The upper surface should be weathered, and horizontal copings should be throated.
On a steep ramp or gable it is necessary to dowel the coping to the wall to prevent it from slipping down the slope, or the same object may be attained by working the coping with a horizontal bed, and of such a depth as to enter the wall, as shown at L in Fig. 146. This is not, however, usually done with every stone, but only at intervals in the length of the coping.
A common construction is to cut the backs of these stones vertically downwards from the point a, so that they are triangular in section (see Fig. 132), but this is not so good a form as that shown at L in Fig. 146; especially in a gable of steep pitch, as the height of the stone would he greater than its base, and it would have a tendency to tilt over when the thrust came upon it.
Fig. 144. Stone String Course.
1 Sc. Copes.
The joints of inclined copings may he rebated as shown in Fig.
146, so that as the wet which gets in at the top of the joint cannot flow upwards in the rebate, it is prevented from entering the wall.
Fig. 145 is the section of a saddle-backed coping; the top, instead of being formed by two plane surfaces as shown, is frequently rounded.
Parallel Coping is one of which the upper and lower surfaces are parallel. Such a coping may be used for gables or ramps where it is laid at an inclination, and therefore a sloping transverse surface to throw the water off is not necessary. A copingl of this kind is shown in section in Fig. 457.
These are sometimes alternately high and low, so as to present a rugged and picturesque appearance (see Fig.
124, p. 43).
The coping of a pier or column is called the Capital, that of a chimney is called the Cap.
Skew Corbel.2 Kneeler or Knee Stone (K, Fig. 132) is the stone at the foot of a coping on a gable or ramped wall. It is sometimes cut off vertically downwards from the point a, but such a construction is objectionable for the reasons given at p. 53 with regard to the stone L. It is better that the kneeler should tail into the wall as shown at K in Fig. 146, so that it has a base much greater than its height, and the rubble above it helps to keep it in its place.
Fig. 145. Saddleback Coping.
Fig. 146. Showing Apex-stone S, Kneeler K, and, Second Quoins ss.
1 Sc. A coping in this position is called a skew. 2 Sc. Club-skciv.
Saddlestone is that forming the apex of a gable; also called Bidgestone and Apex-stone.
Cornices (see p. 8) should project well, so as to protect the wall from wet, and should be weathered and throated.
It is important that sufficient of the cornice should rest on the wall to balance the projecting portion, or it will press unfairly on the front of the wall and be unstable.
Sometimes the stones are left a little high at the joints between them, as at x, Fig. 147. This is called "saddling the joints,"1 and is intended to throw the water off them, but involves much expense in extra labour.
The joints between the stones of the cornice, and also those of the blocking course or parapet above, are often secured by lead plugs (see p. 50).
The cornice may itself form the uppermost member of the wall, or it may be surmounted by a blocking course, by a parapet wall, or by a balustrade.