Issue 35 autumn 2022 - Flipbook - Page 55
junction of the column shaft and column bases to protect
against ground water penetration and therefore improving
the longevity of the replacement stones while maintaining
the historical precedence. Once approved the drawings
were issued to the different quarries for manufacturing
the new pieces.
half columns, and further temporary works to support the
frontispieces to allow the removal and replacement of the
ground to 1st floor fluted columns. The local Bletchingdon marble, which the original columns had been crafted
from, was no longer available with the quarry having
closed many years previously. This meant a lengthy
process of material sampling had to be undertaken to find
a suitable alternative, which also had to be approved by
the Oxford City Planning Department and Historic England. Eventually the carboniferous limestone, Swaledale
fossil was identified as the preferred replacement. The
chosen stone was subjected to an extensive laboratory
testing schedule and the results were used to prove the
suitability of the stone by our in house design department
in line with relevant design codes. A similar sampling
process was carried out to select the correct material for
the Cloister paving with Purbeck Wetson Bed and
Crosland Hill chosen, and for the general repairs and repairs to the frontispieces, Clipsham Medwell was selected.
As can often happen when working with historic and
fragile structures, when the existing frontis fluted columns
were removed, it was found that the pilasters directly behind them had also deteriorated beyond restoration and
had to be replaced. On site templates and moulds were
taken and the pilasters were replaced using Clipsham
stone from the Medwell quarry.
The fluted frontis columns and pilasters were manufactured by Stamford Stone and delivered to site as loose
pieces at one thirds heights each. Once the temporary
works were installed and signed off, replacement could
take place by fully dismantling a column and its adjacent
pilaster and then re-building them with new stone before
moving on to the next column and pilaster.
The chosen stone for the colonnade columns and half
columns, Swaledale Fossil, is sourced from a quarry which
has restrictions on the size of the blocks. Due to this the
decision was made to split the column into three pieces
mirroring the existing condition in order to achieve the
column heights. This was done by using the base (naturally bed), shaft (turned vertically off bed) and capital
(naturally bed) to achieve the required height. The full
and round columns were manufactured and pre-assembled by Dunhouse Quarry Ltd and delivered to site as
single units in specially designed timber pallets. Preassembly consisted of internally pinning the base, entasis
shaft and capital together to form a complete column.
Once the temporary works were installed and signed off,
replacement could take place in a hit and miss manner,
i.e. remove and replace columns 1, 3, 5 & 7 before
removing and replacing columns 2, 4, 6, & 8.
All the columns, full round, half round and fluted frontis
and the pilasters were surveyed dimensionally and
templates taken where required. The information was
drafted up in house and issued for approval to the design
team to include the introduction of lead DPC’s at the
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Conservation & Heritage Journal
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