Agriculture Reference
In-Depth Information
approximately 100 mm. Finally another length of 18 mm plywood was cut and
fixed to the bottom of the centre for rigidity to take the weight of the large
span arch. All was fixed with glue and screws. The completed centre was then
positioned under the arch on vertical timbers against the reveals and strutted
firmly with a diagonal timber bracing. The use of appropriately sized 'folding
wedges' enabled the centre to be adjusted tightly up to the soffit of the arch to
secure the brickwork during disassembly and support the existing voussoirs.
The poorly re-built arch was carefully taken down, working from the key
evenly either side out towards the skewbacks, and the voussoirs, some of which
were badly damaged and chipped, were laid out in order of laying on the ele-
vated bench on the scaffold. The lime mortar was removed from each voussoir
by gentle scraping, and these were then lightly re-rubbed on their faces to
remove 150 years of grime and recent staining as well as determine those
which could be salvaged. Thankfully, as Gerard had predicted, they re-rubbed
quite easily on the large rubbing stone.
Some were too damaged and matching replacements were sourced from
'Solo Park' in Cambridgeshire. The new replacement bricks were rubbed
square, scribed to templet and cut to the voussoir shape. The final task in the
preparation of all the voussoirs was to set out from the templet the positions
of the 'dummy' or false joints to the centre of alternate voussoirs, creating the
appearance of two headers and thus a bonded face. These were cut in to a
depth of 5 mm with a 1 mm-hacksaw blade.
We now prepared the existing brickwork and re-checked the position of the
centre. We positioned two horizontal timber beams or 'profile trees' above the
arch, one directly underneath the Platt band and the second one just above it.
The lower one was to line-in the first third of the voussoirs either side of the
arch that could not be guided from the main profile due to the projection
of the remaining Platt band. The centre line of the opening was plumbed-up
using a large spirit level from the timber centre and marked on to both pro-
files. It was also transferred down onto the diagonal strut bracing the two cen-
tre supports; and deliberately positioned to be at the correct measured distance
down from it for a nail to be fixed for the radial 'striking point'. With two lines
fixed to a nail on the striking point and on up to the profile trees, a joint width
back from the springing brick positions, the skewbacks could be cut to the right
bevel and laid with bond to both horizontal and radial alignment.
The intradosial lines, previously set out and drawn onto the top of the cen-
tre for each voussoir, were now transferred across the full width of the timber
centre using a try-square to ensure all the voussoirs would be set square and
parallel over the arch. These positions were then extended up onto the pro-
file trees, the first 5 voussoirs on either side on the lower profile trees and the
remaining voussoir positions onto the upper profile. To secure these radial
lines small panel pins were nailed into the profiles by the side of each mark,
