Masonry

Iron in Stonework.

The use of iron dowels or cramps in stonework, unless entirely and permanently protected from oxida tion, is attended by the gravest risks; for upon the expansion of the iron by rusting the stone may split, and perhaps bring about a more or less serious failure in that portion of the building. A case in point is that of the church of St. Mary-le-Strand, London, where the ashlar facing was secured to the backing with iron cramps ; these were inefficiently protected from damp and many of the blocks have been split from rusting. Smeaton in his Eddy stone lighthouse used dowels of Purbeck marble.

Stone Arches.

Stone arches are very frequently used both in stone and brick buildings. (See ARCH ; for general definitions and terms see BRICKWORK.) Stone Tracery; Carving.—The designs of Gothic and other tracery stonework are almost infinite, and there are many methods, ingenious and otherwise, of setting out such work. Nearly all diagrams of construction are planned on the principle of geometrical intersectiois, and the jointing is a matter which must be carefully considered in order to avoid any waste of stone or labour.

Ordinarily in stone tracery the joints should be "mason's joints"; that is to say, the moulding is stopped and returned, the joint being at right angles to a member when it occurs in a straight part of a member and, when it occurs in a curved member, being a continuation of the radius or the mean of the continuation of the two radii. In stone-work the joints are not "scribed" or

"mitred" as in joinery. All the upper construction of windows and doors and of aisle arches should be protected from superincumbent pressure by strong relieving arches above the labels, which should be worked with the ordinary masonry, and so set that the weight above should avoid pressure on the fair work, which would be liable to flush the joints of the tracery.

Stone carving is a craft quite apart from the work of the ordinary stonemason, and like carving in wood needs an artistic feeling and special training. Carving-stone should be of fine grain and sufficiently soft to admit of easy working. The Bath stones in England and the Caen stone of France are largely used for internal work, but if for the exterior they should be treated with some chemical preservative. Carving is frequently done after the stone is built into position, the face being left rough "boasted"—and projecting sufficiently for the intended design.