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 term is applied to a square, semicircular, angular, or otherwise shaped tongue and groove joint generally of equal depth the full way through, excepting at the face, near which it abruptly stops in order that it may be concealed. It is the common method by which the sides or ends of stones, or parts of them, are united in balconies, architraves, landings, etc, and is shown in Fig. 16, the joint being run with lead, or flushed up with cement or plaster. The same appellation is likewise given to any joint in which a stone or metal dowel is used, and such dowel is occasionally termed a dowel-joggle. In some cases the joggle is formed by cutting equal and opposite jogs or notches in two stones, filling the cavity with pebbles, and running with cement.
Lap or Lapped Joint is formed whenever one end, edge, or side overlaps another, and is, as has been previously observed, the very essence of bond. Ashlar masonry, worked with alternate headers and stretchers, should be well bonded and lapped. Voussoirs likewise. Stone steps, when not rebated, usually form a lap joint with one another 2 in. deep.
A piece of 5 lb. or thicker milled lead has been often used in columns and arch work, the size of the bed joint, less a width of about 2 in. from the outside, and in mullions, etc, when the beds are very small, to within half an inch from the same. The idea is that the lead yields to the irregularities of the beds, and conduces to a more even distribution of pressure. In turning the arch of the Grosvenor Bridge, Chester, a good deal of lead was skilfully used between the arch stones in plates, wedges, and strips to guard against the joints opening. There is, however, no compulsion as to its use, and the practice is not to be recommended, simply because the same quality which enables the lead to accommodate itself to one alteration of form of an arch ring may, when not cleverly disposed, and under some unexpected concatenation of circumstances, enable the arch to assume another form more at variance with the curve of equilibrium. The same considerations apply with equal force to stone columns.
Mason's Joint is formed by leaving an angular projection to the mortar similar in section to the letter V. The name of this letter is in consequence sometimes applied to the joint, which requires to be made with good mortar to be durable.
Mastic Joint is made by using mastic for the cementing medium. Mastic is an oleaginous cement composed of linseed oil, powdered brick, burnt clay, or limestone, and litharge, the latter constituting about six or seven per cent, of the mixture. It is not so durable as Portland cement, to which it has almost quite given way, but it admits of being painted as soon as applied. Blocks of hewn stone used for ridging were formerly sometimes set with it.