Agriculture Reference
In-Depth Information
We then took detailed measurements of the gauged arch and the surround-
ing face brickwork feature of a projecting three course platt band directly above
the crown of the arch, as it was before any taking apart. This was clearly impos-
sible with the original arch as it was incorrectly rebuilt. This particular building
was symmetrical in design with an identical window opening at the opposite end
with an arch of the same span, rise, bonding detail, etc; and this was used as a
datum point for all measurements. All the surrounding face brickwork measure-
ments where also checked against the second arch, such as gauge height to Platt
band and the measurement of its projection from the face line. Photographs
were also taken before any remedial work commenced, which are very useful
for a number of reasons. Firstly as a reference to the original arch when rebuild-
ing. Secondly in any contractor/client dispute after the work is complete, and
finally for our portfolio of work.
Measurements were double-checked, photographs taken, then face brick-
work above the arch was carefully taken down. This area consisted of some of
the projecting Platt band up to the stone cill of the first floor window opening.
This was laid in an approximation of English bond with an oversized header on
the header course, centralised below the opening. The header courses mainly
consisted of 'snapped headers' with less than a quarter being full tied-in head-
ers. Regretfully the majority of these bricks had to be discarded due to previ-
ous damage and replacements were found from a local reclamation yard in
Bow, East London. These were very slightly oversized to the originals, but the
closest match that could be obtained, so they were decided on and laid with
slightly tighter joints to compensate; and the appearance was most satisfactory.
On a large sheet of 18 mm plywood we set out the geometry of the arch. We
drew a horizontal 'springing line' and marked off the width of the opening. By
geometry we then established a vertical centre line at 90 degrees to this, some-
thing Gerard was always keen to stress the importance of, both in setting out
and constructing an arch. The 'rise' was then measured on top of the spring-
ing line onto the centre line, to true underside of the segmental arch - with
no allowance for the 'blocked' key bricks - and a line was then drawn from this
down to the 'springing point on either side to form a chord. By geometry we
then bisected the chords with arcs scribed above and below them, allowing us
to scribe straight lines through the bisected arcs terminating on the centre line,
to establish the 'striking point', or radial centre of the segmental arch. The arch
could now be drawn and the voussoirs marked.
From the detailed measurements and drawing of the arch, a timber centre
was constructed from 18mm WBP plywood for the structural formwork. The
positions of the key bricks were drawn and then the centre was then cut out.
To allow the projecting key bricks to step down, small cut-outs of the correct
depth were required to be accurately set out into the top of the centre. Flexible
6 mm WBP ply was then wrapped around the top of the centre at a width of
