Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/568

Rh 506 BUILDING [rLASTER-WORK. with the end of a lath in parallel lines from 3 to 4 inches apart. The scorings should be made as deep as possible without laying bare the laths ; and the rougher their edges are the better, as the object is to produce a surface to which the next coat will readily attach itself. When the pricked up coat is so dry as not to yield to pressure in the slightest degree, preparations may be made for the floating. Ledges or margins of lime and hair, about 6 or 8 inches in width, and extending across the whole breadth of a ceiling or height of a wall or partition, must be made in the angles or at the borders, and at distances of about 4 feet apart throughout the whole extent; these must be made perfectly straight with one another, and be proved in every way by the application of straight edges ; techni cally these ledges are termed screeds. The screeds are gauges for the rest of the work ; for when they are ready, and the mortar in them is a little set, the interspaces are filled up flush with them; and a derby float or long straight edge being made to traverse the screeds, all the stuff that projects beyond the line is struck off, and thus the whole is brought to a straight and perfectly even surface. To perfect the work, the screeds on ceilings should be levelled, and on walls and partitions plumbed. When the floating is suffi ciently set and nearly dry, it is brushed with a birch broom as before described, and the third coat or set is put on. This for a fine ceiling that is to be whitened or coloured must be of putty ; but if it is to be papered, which is very unusual, ordinary fine stuff, with a little hair in it, will be better. Walls and partitions that are to be papered are also of this latter, or of rough stucco, but for paint the set must be bastard stucco trowelled. This coat must be worked of exactly the same thickness throughout, to pre serve to the external surface the advantage that has been obtained by floating. For all but the last-mentioned, the set on floated work, the trowel and brush are considered sufficient to produce fine and even work ; but trowelled stucco must moreover be hand floated. In this operation the stucco is set with the trowel in the usual manner, and brought to an even surface with that tool to the extent of two or three yards. The workman then takes the hand- float in his right hand, and rubs it smartly over the surface, pressing gently to condense the material as much as pos sible. As he works the float he sprinkles the surface with water from the brush in his left hand, and eventually produces a texture as fine and smooth almost as that of polished marble. But lathing and plastering on laths as practised in England is at best a very flimsy affair, and greatly requires improvement. Stronger laths than the laths commonly employed, put on further apart, and with headed wrought nails, and the plastering laid on upon both sides in upright work, or both above and below the ceilings at the same time, two men working against one another, will produce work in some degree worthy of the name. The practice of the French in this respect is well worthy the consideration, and to a great extent the imitation, of English plasterers. Plasterin.&amp;lt;; The process of plastering on the naked brick or stone wall differs but little, except in name, from that we have described as the mode on lath. The single coat is called rendering, and it need differ only in the quantity of hair, which may be less than is necessary for laying on lath, and in the consistence of the mortar, which may be made more plastic, to work easier, and because in a moister state it will attach itself more firmly to the wall ; the wall, how ever, must itself be well wetted before the rendering is applied. The set is the same, and is put on in the same manner as to two-coat work on lath. For three-coat or floated work, the first or rough rendering should be made to fill up completely whatever crevices there may be in the on walls. work behind it, and be incorporated with it as much as possible. As its name imports, its surface may, indeed should, be rough ; but it is not scratched or lined as the similar coat on lath is. For this, too, the wall must be pre viously wetted, that the mortar may the better attach itself to it. For the floating, screeds must be formed as before described, and the consecutive process is exactly the same as on lath, both for the floated and for the set coat. In almost every case in which plastering is to be floated, the workman finds a guide for the feet of his wall screeds in the narrow grounds which the joiner has previously fixed for his skirtings; from these he plumbs upwards, and makes his work perfectly flush, with them. Mouldings and cornices (as large combinations of mould- Mouldi: ings and flat surfaces immediately under the ceilings of ancl . rooms are called) are formed with running moulds, and are co generally executed before the setting coat is put on the walls and ceiling. If the cornice do not project more than about an inch and a half, or 2 inches, from the ordinary work, a backing of lime and hair will be sufficient ; and if any one part only happen to be more than ordinarily pro tuberant, a row of nails from G to 12 inches apart stuck into the wall or ceiling in the line of that part will give it sufficient support. But if the general mass of the cornice be more than that amounts to, and extend more than G or 8 inches along the ceiling, it must be bracketed out, and the bracketing lathed and pricked up, as for ordinary work. This pricking up, or other preparation, must of course be perfectly set before the cornice is run ; and there should be one-fourth of an inch, at least of clear space between the preparation and the mould in the nearest part. A wooden screed or parallel straight edge is tacked on with brads to the wall, and another on the ceiling, if the cornice be large and heavy, as guides or gauges for the mould, whose rests are chased to fit them ; ancl then one man laying on gauge stuff in an almost fluid state with un angular trowel, another works the mould backwards and forwards over it, which strikes off what is superfluous, and gives the con verse of its form to the rest. The mould is never taken down from the work at right angles to the line of it, but is drawn off at the end, so that none of the parts of the moulding or cornice is injured or torn by it, which must otherwise frequently be the case, from the peculiar forms at times given to the details. If a cornice be too large and heavy to be executed at once, it may be done in the same manner at two or more times, in so many parts ; and if any part or parts of a moulding or cornice is to be enriched, the space for it is left vacant by the mould, and the enrich ment is afterwards supplied. As a cornice cannot be completed up to the angles by the mould, it is worked by hand in those situations to a joint. The joinings are termed mitres, and in forming them the plasterer uses the jointing tools we have already described. Models for enrichments are made by the modeller, Enrich according to the design or drawing submitted to him, and ment s. from them the plasterer makes wax or gelatine moulds, or, as in ordinary practice, the modeller supplies the moulds in which the ornament is cast in plaster of Paris. If the ornament be in recurring lengths or parts, as is usually the case, only one length or part is modelled, and casts of as many as are required are taken from the mould ; some single ornaments, again, which are very large, require to be moulded and cast in parts, which are put together by means of cement. When the cast ornaments are sufficiently dry the pieces are scraped and trimmed, and the joints made clean and even ; and they are set in the cornice with plaster of Paris, with white lead, or with a composition called iron cement, as the case may require. If the castings have something in the cornice to rest upon, the first will do ; but if there is nothing to retain or attach them but the