Agriculture Reference
In-Depth Information
Figure 101
Placing the voussoir
into precise position
checking against the
line from the profile
tree to the striking
point. (Courtesy of
John Bryn)
point then the intrados positions would be established on the turning piece and
lines strained between them and the profile tree to guide the setting of the vous-
soirs (Fig. 101).
The porous rubbing bricks which were kept dry during all stages of prepara-
tion were now soaked in a tank of clean water, to a point just short of satura-
tion. This was to ensure that in laying the voussoirs would not dry-out the lime
putty: silver sand mortar too quickly, allowing time for the joints to be applied
and prepared, and each voussoir precisely positioned; ensuring good bond
strength for the overall arch. To produce joints of such fine measurements
for gauged work, it was important that the slaked putty lime, of the preferred
Greystone (feebly hydraulic) lime, was brought to a fine state of division by
screening it through a suitably sized mesh. It was run into either a dampened
cut-down timber barrel, then used for the general walling mortars or into a
specially made shallow 'dipping box'; placed hip-high on a stack of bricks to
reduce bending. Some craftsmen would add a small amount of screened sil-
ver sand, but as some limes slaked to a consistency that could be a little gritty
this would be accepted as fine aggregate. This 'fine stuff', as it was sometimes
referred to, was prepared to suit the size of the joint desired, which was gener-
ally to the consistency of whipped cream. Throughout the whole laying proc-
ess it would be periodically stirred to maintain this consistency and the top of
it levelled-off to facilitate applying the bed joint to the voussoir, which for the
typically fine joints was done by dip-laying. This process of picking-up the putty
joint involves floating the voussoir on the top of the levelled mortar so that the
brick's bedding surface just contacts the mortar and sufficient adheres to it to
form a full joint.
