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.
A rustic joint, described below, being grooved or channelled affords a good example of what may be done by recessing the joints and making them a bold characteristic feature of the work. The only valid reason why mortar joints in masonry are not more frequently sunk or recessed is that a certain amount of weathering is lost by the process, the question of economy being altogether swallowed up by that of effect.
Rough-tooled Joint occurs between surfaces roughly picked or axed, or rough chiselled with the broad axe or boaster, by which they are batted over at a constant inclination to the edge of the stone, or the surfaces may be dressed with the ridges and channels left at irregular distances. In mediaeval times the bed joints of the drums of columns were frequently left rough-tooled, and a uniform bearing obtained by running them with lead. Custom varies now, however, in different localities, but usually the above or a similar kind of dressing is confined to the margin drafts, the superfluous stone within them being simply knocked off until all parts of the surface approximately coincide with a banker rule laid upon it. The kind of work bestowed on beds and joints generally depends on that on the faces. If these are polished, then there is an inclination to introduce lead into the joints, or else they are worked so smoothly as to endanger the loss of the mortar hold. Ashlar beds and joints are usually drafted or boasted, or, in other words, dressed with a chisel called a boaster, 2 inches wide at the cutting edge, which leaves the surface covered with marks like ribands or small chequers at regular distances apart, the drafts being tooled very neatly to allow the stones almost to close at those parts.
Rubbed Joint is a polished, cleansed, or smooth joint, and is described under the latter term.
The stones of cornices and pediments are sometimes run with white lead, that is to say, white lead made into a semi-liquid consistency with linseed oil is poured into their joints. Slate dowels and joggle joints are similarly run with Portland cement grout. There can be no doubt that grout is useful in thus treating the joints of key stones, etc, where the mortar cannot be well and evenly spread, but its indiscriminate use tends to loosen rather than bind and consolidate. All run joints in masonry should be fully run and well filled in. Copper or bronze ties, cramps, plugs, and dowels are preferable to iron, but involve additional expense, though cast iron, with its original skin intact, is little deteriorated by rust, and is often employed in good work for cramping and dowelling. Neat Portland cement of undeniable quality is perhaps the best material in which to fix and embed iron. Wrought-iron ties, however, bedded in masonry - and often of superlative use - should be invariably protected with a coating of zinc or pitch, or some other anti-corrosive. There should be no excuse for concealing this invaluable metal in an unprotected state in the heart of a stone wall to work havoc by corrosion or disfigurement by discoloration.
Rustic or Rusticated Joint is an ornamental finish given to a face joint, particularly in basements of important buildings, banded architraves, arch work, etc. It is effected by sinking, or grooving, or channelling the joint by chamfering, rebating, or moulding the arrises, as shown respectively in Figs. 12, 19, and 20. The chamfered joint forms a right angle, and that which is rebated is called a square joint. Sometimes the grooves or rustications are restricted to the horizontal joints, but as often as not vertical grooves accompany the horizontal. In minor buildings quoins, either plain or rockworked, show rusticated joints. The width of the grooving is quite a matter of taste. Columns not unfrequently have deep, thin, and square rustics, for obviating or more or less concealing flushed joints or edges.