Special slabs for cants, or
squint-quoins (Figs. 17 and 18) and angles (Figs. 12, 13, 14, 15, and
16) are manufactured, the angle occurring (if we omit the hexagonals and
take the 18 inch slab) at three-quarters the length of each slab. This
gives a half-slab bond to each course, as on one face of the quoin in
one course will appear a quarter slab and in the course above a
three-quarter slab superimposed upon it, or _vice versa_. Thus are the
walls in Figs. 19 and 20 built up. For openings, the jambs and lintels
(and in window-openings the sill) are made solid with a provision for a
key-hole to the mass of concrete filling behind them. That portion of
the jambs against which the slabs butt has a groove coinciding with a
similar one in the edge of the slab, for the purpose of forming a joggle
joint by squeezing the bedding material into them or by joggling them in
with a cement grout. All the slabs are joggled together in a similar
way.
[Illustration: FIG. 21.-FIG 25.]
The plastic concrete filling or beton which the shells are made to
contain may be deposited between the slabs when any number of courses
(according to convenience) have been built up, and when set practically
forms with the solid work introduced a monolith, to which the face slabs
are securely keyed. With over-clayed Portland cements, which are known
to contract in setting, and with those over-limed cements which expand
(both of which are not true Portland cements), the filling in is done in
equal sections, with a vertical space equal to each section left between
them until the first sections have become thoroughly hard, and these are
then filled in at a second operation.
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