The brick work is started from the top of the
grillage platform with a steel channel curb, three feet in depth,
through which two lines of steel rods are run in each direction, thus
binding together the first three feet of brickwork, and designed to
prevent any flaking at the outside. At a level of three feet above the
bottom of the brickwork, a layer of water-proofing is placed over the
interior area and covered with two courses of brick, upon which are
built diagonal brick walls, 4 inches thick, 12 inches apart, and about
18 inches in height. These walls are themselves perforated at
intervals, and the whole is covered with hand-burned terra-cotta
blocks, thus forming a cellular air space, which communicates with the
exterior air and serves as an insulation against heat for the
steelwork beneath. A single layer of firebrick completes the flooring
of the interior area, which is also flush with the bottom of the flue
openings.
There are two flue openings, diametrically opposite, and 6 feet wide
by 17 feet high to the crown of the arched top. They are lined with
fire brick, which joins the fire-brick lining of the interior of the
shaft, this latter being bonded to the red-brick walls to a point 6
feet below the top of the octagon, and extended above for a height of
14 feet within the circular shaft, as an inner shell. The usual baffle
wall is provided of fire brick, 13 inches thick, extending diagonally
across the chimney, and 4 feet above the tops of the flue openings.
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