Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/525

MASON-WOKK.] ngs. Stone pavings are prepared and laid in various ways. Ordinary paving is of self- faced or of tooled York; and for better purposes it is of rubbed Portland stone. For entrance halls, square stones, with the angles slightly cut off, the four spaces thus obtained being filled up by a small square of black or other coloured stone, makes a neat paving, which is replaced by marbles in best houses and public buildings, if a tesselated pavement be not required. Stone paving that is not exposed to the sun and air, if next the ground, should be laid on footings of brick or stone, or it will be constantly damp should the soil be close and clayey; but in yards, open areas, &c., it may be laid on the ground, bedded in sand, and jointed with mortar or cement. Stone-paved floors should be formed on brick arches, or on a timber floor prepared for the purpose ; the latter, how ever, is a very bad mode of supporting paving, as the impression derived from the presence of the stone is, that the floor is incombustible ; but if it be bedded on combus tible material, the danger to Iniman life in the event of fire is greater than if the stone paving did not exist at all. It is worked, cut, and set more or less expensively, according rb.s. to circumstances. A curb is a range or course of thicker and stronger stone to bound a pavement, and is either flush vith the paving showing as a step on its outer edge, or is raised above it to receive a balustrade, and shows on the outer side as a blocking course ; in the latter situation it is generally joggled and plugged in the joints. The term ps. step or steps alone is usually understood to mean external steps, whether arranged in long or short flights, or the single step in a doorway into which the door-frame is tenoned. A step should have a plain horizontal bed, and a very slightly weathered tread or upper surface, the front or riser worked plain and vertical, or with a moulded nosing, and the back sunk with a joggle or bird s-mouth joint to receive the step or landing above or behind it. Steps for areas or back courts are often made of 2 or 2| in. stone for the tread, the riser being formed of a 4 or 3 in. stone, both tailed into a wall at one or both ends. This is much lighter in effect. Slate is sometimes used for the treads. ii s. Stairs are but a flight or combination of steps used in ternally, and the general principle of designing staircases, as regards the rise and tread of steps, setting out curves, curtails, landings, &c., are given in the part treating of joinery. The chief difference between these and other staircases consists in the fixing, the one being framed with wooden strings, while the other have no strings, but are supported entirely by the walls. If there be a wall at each end, they are simply built in at the time the work goes up ; but if they are supported at one end only, they are called geometrical stairs, and depend entirely on their being securely wedged into the wall ; on which and on the sup port each derives at one edge from the step below, they wholly rely. If they are square in section, they are called solid steps ; but as the under side or soffit, then, is irregular, it is usual to make the steps of somewhat a triangular shape, so as to present a continued soffit. In this case they are called arris, or feather-edge steps. Care should be taken that there are no sudden or irregular changes in the curves. These may be easily avoided by the method shown in the portion relating to joinery for the easing of the curves and ramps in handrails. In houses built of stone the flues are usually formed in > imney- brickwork. The chimney-pieces consist of plain jambs, or boxings, or other vertical sides more or less decorated and moulded, and of the architrave or transverse covering or mantel, fig. 8, Plate XXI., with its shelf or cornice. The parts of a chimney-piece are generally put together with an adhesive plaster or cement, and affixed to the vall or chimney-breast behind with cramps, holdfasts, 473 and plugs. The material of which chimney-pieces, if not of wood, are composed, varies from the coarsest stone to the finest marble ; and the labour on them varies to a still greater extent. Masonry to receive architectural decorations is generally Decorate worked into the walls as they are carried up ; but as they ma sonry. are seldom homogeneous either in matter or construction, the result is mostly the converse of what it purports to be, for the work is more frequently weakened than strengthened by the decorative masonry. Stones of which columns are Columns, to be composed, whether each column is to be of one stone or more, are generally roughly boasted out before they are set, and are finished afterwards to traversing moulds and templets with a plumb-rule, whose sides are cut to the diminution obtained from the bottom and upper diameters, whatever it may be. Flutes are cut at the same time and in the same manner. The beds of the joints in columns should be worked with the greatest precision, so as to obtain parallel planes, that they may fit firmly and closely together; they must not, however, be worked hollow to make a close joint externally, or the arrises will chip off. It is considered a good plan, where the columns are large, to put a piece of thin milled lead between the beds, cut circular, and extending to within a short distance of the surface, and that the rest be filled with a fine adhesive putty, made as nearly of the colour of the stone as possible. This makes a solid bed, and protects the arrises effectually ; but it will not do so well for slight columns, because it narrows the bed so materially. A joggle or dowel of hard wood, slate, or cast-iron let into the core might be a sufficient counteraction, and it would certainly add to the stability of a polylithic shaft. The other parts of a columnar composition may be sufficiently cramped and joggled together with wood and metals, according to the situation, though it may be again re marked, that neither wood nor metal should be used, unless it can be protected from access even of the atmo sphere. Sections for Roman mouldings are given in the part Greek and relating to joinery, but as those used in Grecian architecture Koman are parts of conic sections, and not struck by compasses, m we give a short problem by which they may all easily be set out. Both Roman and Grecian mouldings are shown on Plate XIII. -of vol. ii. Let an ovolo be the moulding required (fig. 21), the height of which (to the point where the moulding curves backward) is AC or BD, and the greatest projection AB or CD ; and let CE be a tangent line, or line which the curve must touch but not cut. Produce CA to F, and make AF equal to AC, and AG to ED. Divide GB BE each into the same number of equal parts as 5. Draw the co-ordinates from F and C to the respective numbers, their intersections will trace the curve. If BE be more than half the whole height, the curve is an ellipse ; if exactly half the height, itis a parabola; and if BE be less than half BD, the curve will be a hyperbola. All other mouldings can be drawn by this method, it being re membered that cymas, ogees, and all reflex curves, must be divid ed and drawn in two separate portions. The mouldings in mediaeval architecture differ entirely Mediaeval from those of other styles. They are chiefly formed by a mouldings combination of curves stopped by right lines or worked into other curves and hollows. The mouldings differ in IV. 60 21. -Construction of

Ovolo.