181. To properly lay out, detail and specify the stonework in a building, it is necessary to have a thorough knowledge of the different tools and processes employed in cutting and dressing the stone and of the different ways in which stone is used for walls, ashlar and trimmings.
The following description of different classes of work, supplemented by critical observation in the stone yard and at the building, should give one a good idea of the ordinary methods and practices employed in this Country :
Stonework, such as is used in the superstructure of buildings, may be divided into three classes : Rubble, Ashlar and Trimmings.
182. Rubble Work is only used for exterior walls in places where suitable stone for cutting cannot be cheaply obtained. There are some localities which furnish a cheap, durable stone that cannot be easily cut, such as the conglomerates and slate stones. These stones generally split so as to give one good face, and may be used with good effect for walls, with cut stone or brick trimmings.
Fig. 60 - Rubble, Undressed, Laid at Random.
Fig. 60 shows the usual method of building a rubble wall above ground. After the wall is up the joints are generally filled flush with mortar of the same color as the stone, and a raised false joint of red or white mortar stuck on, to imitate ashlar. Such work should be specified to be laid with beds and joints undressed, projections knocked off and laid at random, interstices to be filled with spalls and mortar. If a better class of work is desired, the joints and beds should be specified to be hammer-dressed.
Fig. 61. - Random Rubble with Hammer-dressed Joints and no Spalls on Face.
Fig. 61 shows a kind of rubble work sometimes used for buildings, which is quite effective for suburban architecture. It should be specified to have hammer-dressed joints, not exceeding ½ or ¾ of an inch, and no spalls on face. This is generally expensive work.
Fig. 62 shows a rubble wall with brick quoins and jambs.
Occasionally small boulders or field stone are used for the walls of rustic buildings. In such case the wall should be quite thick, with a backing of split stone, to hold the boulders, and the exact manner in which the wall is to be built should be specified. There are several kinds of rubble used in engineering work, but the above are about the only styles used in buildings.
The outside facing of a wall, when of cut stone, is called ashlar, without regard to the way in which the stone is finished. Ashlar is generally laid either in continuous courses, as in Figs. 63 and 64, or in broken courses, as in Fig. 68; or without any continuous horizontal joints, as in Figs. 65 and 66, which represent broken ashlar. Coursed work is always the cheapest when stones of a given size can be readily quarried, as is usually the case with sand and limestones. The cheapest ashlar for most stones is that which is cut into 12-inch courses, with the length of the stones varying from 18 to 24 inches. When the stones are cut 30 inches to 3 feet in length, and with the end joints plumb over each other, as in Fig. 63, the cost is considerably increased, and if this kind of work is desired it should be particularly specified.
Fig. 63. - Coursed Ashlar.
Fig. 64. - Coursed Ashlar.
Fig. 63 is regular coursed ashlar, each course - inches in height, and with plumb bond. When the courses of stone are of different heights it is called irregular coursed ashlar.
A form of ashlar now much used is that shown in Fig. 64, in which a wide and narrow course alternate with each other. Six and 14 inches make good heights for the courses.
Fig. 65. - Broken Ashlar (Six Sizes).
Fig. 69 shows regular coursed ashlar, with rustic quoins and plinth, which is much used in Europe.