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.