It is possible to classify all descriptions of walls under three heads, as follows: -

1. Rubble.

2. Block-in-cour.se.

3. Ashlar.

1. Rubble, on account of the variety of methods of coursing the stones, permits of the following further classifications: -

Uncoursed Rubble.

Irregular coursed Rubble.

Rubble worked up to Courses.

Regular coursed Rubble. In rubble masonry generally the stones are irregular in shape and size, being dressed on face with a waller's hammer. In the best classes of rubble work the stones are sorted according to their shapes and sizes, and are dressed with the hammer to fit against one another with more or less vertical and horizontal joints, according to the quality of the work. In coarser descriptions of rubble work no selection of stones is made, the stones being placed upon the wall in the positions in which they fit best, the interstices being filled with small stones and spalls - small pieces knocked off rough stones with the hammer when dressing down their faces. Little or no attention is paid to the horizontality of the beds or the verticality of the joints. The degree of regularity in rubble work depends in great measure upon the nature of the stone used. Stones of an intractable nature, such as basalt or stones of a crystalline structure, lend themselves best to rough rubble, while those which work more freely under the hammer are used for the more regular descriptions of rubble work.

As with brickwork, the facings of stone walls are laid first, their positions being indicated by means of strained strings, and the interior or hearting is filled in afterwards, care being taken to bond the whole together by means of through or bond stones at frequent intervals. Hollow spalls within the wall should also be thoroughly filled with spaces, and if there is any suspicion that this has not been properly done a trowel plunged into the work at intervals will reveal the fact. Care should also be taken when building the hearting that all the stones are large and well bedded, and that they do not act as wedges, which would cause the wall to split under its own weight. The quoins are usually formed of large stones more carefully bedded than the rest of the work.

Uncoursed Rubble

In this class of work, which is also known as random, rough, or common rubble, no attempt is made to dress the stones beyond knocking off sharp corners and prominent projections. The stones are laid on the wall at random (see Fig. 204), with no attempt at coursing or at keeping the joints regular, the only tools required being a waller's hammer, a trowel, and a plumb or battering rule, as the case may require.

Stone Walling 423Fig. 204. Uncoursed Rubble , Ashlar Quoin.

Fig. 204. Uncoursed Rubble-, Ashlar Quoin.

In walls of dwelling-houses one bond stone should be inserted for every yard super of the face of the wall, and should run from two-thirds to three-fourths through the wall. Bond stones should not run right through walls of dwellings, as they tend to conduct water to the interior. They should be placed alternately on either face of the wall, and be arranged in zigzag fashion, so as to distribute their effect more thoroughly.

A distinct variety of uncoursed rubble is built of flints, as shown in Fig. 205. Concrete or other firm foundation is formed, and a wooden framework is then built up resting upon the foundation, the standards {Fig. 206) being carefully plumbed. Boards or shutters as they are called when used for this purpose - are placed against the standards. The faces of the flints or popples are polled or split off, and are then laid with the polled face against the shutter. The face work is carried up, preferably in cement mortar, to a height of about 9 inches at a time, and the hearting is filled up in layers of about 4 1/2 inches at a time, and thoroughly flushed up or grouted with mortar, care being taken to make the stone bond together. If a wall of this description is to be carried to any great height, the standards are bolted to the wall, as already shown for concrete walls. The quoins and dressings are usually built of some regular material such as brick or dressed stone, and lacing courses of brickwork or masonry are introduced at intervals of about 6 feet.

Stone Walling 425Fig. 205. Polled Flint Wall & Brick Dressings.

Fig. 205. Polled Flint Wall & Brick Dressings.

Stone Walling 427

Fig. 206.

A variety of uncoursed rubble much used in ecclesiastical buildings is that known as Rustic or Polygonal work, which is illustrated in Fig. 207. In this description of masonry no vertical joints occur and no spalls are used on the face. Stones which occur naturally in shallow beds, such as Kentish rag limestone, are usually used for the face stones of polygonal work, the hearting being composed of brickwork. To fit any stone, such as S (Fig. 207), into position, the angles abc and deb are taken with a bevel and marked upon a stone of suitable size, which is then carefully dressed to the three markings with a waller's hammer, the face being hammer dressed. This is an expensive form of rubble work, as it requires a considerable amount of skill and labour to make the stones fit with a close joint.

Fig. 207. Polygonal Rubble, Ashlar Quoin.

Fig. 207. Polygonal Rubble, Ashlar Quoin.

Irregular Coursed Rubble, Or Snecked Rubble

When stones possess a distinct natural bed which varies considerably in depth, it lends itself very well for the class of rubble known as Irregular or Random-CoursedRubble and more generally as Squared'or Snecked Rubble. This (see Fig. 208) is usually built with the beds horizontal and the joints vertical, although it is by no means essential, depending chiefly upon the amount of labour required in squaring the stones.