The Plasterer is a workman to whom the decorative part of architecture owes a considerable portion of its effect, and whose art is requisite in every kind of building.

The tools of the plasterer consist of a spade or shovel of the usual description; a rake, with two or three prongs, bent downwards from the line of the handle, for mixing the hair and mortar together; trowels of various kinds and sizes; stopping and picking-out tools; rules called straightedges; and wood models.

The trowels used by plasterers are more neatly made than tools of the same name used by other artificers. The laying and smoothing tool consists of a flat piece of hardened iron, about ten inches in length, and two inches and a bali wide, very thin, and ground to a semicircular shape at one end, but left square at the other; and at the back of the plate, near the square end, is rivetted a small iron rod with two legs, one of which is fixed to the plate, and the other to a round wooden handle. With this tool all the first coats of plaster is laid on, as are also the last, or, as it is technically termed, the setting. The other kinds of trowels are made of three or four sizes, for gauging the fine stuff and plaster, used in forming cornices, mouldings, &c. The longest size of these is about seven inches on the plate, which is of polished steel, about two inches and three quarters broad at the heel, diverging gradually to a point. To the heel or broad end a handle is adapted.

The stopping and picking-out tools are made of polished steel, of different sizes, though most generally about seven or eight inches in length, and half an inch in breadth, flattened at both ends, and ground somewhat round. These tools are used in modelling and finishing mitres and returns to cornices; as likewise in filling-up and perfecting the ornaments at the joinings.

The straight-edges are for keeping the work in an even, or perpendicular line; and the models or moulds are for run

ning plain mouldings, cornices, &c.; of these latter the plasterer requires a great number as very little of his finishing can be done without them.

Experienced workmen keep their tools very clean, and have them daily polished by the hawk-boys.

Plasterers have technical divisions of their work, by which: its quality is designated, and value ascertained; as, lathing; laying; pricking-up; lathing, laying, and set; lathing, floating, and set; screed, set or putty; rendering and set, or rendering, floated, and set; trowelled stucco, &c.; each of which, hereafter, we shall very minutely explain.

In all the operations of plastering, lime extensively abounds; we shall, therefore, first offer some observations on the properties of this important article.

All who have written on the subject of lime, as a cement, have endeavoured to ascertain what is the due proportion of sand for making the most perfect cement; but with a little attention it is evident, that all prescribed rules must be so very vague and uncertain, as to be of little utility to the workman, for, besides the variation which is occasioned by a more or less degree of calcination, it is a certain fact, that some kinds of lime-stone are much more pure, and contain a much smaller proportion of sand than others; consequently, it would be absurd to say, that pure lime requires as small a proportion of sand, when made into mortar, as that which originally contained in itself a large proportion.

The variation thus produced, in regard to the proportion of sand, is found to be extremely great. It is, however, stated, that the best mortar which has come under examination, was formed of eleven parts of sand to one of lime: to which was added, by measure, between twice and thrice its own bulk of sand, which may be allowed to have been at least three times its quantity by weight. Supposing, therefore, that every particle of the lime had been so perfectly calcined as to be in a caustic state, there could not be less than forty-seven parts of sand to one of lime; but it is hard to suppose, that above one hundredth part of this mass, independent of the water, consisted of pure caustic calcareous earth.

From these considerations it is conceived, that it is impossible to prescribe any determinate proportion of sand to lime, as that must vary according to the nature of the lime, and other incidental circumstances, which would form an infinity of exceptions to any general rule. But it would

seem, that it might be safely inferred, that the moderns in general rather err in giving too little, than in giving too much sand. It deserves, however, to be noticed, that the sand, when naturally in the lime-stone, is more intimately blended with the lime, than can possibly be ever effected by any mechanical operation; so that it would be in vain to hope to make equally good mortar artificially from pure lime, with so small a proportion of caustic calcareous mat ter, as may sometimes be effected when the lime naturally contains a very large proportion of sand. Still, however, there seems to be no doubt, that if a much larger propor tion of sand than is common were employed, and that more carefully and expeditiously blended and worked, the mortar would be made much more perfect, as has been proved by actual experiments.

Another circumstance, which greatly tends to vary the quality of cement, and to make a greater or smaller proportion of sand necessary, is, the mode of preparing the lime before it is beaten up into mortar. When for plaster, it is of great importance to have every particle of the limestone slaked before worked-up, for, as smoothness of surface is the most material point, if any particles of lime be beaten-up before sufficiently slaked, the water still continuing to act on them, will cause them to expand, which will produce those excrescences on the surface of the plaster, termed blisters. Consequently, in order to obtain a perfect kind of plaster, it is absolutely necessary that the lime, before being worked, be allowed to remain a considerable time macerating or souring in water: the same sort of process, though not absolutely required, would considerably improve the lime intended for mortar. Great care is required in the management; the principal thing being the procuring of well-burnt lime, and allowing no more lime, before worked, than is just sufficient to macerate or sour it with the water: the best burnt lime will require the maceration of some days.

It has been almost universally admitted, that the hardest lime-stone affords the lime which will consolidate into the firmest cement; hence, it is generally concluded, that lime made of chalk produces a much weaker cement than that made of marble, or lime-stone. It would seem, however, that, if ever this be the case, it is only incidentally, and not necessarily. In the making of mortar, other substances are occasionally mixed with lime, which we shall here proceed to notice, and endeavour to point out their excellencies and

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 bu.k 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 & second time.

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