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SECT. IIIA.

USE OF MARBLE.

2002aa. The Greek term "marble," to flash, gleam, sparkle, is well applied to the white marbles of the Greeks, which differed materially from those of Carrara, in Italy. The Greek and Roman marbles are noticed in the GLOSSARY. The Byzantine interiors exhibit fine examples of durable applied marble decoration, about one inch thick, showing no desire to appear anything different. The walls were covered with oblong panels in tiers of rich marbles opened out, framed with narrow white mouldings and bands of different colour, continuous horizontal lines of colour on white being introduced between these panels; the whole surmounted by a marble mosaic frieze, with a cornice displaying small, sharp, triangular shadows, as at Constantinople and St. Mark's at Venice. At Palermo the panels were framed with bands of mosaic work.

200266. The marble pavements of Greek temples were probably the earliest and were usually of thick, large slabs. They perfected the tesselated mosaic pavements. The Romans gained the knowledge from them, became proficient, and used them throughout their extensive empire. Although under half an inch square, the mosaic is one inch thick, made to last. Some of the grandest pavements are the simplest, as those of the Basilica Julia at Rome, of Santa Sophia, and the one under the central dome of St. Mark's. That of the Basilica Julia has been lately discovered, and is very p rfect in part. The plan is a rectangle of about two squares, the centre space being divided into three squares and four broad bands. The squares consist of large slabs of Giallo antico, with a broad border of Pavonazzetto, the bands being rectangular slabs of rich Africano and Porta Santa. The central slab is surrounded for about fifty feet with large slabs of Greek white marble.

2002cc. The Opus Alexandrinum pavements, as at St. Mark's and at Westminster Abbey, were usually composed of few colours-red and green porphyries with white Palambino for the mosaics, the bands being Greek white marble, and made out of old materials: a great variety of geometrical patterns. Some of the most beautiful examples are at Palermo. The Palambino was a limestone of pot-like texture. The great pavement in Siena Cathedral, one of the finest Italian Renaissance works, consists of pictorial subjects in dark green marble and mastic inserted into thick slabs of white marble. These have not worn well, and are kept covered. The filled-in lace-like patterns used as borders round the monuments at Sta Croce, at Florence, are in a better condition, the fillings being in smaller quantities. These fillings might be of lead set in a white ground, and would look well. Black and white marble pavements in squares were introduced about the time of Torregiano, and were largely used, as at King's College Chapel, Cambridge; the Beauchamp Chapel at Warwick; and in mansions generally. The white squares came from Italy, and the black from Belgium; and are still used in that country.

2002dd. The retiring grey marbles, as Petworth, Purbeck, or Frosterley, were used by the medieval builders in England, and the colour was most useful in contrast with the stone. The altars and tombs of the Italian Renaissance were executed in white marble, with only one colour introduced for the columns, pilasters, frieze, pediment, and panels of the base. A variety of marble work of late date, seen at Palermo and Naples, consists of inlaid floral arabesque, of orange, red, and brown marbles, with black inserted into white. It is gaudy, being deficient in repose. Similar work is seen in the monuments at Agra, in India.

2002ee. English Alabaster, if selected free from earthy veins and used where wet would not run over it, though only for interior work, may be better than many stones, and it would keep its colour. Of all building materials it is about the least porous or absorbent. It has been used for monumental work from a very early period, and much delicate work has been executed in it. The inner arch moulding of the west doorway of Tutbury Church, carved into birds' beaks, of the Norman period, is in ordinary alabaster, and remains in good preservation. This material came into general use about the fourteenth century in Derbyshire, and extensively so during the Elizabethan period. Great Britain and Ireland (see MARBLE, 1681 et seq.) contain many varieties of well-known coloured marbles, little used, even at the present day.

2002ff. Memorial slabs of incised marble preceded brasses, and were far superior to them. The English Renaissance produced marble work in chimneypieces equal, if not superior to anything on the Continent. The designs and the marbles were equally good. 2002gg. The Onyx marbles of Algeria, Mexico, and California, of the same nature as Oriental alabaster, can be cut and ground thin enough for window purp ses. At Tarragona Cathedral and at Orvieto are examples of orange-yellow Oriental alabaster. In the east windows of San Miniato are slabs of antique Pavonazzetto, with red-purple markings, nearly two inches thick (par. 615).

2002hh. Carrara and Sicilian marbles are used for steps and floors, wall linings jambs, lintels, columns, capitals and bases, entablatures, altar rails, fonts, pulps, sepulchral memorials, and many other purposes. If consistent details were used, it might probably be employed for public and other buildings (par. 1677a).

2002. A new and beautiful white marble, called Hegge marb'e, from near Brönö, in Norway, is stated to be a pure calcium carbonate, hard, with a few small veins or spots, of nearly uniform whiteness, and taking a high polish. The price in London is about one half that of similar marbles. A green and a red marble are sent from Greece. Verde Antico and Verde di Corsica are composed of limestone, calcareous spar, serpentine, and asbestos.

2002kk. The British Museum, the South Kensington Museum, the University at Oxford, and the Geological Museum in Piccadilly all contain fine collections of coloured marbles, ancient and modern -some wrongly named. The most instructive collection is in the museum of the Louvre. (W. Brindley, Marble: its uses as suggested by the past, read December, 1886, at the Royal Institute of British Architects.)

Mouldings.

2002. A marble to stand exposure to the weather should be close, hard, and vitreous-look ng. Plenty could be selected. The mouldings used in the palaces of the Cæsars and other important buildings in Rome were usually very simple, and mostly consisted of flat hollows and rounds, with small fillets produced out of a chamfer (fig. 662m.). They looked well, and cost less than many modern ones, which are designed forgetful of masons' methods of work. Mouldings needed to be drawn specially to suit the colour of the marble.

2002mm. Marble linings, whenever possible, should be fixed hollow at the back, and a few small places left open in the joints until the solid walls are dry; the hollow allowing the slab to keep warmer than the solid wall, thus avoiding condensation. Good well slaked lime mortar is the best for bedding. Cements are to be avoided. Plaster of Paris should be mixed with a little lime putty, to assist adhesion and prevent swelling. It must be remembered that marbles absorb water by capillary attraction, and are commonly permeable to gases. They absorb water from the mortar, which coming to the exterior surface becomes deposited at the mouths of the pores and gives the surface & brownish discolouration. If the interior surface be coated with asphaltum the discolouration will gradually disappear.

Polishing.

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Fig. 662m.

2002nn. As to polishing marble: properly polished chimney pieces of foreign manufacture, and toilet tables, are rarely found, as acids are used to procure a rapid and cheap, though imperfect and fugitive, result. At the Carrara quarries the marble is first rubbed smooth with fine sand, then with pumicestone, then with two or three stones of variable hardness. finishing off with lead, which gives the last and bri. h est polish. Water and friction do the work. (E. C. Robins.) Marble steps should never be polished, as if properly done they are very slippery and dangerous. In Belgium, only the face of the riser and rather more than half the nosing, stopping just where the foot pitches, is polished. This rom below has the appearance of a completely polished stair, while at the same time there is no danger from slipping. (C. H. Brodie.) Polished marbles and stone rarely go well together in the same work; but some marbles-greys, reds, and cippolinos-look well dull-polished, and then would go better with stone. White marble as used by the Tuscan carvers was not polished.

These full-size illustrations (fig. 662m.) have been taken, by permission, from among the specimens of old marbles in the collection of Mr. W. Brindley.

SECT. IV.
CARPENTRY.

2003. Carpentry is the science of framing or letting into each other an assemblage of pieces of timber, as are those of a roof, floor, centre, &c. It is distinguished from joinery in being effected solely by the use of the are, the adze, the saw, and the chisel, which are the carpenter's tools; whereas joinery requires the use of the plane. See 2102. et seq.

2004. Though necessarily of high antiquity, the very scanty information which Pliny and Vitruvius have left us on the subject would merely show that the science was known by the ancients. The roofs of Egypt present us with no more than flat coverings of massy stone; a pediment roof, therefore, would seem to have been among the first efforts of constructive carpentry; and upon the pitch which this. then and since, has received in different countries, we shall hereafter have to speak. The Greeks appear to have used carpentry in the construction of their floors and some other purposes; but in a country abounding with stone and marble, it is not likely that wood was much used in the interiors of their buildings, unless where lightness, as in doors, for instance, required its employment. With the Romans it was much more commonly used; and from all that can be gathered, we may consider them as the fathers of the science.

2005. Among the moderns it has been very successfully cultivated; and, with very few exceptions, we may almost assert that the works of Palladio, Serlio, De Lorme, Sir Christopher Wren, Perronet, and a few others, exhibit specimens which have scarcely been surpassed in later times, notwithstanding the scientific form it has assumed in the present age. 2006. To the mechanical principles of carpentry we have, in Chap. I. Sect X. of this book, directed the attention of the student; and to the section now under our pen we should have added the words Descriptive and Practical to Carpentry, but that much of what could have been said on that head has already been anticipated in the section on Descriptive Geometry. Hence, in what follows, that which comes under such pred cament will be only given in particular cases, for the purpose of saving time and trouble to the reader in the application of its principles to them. We must, here, also remind the reader, that under the section BEAMS, &c., and TIMBER, have been described the different sorts of timber used for building purposes, their strengths, and the strains to which they are subject and which they are capable of resisting; and that therefore this section is confined simply to putting pieces of timber together, so as to form the assemblage of timbers under which we have commenced by defining the science. To do that properly requires great skill and much thought. Considerable waste, and consequent expense to the architect's employer, result from that ignorance which assigns to the scantlings of timber larger dimensions than are absolutely necessary for the office of each piece; insufficient scantlings will bring the architect into trouble and responsibility; and the improper connection of the pieces will be equally ruinous to his reputation. The principles of practical carpentry are, nevertheless, simple; and though to form new combinations and hazard bold and untried experiments in practice will require all the skill and science of a talented artist, the ordinary routine of carpentering is to be learnt by a little application and a due exercise of common sense.

2007. After these observations, we must introduce the student to the first operation which in practice may arise. It is not every where that timber can be obtained in sufficient lengths to stretch across the void he has to cover; and it will in such cases be necessary for him to know how one piece of timber may be so joined to another, for the purpose of lengthening it, that the two pieces, when joined, may be as nearly as possible equal in strength to one whole piece of timber of the same dimensions and length. This operation is of great service to the builder, and is technically called scarfing. To perform it, the joints are indented, and bolts are passed through the pieces within the length of the indents, such bolts being confined above and below by means of nuts and screws. fig. 663. four ways are exhibited of accomplishing the object in question. A and B are the methods usually employed for joining together plates, lintels, and ties, in which bolts

Fig. 663.

B

In

are rarely necessary; but if such a method is used for scarfing beams, bolts must be employed. The stronger forms, which only should be used for beams, shown in C and D, are not only in that respect such as should, on that account, be used for beams, but are executed without loss of length in the pieces of timber. The length of the joints of the scarfing may be increased at pleasure; the diagrams are merely given to show the mode of doing what was required. With fir, however, when bolts are used, about four times

the depth of the timber is a usual length for a scarf. Scarfing requires great accuracy in execution; for if the indents do not bear equally, the greater part of the strength will be lost: hence it is improper to use very complicated forms for the indents.

2003. Pieces of timber are framed into and joined to one another, by the aid of mortices and tenons, and by iron straps and bolts; and on the proper placing of these depends the soundness of the work. If a piece of framing is to stand perpendicularly, as in the case of partitions, without pressure from either side, the mortice and tenon should be in the centre of the wood. But in the case of framing floors, in which the pressure is on the upper surface, and entirely on one side, the mortices and tenons ought to be nearest the side on which the pressure is, by which the timber will not be so much weakened; and hence it is the constant practice to cut the mortices and tenons as in figs. 664, 665. By the method shown in the last-named figure, the tenon obtains more strength from an additional bearing below, which is further increased by the inclined butment above, called a tusk.

Fig. 664.

2009. The method of framing wall plates together at an angle, for the reception of the hip rafter on the dragon beam, and the angle ties for retaining the wall plates in their places, is shown in fig. 666., wherein AB is the mortice cut for the tenon of the hip rafter

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Fig. 665.

BEAM

Fig. 667.

Fig. 666.

shown in fig. 667.

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C

Fig. 668. is one of the wall plates, showing the halving to receive the other plate, and the cutting necessary for dovetailing the angular tie. Fig. 669. shows the method of cutting the mortices and tenons of principal and hip rafters; another method being given in fig. 670., and to be preferred where a greater resistance to thrust is sought, because by it a double butting is obtained on the tie beam. Inasmuch, however, as in this last case the beam is cut across the grain to receive the rafter, the part left standing to receive the heel of the rafter may be easily split away; to obviate which, the socket may be cut, as at A, parallel to the grain of the wood. cd is the iron strap for securing the rafter's foot to the tie beam, and keeping it in its place. A plan of the upper part of the tie beam is given at B, showing the socket and mortice of the section A in the last figure. C exhibits the mode in which a principal rafter is strapped to a tie-beam, with the joogling.

2010. The most approved method of forming butments (fig. 671.) for the struts or braces, aa, which are joggled into the king-post, is to make their ends, which act against the joggle, perpendicular to the sides of the brace; they will thus be kept firmly on their butments, and have no tendency to slide. C is a section of the king-post and tie beam, showing the mode of wedging and tightening the strap, with a single wedge, in order to draw the tie beam close to the king-post. D is a section of the same parts to a larger scale, and with the introduction of a double wedge, which is easier to drive than a single one, because there is less action upon the cross grain of the wood.

D

c

a

Fig. 671.

Fig. 670.

B

E

2011. Straps in carpentry should be sparingly used. Professor Robison has very properly observed, that "a skilful carpenter never employs many straps, considering them as auxiliaries foreign to his art." The most important uses of them are, that of suspending the tie beam to the king-post, and of securing the feet of the principal rafters to the tie beams in roofs.

2012. Bolts are sometimes used for the last-named office, with washers and heads and screw nuts, in which case the washers, nuts, and heads should be well painted, though

even then they are liable to rust. Wherever the iron work used for securing a system of framing is exposed to the humidity of the atmosphere, it should be rendered durable by frequent painting. Price (British Carpenter, 1759) observes thus: "There is One particular that had liked to have escaped my notice, concerning the placing of iror straps on any truss, thereby meaning to help its strength, which is by turning the end square (as shown at E, fig. 671.). This method embraces the timber in such a manner, to make it like a dovetail, which cannot draw from its place; another observation is, to bolt on your straps with square bolts, for this reason: if you use a round bolt, it must follow the auger, and cannot be helped; by this helping the auger-hole, that is, taking off the corners of the wood, you may draw a strap exceeding close, and at the same time it embraces the grain of the wood in a much firmer manner than a round pin can possibly do." The example given by Price, however, for turning square the strap, is injurious to the rafter, which must be partially cut to admit of it.

FLOORS.

2013. The assemblage of timbers in a building, used for supporting the flooring boards and ceiling of a room, is, in carpentry, called naked flooring, whereof there are three different sorts, viz. single flooring, double flooring, and double-framed flooring. But before entering on the particulars of either of the sorts, we will make some general observations on the construction of floors, which require the architect's attention.

FIRST, the wall plates, that is, the timbers which lie on the walls to receive the ends of the girders or joists, should be sufficiently strong and of sufficient length to throw the weight upon the piers. SECONDLY, if it can be avoided, girders should not lie with their ends over openings, as doors or windows; but when they do, the strength of the wall plates must be increased. To avoid the occurrence in question, it was formerly very much the practice in this country, and indeed is still partially so, to lay girders obliquely across rooms, so as to avoid openings and chimneys, the latter whereof must indeed be always attended to. THIRDLY. Wall plates and templets must be proportionately larger as their length and the weight of the floor increases. Their scantlings will, in this respect, vary to 4 by 3 inches, up to 7 by 5 inches. FOURTHLY. The timbers should always be kept rather higher, say half to three quarters of an inch higher, in the middle than at the sides of a room, when first framed, so that the natural shrinking and the settlement which occurs in all buildings, may not ultimately appear after the building is finished. Lastly, when the ends of joists or girders are supported by external walls whose height is great, the middles of such timbers ought not at first to rest upon any partition wall that does not rise higher than the floor, but a space should, says Vitruvius (lib. 7. c. 1.), be rather left between them, though, when all has settled, they may be brought to a bearing upon it. Neglect of this precaution will induce unequal settlements, and, besides causing the floor to be thrown out of a level, will most probably fracture the corners of the rooms below. 2014. SINGLE FLOORING is constructed with only one series of joists (as shown in fig. 672.). In this way of framing a floor, if a girder is used, it should be laid as nearly as possible over the centre of the apartment. A single floor containing the same quantity of timber as a double floor is much stronger; but the ceiling of the former is liable to crack, and cannot be got to so

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Fig. 672.

good a surface when finished. Hence, where the bearings are long, it is much better to use double flooring.

2015. The scantlings of fir joists for single flooring are exhibited in the subjoined table, and are founded on our own practice.

Length in Feet.

6

8

10

12

14

18

20

The weight of a square varies from 11 to 18 cwt.

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These scantlings may be varied if wanted, according to the laws laid down in the section BEAMS, PILLARS, &c.; 1622. et seq.

2016. In fig. 672. AAA are the joists, and B the floor boards. The laths for the ceiling are nailed to the under side of the joists AAA.

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