Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/566

04 BUILDING [PLASTER-WORK. PLASTER-WORK. No art in the economy of building contributes more to produce internal neatness and elegance, and no one is less absolutely important, so far as the use and stability of a structure are concerned, than that of the plasterer. The very general application of plaster is of compara tively late date ; for wainscoted walls, and boarded or boarded and canvased ceilings, or naked joists alone, are frequently found in houses of rather over a century old, both in England and on the Continent ; and a return to this state of completion in the present day is the result of the attempts of the mediaeval school of archi tects, and their cry of " no shams," which has not been quite successful among themselves, for plaster and cement are used by many. The walls of houses were formerly plastered above the wainscoting and coloured, while the ornamented plaster ceilings of the time of Henry VIII., Elizabeth, and James I., are still the admiration of lovers of the art. Still earlier specimens of the plasterer s skill are extant in the pargetted and ornamented fronts of half- timber houses. Tools For the more common operations of plastering compara tively few tools and few materials are required. The plasterer is attended by a labourer, who supplies his boards with mortar, and by a boy on the scaffold with him to feed his hawk, which is a piece of wood about 10 inches square with a handle under it, for carrying up small por tions of plastering mortar to the wall or ceiling, to be there delivered and spread by the trowel, a thin plate of hardened iron or steel with a wooden handle, similar to that used by the bricklayer. The plasterer is obliged to keep this implement particularly clean and dry when he is not actu ally using it, lest it rust in the slightest degree, as it is clear that the brown oxide of iron would sadly discolour his finer work on touching it again with the trowel. He is necessarily furnished with a lathing hammer, a hand float, a quirk float, and a derby or darby, which is a long two-handled float for forming the floated coat of lime and hair ; brushes for fine or rough work ; three or four jointing trowels for mitres, &c. ; jointing rules ; moulds for cornices, which are of wood, but for work of any importance the frame is made of wood and the outline cut out of a copper (or more usually zinc) plate, these are inserted in the wooden stock, and narrow pieces of wood are fixed to the moulds transversely to guide and steady them along the screeds ; a straight edge, wherewith to bring the plastering on a wall or ceiling to a perfectly even surface by traversing it in every direction ; a screen, having metal wires to act as a sieve for separating the coarser materials which enter into the composition of plastering mortar, these are thrown against its outer face, to separate the particles which are too large for the purpose from the finer, the sand and lime, too, are mixed much more efficiently and completely by screening them together than in any other manner ; a spade and hod like those of the bricklayer s labourer ; a rake to separate the hair used in the mortar and distribute it throughout the mass ; and a server for the hawk boy to beat up the mortar, and to deliver it in small pats on the hawk. Materials. The plasterer, as the term imports, works in plastic, adhe sive compositions, which are laid on walls, both internally and externally, to stop crevices, reduce inequalities, and produce an even, delicate surface, capable of receiving any decoration that may be applied to it, either in colour or otherwise. These compositions are as various as the modes of applying them, the rudest being a compost of loam, a marly clay, and lime ; this is used only for the commonest purposes, and being laid on in one coat, is washed over with a thin mixture of lime and water, a process termed lime-whiting. There are many grades from this to the highest work of the plasterer, the making imitations of marbles and other costly stones, from the purest calcined gypsum mixed with a solution of gum and isinglass and colouring matter to produce the required imitation. His materials are laths, lath nails, lime, sand, hair, and plaster, a variety of stuccoes and cements, together with various ingre dients to form colouring washes, &c. Scaffolding is not Scaff&h generally required for new work, but with old work it is sometimes necessary. Under ordinary circumstances, the plasterer is enabled to wash, stop, and whiten the ceil ings and walls of rooms from trestles, with boards laid across them. In lofty saloons and halls, churches, &c., scaffolding is indispensable. It is necessary, too, to a front that is to be plastered in any way ; but this may be afterwards washed, repaired, and coloured from a ladder, without the interven tion of a scaffold, except perhaps the suspended scaffold now so much used. Laths are narrow strips of some straight-grained wood, Lathii: generally of fir, though oak laths are sometimes used, in lengths of 3 and 4 feet, or to suit the distances at which the joists of a floor or the quarterings of a partition are set, and in thickness from ~th to ths of an inch ; those of the greater thickness are called lath and a half. Lath nails are either wrought or cut ; cut nails are in common use in England with fir laths. Coarse stuff is composed of ox Coarse or horse hair from the hide, in addition to lime and sand stuff, mortar ; this is intended to act as a sort of mesh to net or tie it together, and form a coarse but plastic felt. The hair should be long, and free from all grease and filth. Road drift is unfit to be used in place of clean sharp sand in mortar, unless it be completely cleansed from all animal and vegetable matter, and of mud and clay. Fine stuff is made of fine white lime, exceedingly well Fine st slaked with water, or rather macerated in water to make the slaking complete ; for some purposes a small quantity of hair is mixed up with this material. The mere paste, when allowed to evaporate until it is of a sufficient consistence for working, is called putty. Gauge stuff is composed of Gauge about three-fourths of putty and one-fourth of calcined stuff. gypsum or plaster of Paris ; this may be mixed only in small quantities at a time, as the plaster or gauge renders it liable to set very rapidly. Bastard stucco is made of stucco two-thirds fine stuff, without hair, and one-third of very fine and perfectly clean sand. Common stucco is composed of about three-fourths of clean sharp sand and one-fourth of the best lime, well incorporated. This must be protected from the air from the time it is made up until it is required to be laid on the walls. Parker s (or Parker s Roman) cement, when of good quality, with fine clean sharp sand, Cemer in the proportion of about three of sand to one of cement, and well executed, forms a very good external coating for walls. It is vulgarly called " comps," a contraction of " com position." Portland cement, so called because the mortar formed by it when mixed with sand is supposed to present the appearance of stone from the Portland quarries, is in much esteem for an outside stucco, as the colour to which it dries is sufficiently agreeable to the eye without any colouring wash, whereas Parker s cement is too often of a dark dirty tint, requiring painting or colouring to render it tolerable. Portland cement is also much valued as being proof against water when used as a mortar in setting brick work, and in the composition of concrete for foundations. The patent selenitic cement already described (page 459), is stated to be an excellent substitute for Portland cement ; it takes double the usual quantity of sand, and is stronger even then than ordinary mortar. Plastering is finished in much less time than by the common mode. A class of cements capable of taking a brilliant polish resembling marble, and consequently very suitable for

internal decoration, deserves to be mentioned. The chief