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]

There is, however, a more decided difference between West’s system and those previously in use, for it is marked by the fact that the slabs composing the shell of the whole structure in many cases may be built up before the filling-in is deposited between the slabs, and in none of the other cases can this be done.  In fact, only in the first two cases before mentioned can more than one course of slabs be laid before filling-in of some kind must be done.  Compared with the ordinary method of building in concrete, this system avoids:  1.  The charge for use and waste of wood casings; 2. finishing the face of the work (both inside and outside) after the structure is raised, and, therefore, the bursting-off of the finished face; and 3. the difficulties encountered in working mouldings and other ornaments on the face of the work by the ordinary plasterer’s methods.  It also provides a face of any of the usual colors that may be obtained in concrete, besides a facing of any other material, such as marble, etc., and produces better and more durable work, at the same time showing a saving in cost, especially in the better classes of work; all of which is effected