This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
123. The inspector or superintendent should be very careful to have the work properly done, during erection, both in cutting and setting stone, as an imperfect piece, when once set in place, can only be taken out with considerable trouble. The stones must also be carefully examined, as otherwise many cracked and defective ones may be used, either by accident or design. The qualities of the stone should, in a general way, be similar to those enumerated under "Qualities of Building Stones."
Granite may contain cracks, black or white lumps known as knots, and a brownish stain called sap. If such defects are found, the stone should be rejected, if the importance of the work justifies it. The first mentioned is the most to be guarded against, however. Cracks may be discovered by the absence of the clear ringing sound when the stone is struck with a hammer. Sand holes are frequently found in sandstones. These are bodies of uncemented sand which become dislodged by jarring or by the action of water, producing a pitted appearance and an uneven color. Attention must also be paid to securing uniformity of color, as sandstone from different parts of the same quarry may vary greatly in this respect.
124. Patching is an operation often resorted to by contractors, when a small piece has been broken from a large stone. Instead of using a new stone, the old one is patched by gluing on the spall with shellac, the joint being hidden by rubbing stone dust over it. Rain, however, will render the joint useless by washing out the shellac, so that the patch falls off. There are times when a patch is allowable, as, for example, when a new stone cannot be had without great expense and delay. In such a case, the superintendent may permit it, but care should be taken to put on the spall by inserting it, when possible, in a square hole, or dovetailing it in such a way that it will not become displaced.
125. The most common faults of cut stone are poor workmanship and coarseness of surface. Most builders will naturally avoid any extra work in dressing beyond that necessary to be barely acceptable to the inspector.
Frequently the ends of cornices, belt courses, etc. will not properly match. It should be strictly required that the utmost care be exercised in cutting all similar pieces to the same pattern, and that the abutting surfaces be closely dressed.
Stone window sills are often not wide enough to be covered by the wood sill. This should be guarded against; otherwise, the access of rain will cause dampness in the walls and disintegration of the mortar. The wood sill should overlap the stone one at least 2 inches, fitting closely upon it.
126. Care should be used to have the stone set on the natural bed, with good joints, and not in too small or thin pieces. The bed joints, in ashlar work, should be square to the face of the work, and not less than 4 inches wide at both top and bottom. The proper bonding of the walls, especially the ashlar and trimmings, should be given very careful attention, as well as the placing of lintels, copings, wall anchors, etc.
Another point needing attention is to have the mortar, in joints on which great pressure comes, kept back from the surfaces; otherwise, the edges may chip off. Also, before pointing is done, have the joints well raked out and the pointing mortar laid properly.
Many other precautions for the good performance of the work will doubtless suggest themselves to the careful superintendent.