The joints between one block of stone and another are formed in many ways by cramps, dowels and joggles of various descriptions, several of the most common of which are illustrated in figs. 8-16.
The stones of copings, cornices and works of a similar nature, are often tied together with metal cramps to check any tendency of the stones to separate under the force of the wind (figs. 9 and io). Cramps are made of iron (plain or galvanized), copper or gun-metal, of varying sec tions and lengths to suit the work. A typical cramp would be about 9in. long, i or I sin. wide, and from a to -sin. thick, and turned down about I sin. at each end. A dovetailed mortise is formed at a suitable point in each of the stones to be joined and connected by a chase. The cramp is placed in this channel with its turned-down ends in the mortises, and it is then fixed with molten lead, sulphur and sand, or Portland cement. Lead shrinks on cooling, and if used at all should be well caulked when cold. Double dovetailed slate cramps bedded in Portland cement are occasionally used (fig. so).
Dowels are used for connecting stones where the use of cramps would be impracticable, as in the joints of window mullions, the shafts of small columns, and in similar works.
There are many ways of making a joggle joint. The joggle may be worked on one of the stones so as to fit into a groove in the adjoining stone, or grooves may be cut in both the stones and an independent joggle of slate, pebbles, or Portland cement fitted, the joggle being really a kind of dowel. The pebble joggle joint is formed with the aid of pebbles as small dowels fitted into mortises in the jointing faces of two stones and set with Portland cement; but joggles of slate have generally taken the place of pebbles. Portland cement joggles are formed by pouring cement grout into a vertical or oblique mortise formed by cutting a groove in each of the joining surfaces of the stones. What is known as a he-and-she joggle, worked on the edges of the stones themselves, is shown in fig. 12.
Plugs or dowels of lead are formed by pouring molten lead through a channel into dovetailed mortises in each stone (figs. 13 and 14). When cold the metal is caulked to compress it tightly into the holes.
The saddle joint is used for cornices. and is formed when a portion of the stone next the joint is left raised so as to guide rain-water away from the joint (fig. 7).
Two forms of rebated joints for stone copings and roofs are common. In one form (shown in fig. 6) the stones forming the coping are thicker at their lower and rebated edge than at the top plain edge, giving a stepped surface. The other form has a level surface and the stone is of the same thickness throughout and worked to a rebate on top and bottom edges. In laying stone roofs the joints are usually lapped over with an upper slab.
Four forms of jointing for the battering stonework of spires are shown in fig. 15. A is a plain horizontal joint. B is a similar joint formed at right angles to the face of the work. This is the most economical form of joint, the stone being cut with its sides square with each other ; but if the mortar in the joint decay, moisture is allowed to penetrate. With these forms dowelling is frequently necessary for greater stability. The joints C and D are more elaborate and much more expensive on account of the extra labour involved in working and fitting.
Where a concentrated weight is carried by piers or columns the bed joints are in many cases formed without the use of mortar, a thin sheet of milled lead being placed between the blocks of stone to fill up any slight inequalities.
The working of mouldings in stone is an important part of the mason's craft, and forms a costly item in the erection of a stone structure. Much skill and care is required to retain the arrises sharp and the curved members of accurate and proportionate outline. As in the case of wood mouldings, machinery now plays an important part in the preparation of stone moulded work. The process of working a stone by hand labour is as follows: The profile of the moulding is marked on to a zinc template on opposite ends of the stone to be worked; a short portion, an inch or two in length, termed a "draught," is at each end worked to the required section. The remaining portion is then proceeded with, the craftsman continually check ing the accuracy of his work with a straight-edge and zinc tem plates. A stone to be moulded by machinery is fixed to a moving table placed under a shaped tool which is fixed in an immovable portion of the machine, and is so adjusted as to cut or chip off a small layer of stone. Each time the stone passes under the cutter it is automatically moved a trifle nearer, and thus it gradu ally reduces the stone until the required shape is attained.