Agriculture Reference
In-Depth Information
Figure 173
A newly built camber
arch with projecting
'keystone', with the
temporary timber and
'G' cramps in place.
The setting-out pins for
the intradosial positions
of the voussoirs are still
clearly visible on the
timber 'turning piece'.
(Courtesy of Jeff Day)
just 'off the arris' with traditional brick jointers of a blade width to suit these
narrow joint sizes. We had been taught that if we laid the bricks correctly and
neatly we wouldn't necessarily need to clean or rub up the to finish the arch
faces; and this proved to be true. We had an occasional slight fingerprint of
lime on a brick face from the gloved hand during laying. As directed we let
this dry and removed it easily with the gentle action of diluted white vinegar
applied with a soft-bristled toothbrush.
Within our contract, we also had to build two circular blind 'oculi', or
'Bullseye' arches. These were to be built, with the bricks cut to voussoirs by
Hugh Tusting, to match the other arches. This was quite a challenge as it had
different elements from the arch construction that needed to be considered to
construct the oculi accurately.
First a timber centre was constructed to the exact size of the inner circumfer-
ence, or soffit, of the oculi. This was marked with two centre lines both vertical
and horizontal, and also a centre or 'striking point' with a small nail. Both ver-
tical and horizontals marked centre lines gave four points of accuracy around
the profile. The voussoirs were then dry-bonded using 3 mm spacing. With four
points of accuracy only a quarter of the circle had to be bonded before reach-
ing a centre line, which of course was the key brick centre.
With our voussoirs laid around the centre we made two trammels, both of
which, fitted over the nail at the striking point; one for the inner circle and
one for the outer circle. The larger trammel would assist the accurate scrib-
ing the standard face bricks to be cut and then checked with it as the invert to
receive the lower half of the oculi.
To radiate and mark the positions of the dry-bonded bricks we devised a tree
similar to that used for the camber arches. We shaped a piece of hardboard
in to a 'U' shape around three sides of the dry-bonded oculi. This enabled us
