Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/522

Rh 470 BUILDING [MASON-WOKE. Mediaeval work. Building in stone more diffi cult than brick laying. Setting stones. Use of mortar Many of the early buildings of the Middle Ages were entirely constructed of masses of concrete, often faced with a species of rough cast. The early masonry seems to have been for the most part worked with the axe and not with the chisel. A very excellent example of the contrast between the earlier and later Norman masonry may be seen in the choir of Canterbury Cathedral. In those times the groining was frequently filled in with a light tufa stone, said by some to have been brought from Italy, but more pro bably from the Khine. The Normans imported a great quantity of stone from Caen, it being easily worked, and particularly lit for carving. The freestones of England were also much used ; and in the first Pointed period, Purbeck and Bethersden marbles were em ployed for column shafts, &c. The methods of working and setting stone were much the same as at present, except that, as the roads were then in a very bad state, and in many places the only means of conveyance was by pack-horses, the stones were used in much smaller sizes. The methods of setting out work were, however, different from those of other styles, as might be expected from the difference of forms. As time went on the art of masonry advanced till, in England, in point of execution it at length rivalled that of any country. From the regular and determined form of bricks, modes or systems for setting or arranging them, may be formed, and any workman, by habit and an exertion of memory merely, may become competent to build a brick wall as well as it can be built, but it is not so with stone used in common masonry walling. The workman in this material has for the most part to deal with masses of all forms and of all sizes, and a continual exercise of the judgment is required from him beyond the tact or skill which may be acquired by practice. For this reason workmen are gene rally less to be trusted to their own discretion in stone building than even in bricklaying. The young mason should be extremely careful to avoid making the beds of stones concave or hollow ; for if this be done, in any case where the stones have to bear much pressure, they will flush or break off at the joints and disfigure the work. The best or highest sort of stone walling is the easiest to set ; it is that in which the stones are all tooled and gauged in regular parallelogramic figures, to range in courses and suit the thickness of the wall to which they are to belong ; and the most difficult to execute properly is that in which amorphous stones are used, the mason being allowed merely to dress them roughly with his hammer or axe, and fit them in as he best can to form the most compact mass : this is called rubble walling. From the brittle nature of stone, great tact is required in setting, to prop or bear up the longer pieces in every part, or they will break across, and thus occasion more injury than could accrue if the whole mass had been made up of small pieces. Very long lengths, therefore, should be avoided, even in regular tooled courses, with which the bearing is or should be perfectly even, and a settling down of the work itself is hardly to be feared. There is a certain medium which may be preserved ; and although the object is obviously, in stone as in brick walls, to form a compact mass, as unbroken into parts as possible, a mason will act judiciously in breaking a very long stone into two or more shorter ones, and working them in that state, though he thus makes two or more additional joints, well knowing that he has the power of counteracting to a certain extent the ill effect of joints made by himself, but that those made by accident are irremediable. The observations made in the section on brickwork, on the use of mortar, will apply here also. Of whatever quality the stone may be of which a wall is to be built, it should consist as much of stone and as little of mortar as possible. If the stone be inferior in durability and power of resisting the action of the atmosphere to the mortar, besides the certain fact that the mortar will yield until it has set hard, and so far act injuriously, no ulterior good is gained ; and if the stone be the more durable material, the more of it that enters into the wall the better. Indeed, in rough walling, if the stones be pressed together until the more prominent angles on their faces come into actual contact, the interstices being occupied by mortar, it will be better than if a thick yielding mass were allowed to remain between them. Absolute contact, however, should not be permitted, any more than in brickwork, lest the shrinking of the mortar in drying leave the stones to such unequal bearing as the prominent parts alone would afford. Stone being generally of a less absorbent nature than brick, it is not a matter of so much importance that it be wetted before setting ; nevertheless, adhesion on the part of the mortar ia more certain and more complete, if the stones be worked in at least a damp state. What bond is, and the necessity for it, have also been Bonding, shown in the preceding section ; and bond is of not less importance in stone walling than in bricklaying. We have also hinted above at the greater difficulty of understanding, forming, and preserving it in the former, and can now only add a few observations in addition that can be of any use, and these with reference to rubble walling particularly. Instead of carefully making the joints recur one over the other in alternate courses, as with bricks and gauged stones, the joints should as carefully be made to lock, so as to give the strength of two or three courses or layers between a joint in one course and one that may occur vertically over it in another. In bonding through a wall, or transversely, it is much better that many stones should reach two-thirds across alternately from the opposite sides than that there should be a few thorough stones, or stones extending the whole thickness of the wall. Indeed, one of the many faults of stone masons is that of making a wall consist of two scales or thin sides, with thorough stones now and then laid across to bind them together, the core being made up of mortar and small rubble merely. This is a mode of structure that should be carefully guarded against. There is no better test of a workman s tact and judgment in rubble walling than the building of a dry wall, or wall without mortar, affords. Walls are frequently built with mortar that without it would have fallen down under their own weight in a height of 6 feet, in consequence of their defective construction, thus rendering it evident that they are only held together by the tenacity of the mortar, which is very seldom an equivalent for a proper bond of stone. Masons are very apt to set thin broad stones on their narrow edges to show a good face, by which the wall is injured in two ways; the practice tends to the formation of a mere case on the surface of a wall, and it for the most part exposes the bed of the stone to the atmosphere, as a stone is more likely to be broad in the direction of its bed than across it. The footings of stone walls ought to consist of the largest Footing stones which can be conveniently procured. It is better to have them of a rectangular form than any other ; and if they are not square, their largest surfaces should be laid horizontally. With this shape and disposition they will make the greatest resistance to sinking. When footings can be obtained the full breadth of the wall in one piece, they are to be preferred ; but if not, then every alternate stone in the course may be the whole breadth. Each course should be well bedded in mortar. Rubble walling is cither coursed or un coursed. In the Hubble latter sort, fig. 5, Plate XXL, the work is carried on with walls, stones of any sizes, as they occur, and without reference to Uncour their heights, somewhat in the manner of the Cyclopean v&amp;gt;( walling of antiquity, the interstices of the larger being filled up with smaller stones. For this work the mason uses no tool but the trowel to lay on the mortar, the scabling hammer to break off the most repulsive irregu larities from the stones, and the plumb-rule to keep his work perpendicular. The line and level are equally un necessary, as the work is independent of considerations