This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
49. Rubblework is used for rough masonry, as in foundations, backing, etc., and frequently consists of common field stone, roughly dressed; but whenever possible, quarried rubble should be used, as better bedding can thereby be secured. Conglomerate and slate stones abound in many locations, and are cheap and durable, but do not cut easily. They are often used with good effect in walls with cut-stone or brick trimmings; or, when good lengths can be had, for rock-faced sills, lintels, and trimmings.
Fig. 18 represents a good rubble wall, the stones being bonded about every 4 or 5 feet, as shown at a; the largest and best stones should be placed at the bottom, and at the angles, as indicated at b, laid up in alternate courses of headers and stretchers. Such work is generally laid with beds and joints dressed but very little, the rough angles only being knocked off; the stones are set irregularly in the wall, the interstices being filled with spalls and mortar. If better work is desired, the joints and beds of the stonework should be hammer-dressed. The walls are frequently pointed with colored mortar, showing raised joints.
50. Fig. 19 shows a form of rubble masonry much used for country and suburban work. The quoins, or corner stones a, are hammer-dressed on top and bottom, and may be either cut stone or rock face; the last harmonizes well when there is similarly dressed stone in the body of the wall. All the joints should be hammer-dressed, as shown at b, and no spalls should show on the face, while the mortar joints should not exceed 1/2 inch to 3/4 inch in thickness. This makes an effective wall, especially for country churches, lodges, and other small buildings; but the work is expensive, owing to the labor required in dressing the joints.
51. Small boulders and field stones are often used for walls in rustic buildings. An example is shown in Fig. 20. Such a wall should be quite thick, and it is well to use a backing of split stone, to better bond together the boulders.
52. Fig. 21 shows a rubble wall with brick quoins, or corners, as shown at a. In this case all the top and bottom joints of the rubblework have level beds, as at b. This makes a very effective wall, and can be built quite cheaply when the stone used splits readily, or can be laid on its natural bed, thus requiring but little dressing.
Coursed Rubble. In walls of this sort, some effort is made to produce a coursed effect, using stone of random sizes; little or no attention, however, is paid to uniformity of height in the different courses. For such walls, the stones are generally roughly dressed by the mason before he begins work. Care should be taken to get as nearly parallel beds as possible, and to bring the* face of each stone to a fairly even surface at right angles to the beds. The quoins, or corner stones, in coursed rubble are usually dressed and laid with more care than the remainder of the work, and also serve as gauge courses. Coursed rubble, when well built, makes a very solid wall, and is much used.
Fig. 22 represents a coursed rubble wall, a showing the rubble work; b, the quoins; c, the bond stones running through the walls; d e f and d' e' f', two of the course joints.