In the first place, temporary ties, or gauges, connecting the slabs forming the two faces of the wall, have been used, and as soon as the plastic filling-in material has set or become hard (but not before), these have been removed. Secondly, permanent ties or cramps have been used, and, as their name implies, have been allowed to remain in the wall and to be entirely buried in the plastic filling-in material. These permanent transverse ties or cramps have been of two kinds: those which were affixed as soon as the slabs were placed in position, and those which were made to form part of the manufactured slab, as, for instance, slabs of Z or H horizontal section. Thirdly, a small layer of the plastic filling-in material itself has been made to act as a transverse tie by depositing it, when plastic, between the slabs forming the two parallel faces of each course, allowing it (before filling in the remaining part) to set and to thus connect together the slabs forming each face of the wall, a suitable hold on the slabs, in some cases, being given to the tie by a portion of the slab being undercut in some way, as by being dovetailed, etc. As the slabs in this latter system generally have wide bases, they may also be bedded or jointed in cement, and, provided temporary ties be placed across their upper edges to connect the slabs forming each face of the wall together, the space between the faces of the wall may then be filled in with the plastic concrete. All these devices, however, are not of permanent utility; they are only temporarily required (i.e., up to the time that the beton has become hard and formed a permanent traverse tie between the two faces of the wall), for it is manifest that the ultimate object of all slab concrete construction is: (a) To retain and to mould the plastic concrete used in forming the wall; (b) to key or fix the slabs to the mass which they themselves have moulded; and (c) to form a facing to the wall. When these objects shall have been accomplished, there is no further need of any tie whatever beyond that which naturally obtains in a concrete wall. In West's system, however, where the slabs are keyed course to course, any kind of transverse tie to be used during the process of construction, except that used in the starting course, is entirely dispensed with, and the courses of slabs above depend solely upon the courses of slabs below them for their stability and rigidity up to the time that the plastic filling-in has been deposited and become hard between both faces of the wall. [Illustration: CONCRETE CONSTRUCTION]