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.
Circular Joint is one in which either circular sunk or spherical work occurs. It is made when he and she joggles are of circular or curved profile, or when the bed joints of arch stones are embossed, etc.
This is another name for cramped joint.
This always occurs in granite or other kinds of ashlar facing, where it is from 1/8 in. to 1/10 in. thick, and in ashlar without rubble backing, where it should be throughout about ¼ in. thick, which is sufficient for the strongest work, and little enough to preclude trouble from settlement. To obtain it the beds and joints are dressed true, square, and full the whole depth of the block, or at all events for some distance back, and the chisel drafts round the edges form sharp and straight arrises ; but often the stones are only accurately dressed a few inches back, and the rest chipped away and underpinned, leaving insufficient bearing surface. When set properly, the stone is first lowered on its bed before spreading the mortar to try whether the bed and joints are dressed level and true, and if the stone rests with its face in a true plane with that of the other part of the work, or otherwise correctly. Protuberances, if any, are then marked, the block is removed, superfluities are knocked off, beds and joints brushed and wetted, the mortar bed is evenly and thinly spread with fine mortar to within an inch of the front arris, to leave room for a strip of putty as described under Fine Joint, and then the block once more descends to be well and truly laid and settled in place through the active agency of the mallet. A close joint can be obtained with roughly hewn beds, provided they are carefully and regularly axed or broached, and the front arris chisel dressed. The stone must be set on a continuous cushion of fine mortar or cement, without void or packing, showing a perfectly even thickness on the face, but little in excess of the average thickness throughout the bed. When close joints are thus obtained by dint of careful workmanship, it is another matter to preserve them, and where violent shocks have to be withstood the precautions described under Bolted Joint must be observed. Engineers wisely insist that all masonry, whether ashlar or rubble, exposed to the fury of the waves, should be set with full close-fitting joints, or at all events with joints completely and solidly filled in with good hydraulic mortar, as quick setting as possible compatible with the requisite strength. By such means the evil effects of syphonic action arising from water being forced into the joints are avoided. From these observations it will be seen that weirs require very close joints.
A maximum thickness of from 3/16 in. to ¼ in. is amply sufficient in coursed ashlar for strength and durability, presuming that the beds and joints are properly dressed and smoothed. Block-in-course masonry, with roughly dressed beds and joints, requires a minimum thickness of 3/16 in., consequently a coarse joint in this case exceeds in thickness what would be classed as such in ashlar. All uncoursed rubble masonry is built with joints of irregular thickness, and comparatively much coarser than those above noticed, and the mortar, therefore, of which so much is required, should be of the best possible description. Provided this is the case, and that a pretty average thickness is preserved throughout the work, coarse joints are certainly more reliable than thinner ones permeating a superior class of masonry where the fundamental requirements of properly tooled and levelled beds and joints are merely observed a few inches back from the surface.