trusted to adhesive matter alone, must be screwed to wooden cradling behind and above them. In plastering a wall with common stucco (and its use is mostly for outside work), the first thing to be done is to remove tho dust from it by brushing, and then to wet very completely with water If the wall to be stuccoed be an old one, or one of which the joints have been drawn, the mortar of the joints must be chipped or even raked out, and the bricks picked, to expose a new and porous surface to tlio plastering before brushing and wetting. The wall is then covered with stucco in a fluid state, applied with a broad and strong hog s bristle brush, like common white washing, When this is nearly dry the stucco must be laid on as in common rendering, unless the work is to be floated, when the process is nearly similar to that in floated plas tering. Screeds mast be formed at che highest and lowest extremities of the wall, or of that part of the wall which is in the same vertical line, and is not intercepted by string courses, and be returned at the angles, putting the whole surface into a sort of frame. These must be made perfectly straight and plumb, so as to be quite out of winding by the careful application of the plumb-rule and straight edge. Inner vertical screeds must then follow at three or four feet apart across the whole surface, and be made to range exactly with the outer ones, and then the interstices must be filled in as before. As the work is made good it must be well rubbed with the hand float, as in the execution of trowelled stucco internally, to compress the material, and produce a hard, even, and glossy surface. Preparations for cornices and other projections from the straight surface of the work must have been previously made in or on the brick or stone-work by the protrusion of bricks, tiles, or whatever may be best suited to form a core ; and the mouldings and cornices are run with moulds, in the manner described for the same things internally, only that in work of this kind no plastic material but the stucco itself is used, that is, there is no preparation of any softer material than the stucco itself put under it. In running cornices in this material, workmen are very apt to mix a little plaster of Paris with tho stucco to make it set under the mould, and thus give sharpness and fulness to the mouldings; but this should not be permitted ; for the plaster is not qualified to stand the weather as the stucco is, and, if mixed with it, will produce premature decay. When the stucco is perfectly dry, it may be painted in oil colours, or bo coloured in distemper ; and in either case it is generally (though not invariably) ruled over the surface with a lead point, to give it the appearance of gauged stone-work. Rendering in the Roman and Portland cements is executed almost exactly in the same manner as stucco rendering is, only that it is laid on the saturated wall directly, without the preliminary operation of roughing in, o&quot; washing the surface with a solution of the material. The same process, too, is followed in floating this cement, and with the same exceptions ; and as, in addition to its superior hardness and capacity for duration, it is a quick- setting cement, it is far preferable to any of the common stuccoes for running cornices, mouldings, &v. These cements may, like stucco, be painted in oil, or coloured; but instead of a size colour, which is used for almost every other purpose in plastering, the colour for this com position is mixed with diluted sulphuric acid. This too may be lined and tinted to imitate stone and stone-work of any description. It may not be amiss here to refer to some of the causes of the premature decay which takes place in stuccoes and cements when used externally as a coating to walls. The primary cause is the presence of muddy earth and decayed animal and vegetable matter in the sand used with the lime and cement. To this may be added frequent im purities in the limes and cements themselves, particularly of argillaceous matter in the former, and sometimes the too great proportions of lime or cement to sand. These things might, however, remain quiescent for a long time, if the work were well protected from access of moisture, which is the grand exciting cause. The paint, or distemper wash, on the surface, is generally sufficient to prevent the rain which may beat against a vertical face from penetrat ing, especially if the work have been well hand-floated and trowelled, to make it close and compact ; but the evil arises from exposure above, and from the numberless horizontal unfloatcd surfaces which are constantly pre sented. These receive and collect the water, and convey in streams over the vertical surfaces what is not imme diately absorbed ; and the work thus becoming saturated, frost seizes and bursts it, or warmth calls the vegetative powers of the impurities in it into action, and the whole is covered with a green sward. Let the sand of which a plaster composition is to be formed, whether with lime or cement, be washed until it no longer discolours clean water, and be well compounded with cementitious matter free from impurities with which it is so frequently charged ; let the work be well hand-floated and trowelled, particularly on the backs or upper horizontal surfaces of projections, and protected above by projecting eaves or otherwise ; and the work, with common care and attention to paint or distemper at intervals, will last as long as anything of the kind can be expected, or is found, to last anywhere. A cheap and useful covering for external walls, which are Rough cast protected by projecting eaves, in plain buildings, is rough cast. This is executed in the following manner : The surface is first roughed, or indented, and then well brushed with a stiff brush to remove all dust or loose earth. It is then covered with the rough cast, which consists of a small quantity of mortar diluted with water, to which a trowel of pure lime is added to make it about the thickness of cream. After the workman has done all within his reach the scaffolding is lowered, and he proceeds with the remainder. Another process is somewhat dearer. After having been roughed or indented, the wall is sprinkled with water, and then rendered with lime and hair ; and when that is set, another coat of the same material is superadded, laid as evenly as it can be without floating, and as soon as a piece of two or three yards in extent is executed, the workman lays on it an almost fluid mixture of clean fine gravel and strong lime, which have been well mixed together. This is immediately washed with any ochreous colour that may be desired, and the whole dries into one compact mass. A third process, called stuccoing, is performed by the workman laying on a few trowels of stucco, which he spreads as much as possible ; a second workman provided with a brush and a small wood float follows him, and after sprinkling the mortar with water lie rubs over that part he has wetted with the float, and at the same time it may be whitened with lime alone. When the lime is very good this makes very good work. In renovating and repairing plastering the whole surface Repairs, is first well washed to remove the dirt which may have attached itself, and as much of the earthy matter of the previous coat of whitening or colouring as will come away ; any injuries the work may have received, such as cracks and fractures, are then repaired ; and when the new stuff is quite dry, the joinings are scraped to produce an even surface, and the whole is again whitened or coloured once or twice or oftener as may be required, to make it bear out well. Stuccoed walls which have been painted must