defects. Those commonly used, besides sand of various denominations, are powdered sand-stone, brick-dust, and sea-shells and for forming plaster, where closeness rather than hardness is required, lime which has been slaked and kept in a dry place till it has become nearly effete, and powdered chalk, or whiting, and gypsum, in various proportions, besides hair and other materials of a similar nature. Other ingredients have been more lately recommended, such as earthy balls, slightly burnt and pounded, old mortar rubbish, powdered and sifted, and various things of the like kind, the whole of which are, in some respect or other, objectionable.

Plaster of Paris is employed by the plasterer to give the requisite form and finish to all the superior parts of his work. It is made of a fossile stone, called gypsum, which is excavated in several parts of the neighbourhood of Paris, whence it derives its name, and is calcined to a powder, to deprive it of its water of crystallization. The best is Montmartre.

The stones are burnt in kilns, which are generally of very simple construction, being not unfrequently built of the gypsum itself. The pieces to be calcined are loosely put together in a parallelopiped heap, below which are vaulted pipes or flues, for the application of a moderate heat.

The calcination must not be carried to excess; as otherwise the plaster will not form a solid mass when mixed with a certain portion of water. During the process of calcination, the water of crystallization rises as white vapour, which, if the atmosphere be dry, is quickly dissolved in air.

The pounding of the calcined fragments is performed sometimes in mills constructed for the purpose, and sometimes by men, whose health is much impaired by the particles of dust settling upon their lungs.

On the river Wolga, in Russia, where the burning of gypsum constitutes one of the chief occupations of the peasantry, all kinds of gypsum are burnt promiscuously on grates made of wood; afterwards the plaster is reduced to powder, passed through a sieve, and finally formed into small round cakes, which are sold at so much per thousand. These balls are reduced into an impalpable powder by the plasterer, and then mixed with mortar. The less the gypsum is mixed with other substances, the better it is qualified for the purpose of making casts, stucco, &c. The sparry gypsum, or selenite, which is the purer kind, is employed for taking impressions from coins and medals, and

for making those beautiful imitations of marble, granite, and porphyry, known by the name of scagliola, which is derived from the Italian word, scagli.

Finely powdered alabaster, or plaster of Paris, when heated in a crucible, assumes the appearance of a fluid, by rolling in waves, yielding to the touch, steaming, &c. all of which properties it again loses on the departure of the heat if taken from the crucible and thrown upon paper, it will not wet it; but immediately be as motionless as it was before exposed to the heat.

Two or three spoonfuls of burnt alabaster mixed up thin with water, will, at the bottom of a vessel filled with water, coagulate into a hard lump, notwithstanding the water that surrounds it. The coagulating or setting property of burnt alabaster will be very much impaired, or lost, if the powder be kept for any considerable time, and more especially in the open air. When it has been once tempered with water, and, suffered to grow hard, it cannot be rendered of any further use.

Plaster of Paris, diluted with water into the consistence of a soft or thin paste, quickly sets, or grows firm, and at the instant of its setting, has its buik increased. This expansive property, in passing from a soft to a firm state, is one of its valuable properties; rendering it an excellent matter for filling cavities in sundry works, where other earthy mixtures would shrink and leave vacuities, or entirely separate from the adjoining parts. It is also probable that this expansion of the plaster might be made to contribute to the elegance of the impressions it receives from medals, &c. by properly confining it when soft, so that, at its expansion, it would be forced into the minutest traces of the figures.

A plaster of a coarser description, made of a blueish stone, much like that of which Dutch terras are made, is sometimes used in this country, for floors in gentlemen's houses, and for corn-granaries. This stone, when burnt after the manner of lime, assumes a white appearance, but does not ferment on being mixed with water: when cold, it is reduced to a fine powder. About a bushel of this powder is put into a tub, and water is applied till it becomes liquid. In this state it is well stirred with a stick, and used ́immediately; for in less than a quarter of an hour it becomes hard and useless, as it will not allow of being mixed a second time.

Other cements are used by plasterers for inside work. The first is called lime and hair, or coarse stuff, and is pre

pared as common mortar, with the addition of hair from the tan-yards. The mortar is first mixed with a requisite quantity of sand, and the hair is afterwards worked in by the application of a rake.

Next to this is fine stuff, which is merely pure lime, slaked first with a small quantity of water, and afterwards, without any extraneous addition, supersaturated with water, and put into a tub in a half fluid state, where it is allowed to remain till the water is evaporated. In some particular cases, a small portion of hair is incorporated. When this fine stuff is used for inside walls, it is mixed with very fine washed sand, in the proportion of one part sand to three parts of fine stuff, and is then called trowelled or bastard stucco, with which all walls intended to be painted are finished.

The cement called gauge stuff, consists of three-fifths of fine stuff, and one-fifth plaster of Paris, mixed together with water, in small quantities at a time, to render it more ready to set. This composition is mostly used in forming cornices and mouldings run with a wooden mould. When great expedition is required, plasterers gauge all their mortars with plaster of Paris, which sets immediately..

The technical divisions of plasterer's work shall now claim our attention.

Lathing, the first 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, nails made of cast iron may be used. Those mostly used in London are of fir, imported from America and the Baltic, in pieces called staves. Laths are made in three foot and four foot lengths and with respect to their thickness and strength, are either single, lath and half, or double. The single are the thinnest and cheapest; those called lath and half, are supposed to be one third thicker than the single; and the double laths are twice that thickness. In lathing ceilings, the plasterer should use both the lengths alluded to, and in nailing them up, should so dispose them, that the joints be as much broken as possible, that they may have the stronger key or tie, and thereby strengthen the plastering with which they are to be covered. The thinnest laths are used in partitions, and the strongest for ceilings.

Laths are also distinguished into heart and sap laths: the former should always be used in plain tiling; the latter, which are of inferior quality, are most frequently used by the plasterer.

Laths should be as evenly split as possible. Those that are very crooked should not be used, or the crooked part should be cut out; and such as have a short concavity on the one side, and a convexity on the other, not very prominent, should be placed with the concave sides outwards.

The following is the method of rending or splitting laths. The lath-cleavers having cut their timber into the required lengths, cleave each piece with wedges, into eight, twelve, or sixteen pieces, according to the scantling of the timber, called bolts; and then, with dowl-axes, in the direction of the felt-grain, termed felting, into sizes for the breadth of the laths; and, lastly, with the chit, clear them into thicknesses by the quarter grain.

Having nailed the laths in their appropriate order, the plasterer's next business is to cover them with plaster, the most simple and common operation of which, is laying; that is, spreading a single coat of lime and hair over the whole ceiling, or partition; carefully observing to keep it smooth and even in every direction. This is the cheapest kind of plastering.

Pricking up is performed in the same manner as the foregoing; but is only a preliminary to a more perfect kind of work. After the plaster is laid on, it is crossed all over with the end of a lath, to give it a tie or key to the coat which is afterwards to be laid upon it.

Lathing, laying, and set, or what is termed lath and plaster, one coat and set, is, when the work, after being lathed, is covered with one coat of lime and hair, and afterwards, when sufficiently dry, a thin and smooth coat spread over it, consisting of lime only, or, as the workmen call it, putty, or set. This coat is spread with a smoothing-trowel, used by the workman with his right hand, while his left hand moves a large flat brush of hog's bristles, dipped in water, backwards and forwards over it, and thus produces a surface tolerably even for cheap work.

Lathing, floating, and set, or lath and plaster, one coat, floated and set, differs from the foregoing, in having the first coat pricked up to receive the set, which is here called the floating. In doing this, the plasterer is provided with a substantial straight edge, frequently from ten to twelve feet in length, which must be used by two workmen. All the parts to be floated are tried by a plumb-line, to ascertain whether they be perfectly flat and level, and whenever any deficiency appears, the hollow is filled up with a trowel ful! or more of lime and hair only, which is termed filling out,

and when these preliminaries are settled, the screeds are next formed. The term screed signifies a style of lime and hair, about seven or eight inches in width, gauged quite true, by drawing the straight edge over it until it be so. These screeds are made at the distance of about three or four feet from each other, in a vertical direction, all round the partitions and walls of a room. When all are formed, the intervals are filled up with lime and hair, called by the workmen, stuff, till flush with the face of the screeds. The straight edge is then worked horizontally on the screeds, by which all the superfluous stuff, projecting beyond them in the intervals is removed, and a plain surface produced. This operation is termed floating, and may be applied to ceilings as well as to partitions, or upright walls, by first forming the screeds in the direction of the breadth of the apartment, and filling up the intervals as above described. As great care is requisite to render the plaster sound and even, none but skilful workmen should be employed.

The set to floated-work is performed in a mode similar to that already prescribed for laying; but being employed only for best rooms, is done with more care. About onesixth of plaster of Paris is added to it, to make it set more expeditiously, to give it a closer and more compact appearance, and to render it more firm and better calculated to receive the white-wash or colour when dry. For floated stucco-work the pricking up coat cannot be too dry; but, if the floating which is to receive the setting coat be too dry, before the set is laid on, there will be danger of its peeling off, or of assuming the appearance of little cracks, or shells. which would disfigure the work. Particular care and attention therefore must be paid to have the under coats in a proper state of dryness. It may here be observed, that cracks, and other unpleasant appearances in ceilings, are more frequently the effect of weak laths being covered with too much plaster, or too little plaster upon strong laths, rather than of any sagging or other inadequacy in the timbers, or the building. If the laths be properly attended to, and the plaster laid on by a careful and judicious workman, no cracks or other blemishes are likely to appear.

The next operation combines both the foregoing processes, but requires no lathing; it is called rendering and set, or rendering, floated, and set. What is understood by rendering, is the covering of a brick or stone wall with a coat of lime and hair, and by set is denoted a superficial coat of fine stuff or putty upon the rendering. These ope