This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
This is a joint fortified against lateral motion by inserting into opposite mortise holes in abutting stones a pin or plug of simple section and hard durable material, and of a size varying more or less with the magnitude of the stones. This is called a dowel, and it is useful in arch work, in the facing of breakwaters, piers, quay and dock walls, piers and abutments of bridges, etc, and is sometimes inserted at every joint. It may be a piece of copper or iron of double dovetail form, but more frequently consists of a slate cube from 4 in. to 1 in. square. Oast iron dowels about 1½ in. thick and double the length are used for the drums of columns, but not so frequently as small slate cubes. For marble work generally copper dowels 2 in. long and ½ in. square are appropriate enough. In all cases the dowel ought to be fairly set and made to fit tightly either by friction or by being fully run with cement, lead, or sulphur, etc. When occurring between the beds of ashlar, a dowel is sometimes denominated a bed-plug and sometimes a bed-dowel-joggle.
Elbow Joint occurs when a crosette is formed, or when a voussoir and part of a horizontal course are cut out of one block.
Face Joint occurs in the face or front, or most important elevation or surface of a structure. It varies greatly in specific designation according to the finish of the visible part, which, for instance, may be either close, chamfered, or pointed. The term is perhaps most frequently used in connection with the face of an arch. In a skew arch of equal thickness from crown to springing the face joints are slightly curved and their chords radiate to a point below the axis.
Fair Joint signifies in face work a joint in the same plane as the rest of the work, both true and square, and generally speaking one executed in a neat, exact, and workmanlike manner, with parallel surfaces out of winding and carefully dressed.
Fair Axed Joint occurs in granite when the beds, joints, and arrises are worked fair, that is to say, true, square, and straight, the stone being axed as well as broached, i.e., dressed fine and close, with the pick or else with a hammer and punch previous to being hewn to a nearly smooth face with the axe. The pick is a heavy hammer with pointed steel tips, and brings the surface of granite simply out of twist or to a fine finish, but not so fine as that wrought by the granite or patent axe, or patent hammer, which, possessing a head consisting of six or more steel cutting edges, about 3 in. in extent, can put the finest possible axing, or dressing, or finish upon it. Granite, to be worked well, requires specially trained masons.
False Joint is made by running a groove to imitate a joint.