PLASTERING, the art of covering the walls and ceilings of a house, or other edifice, with a composition, of which the work is lime and hair-mortar, finished with a coating of finer materials. It is of various kinds ; as white lime and hair mortar on bare walls ; the same on laths, as in par titioning and plain ceiling; renewing the insides of walls, or donble-partition walls; rough-casting on heart-laths; plas tering on brick-work, w ith finishing-mortar, in imitation of stone-work, and the like upon heart-laths; modelling and casting ornamental and plain mouldings ; and making and polishing- the scagliola for columns of wood or brick and their antte.
In all the operations of plastering, lime forms an extensive article, as it pervades the whole; and for its nature, proper ties, and preparation, the reader is referred to the word Lime; suffice it here to remark, that most of the lime used in London is prepared from chalk-, and is brought thither ti-ow Purfleet, in Kent ; but for stuccoing, and other work requiring strength and permanency, that which is made at Dorking, in Surrey, has a decided pre-eminence.
Next to lime, the plasterer depends much on what is called plaster of Paris (see that article) ; for this alone enables him to give the required form and finish to ali the superior parts of his business. With this he makes his ornaments and cornices ; and lie also mixes it with the lime for filling up the concluding coat to the walls and ceilings of rooms. The name of this composition is derived from the circum stance of its abounding in the hills of Montmartre, in the environs of the French capital ; but what is chiefly used in London is prepared from a sulphate of lime dug in Der byshire.
Cements used by plasterers for inside work are of two or three kinds; the first is called lime and hair, or coarse stuff, and is prepared as common mortar, only with the addition of hair from the tan-yards being mixed with it. The mortar is first mixed with the requisite quantity of sand, and then the hair is worked in by the labourer with the rake.
Next to this is fine stall', consisting of pure lime slaked with a small quantity of water, and then, without any extra neous addition, supersaturated with water, and put into a tub in a half-fluid state, where it remains till the water is evapo rated. In particular cases, a small portion of hair is some
times worked into this fine stuff, before it is laid on.
For inside walls, this fine stuff is mixed with very fine washed sand, in the proportion of one part sand to three parts of fine stuff, and then it obtains the name of troweled, or bastard stucco, with which all walls intended to be painted are finished. consists of three-fifths of fine-stuff and one-filth of plaster of Paris, mixed together with water, in small quantities at a time, to render it more ready to set, or fix itself. This cement is mostly used in forming cornices and mouldings run with a wooden model. When great ex pedition is requisite, plasterers gauge all their mortars with plaster of Paris, which enables them to proceed with their work, because it sets as soon as laid on.
Next to the materials, the technical divisions of the plas terers' work claim attention, and are as follow :- 1. Lathing: this operation consists in nailing laths on the ceiling or partition. If the laths be of oak, they will require wrought-iron nails; but if of deal, east-iron nails may be used. Those mostly used in London are of fir, imported from the Baltic and America, in pieces called staves. Laths are made in three-foot and four-foot lengths; and, with re spect to their thickness and strength, are either single, lath and-half, or double. The single are the thinnest and cheapest ; those called are supposed to be one-third thicker than the single; and the double laths are twice their thickness. In lathing ceilings, the plasterer should use both the lengths alluded to ; and, in nailing them up, he should so dispose them that the joints may be as much broken as pos sible, that they may have the stronger key, or tie, and thereby strengthen the plastering with which they are to be covered. The thinnest laths arc used in partitions, and the strongest for ceilings. See LATH.