Random Rubble (fig. 3) is the roughest form of stonework. It is built with irregular pieces of stone usually less than 9 in. thick, loosely packed without much regard to courses, the interstices between the large stones being occupied by small ones, the remaining crevices filled up with mortar. Bond stones or headers should be used frequently in every course. This form of walling is much used Elevation fe. isis we 1 3E, ;; 3 Esje I, Section RANDOM RUBBLE WALLING-FIG. 3. in stone districts for boundary walls and is often set dry.without mortar. For this work the mason uses no tool but the trowel to lay on the mortar, the scrabbling hammer to break off the most repulsive irregularities from the stone, and the plumb-rule to keep his work perpendicular. Coursed Rubble (fig. 4) is levelled up in courses 12 or 18 in. deep, the depth varying in different courses according to the sizes rlvKv&rcT" and Kentish rag rubble-work is a soft sandstone called “ hassock." In the districts where it is quarried it is much cheaper than brickwork. (For brick backing see BRICKWORK.) Ashlar facing usually varies from V4 to 9 in. in thickness. The Work must not be allwof one thickness, but should vary in order that effective bond with the backing may be obtained. If the work is in courses of uneven depth the narrow courses are made of the greater thickness and the deep courses are narrow. It is sometimes necessary to secure the stone facing back with iron ties, but this should be avoided wherever possible; as they are liable to rust and split the stonework. When it is necessary to use them they should be covered with some protective coating. The use of a backing to a stone wall, besides lessening the cost, gives a more equable temperature inside the building and prevents the transmission, of wet by capillary attraction to the interior, which would take place if single stones were used for the entire thickness. All work of this description must be executed in Portland cement, mortar of good strength, to avoid as much as possible the unequal settlement of the deep courses of stone facing and the narrower courses of the brick or rough stone backing. If the backing is of brick it should never be less than 9 in. thick, and whether of stone or brick it should be levelled up in courses of the same thickness as the ashlar. There are many different sorts of wallin, or modes of structure, arising from the nature of the materials available in various localities. That is perhaps of most frequent occurrence in which W I” either squared, broken, or round flints are used. This, a ug when executed with care, has a distinctly decorative appearance. To give stability to the structure, lacing courses of tiles, bricks or dressed stones are introduced, and brick or stone piers are built at intervals, thus forming a flint panelled wall. The quoins, too, in this type of wall are formed in dressed stone or brick work. Uncoursed rubble built with irregular blocks of ragstone, an unstratified rock quarried in Kent, is in great favour for facing the external walls of churches and similar works (fig. 5).
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