Agriculture Reference
In-Depth Information
A hooked 4mm diameter threaded stainless steel dowel was resin-fixed in to
the replacement brick. A hole was then drilled in the appropriate position
in the core and filled with lime mortar. The tie brick was then carefully lined
up and fixed in to position. All the replacement bricks were lined up with the
joints of the original work, dry fixing before being dip-laid.
The fixing mortar was carefully prepared and kept in a covered box. First of
all, the lime putty was sieved through a mesh (1.5 mm diameter holes) to remove
any lumps of unslaked lime, stones or other impurities. A small amount of very
fine sand (approximately 10% of the mix) was then added and thoroughly
mixed in. Finally, a drop of linseed oil was added and mixed in. The mix by this
stage had a glossy, smooth and creamy texture. It is well worth the time taken to
prepare the mix very carefully as it is vital to the success of fixing. The addition
of sand helps to minimise any cracking as the work dries out and makes for a
more cohesive mix and the linseed oil increases the plasticity. It is important to
cover the mix to prevent debris dropping into it, especially from those who may
be working on the lift above. Even light traffic on the scaffold causes debris to
drop down, and can ruin a carefully prepared mix, making it impossible to lay to
tight 2 mm joints.
Once the mix was ready and trowelled to a flat surface in the box, replace-
ment bricks were thoroughly soaked in a tub of clean water. Getting the soaking
time exactly right took careful judgement as various factors determined the fix-
ing conditions: the relative porosity of the bricks, the prevailing weather condi-
tions and temperature, and the porosity of the existing background. If the bricks
were too dry, it became impossible to ease them into position and to form a
successful bond with the existing material; if they were too wet they slid about
and caused unsightly smearing. The prepared bricks were dipped into the putty
mix and the mortar was trowelled to an even thickness that allowed it to exude
once compressed. This bead of excess mortar was then carefully cut off with a
sharp small tool, leaving full beds (Fig. 89). There is only a limited time that
the bricks can be adjusted to fit whilst the bed is still pliable. This became even
more of a challenge on the tie bricks, which had to be located into the drill
holes in the core.
A rubber mallet or the end of a lightweight hammer was used to tap the
bricks home and adjust their position, making sure that a regular, 2 mm joint
was achieved. Once a section of replacements had been completed, any gaps
in joints had to be thoroughly filled. A drier mortar was used for this in order
to avoid smearing. Only small sections of replacements could be completed at
a time. The reveals had to be very carefully dismantled and rebuilt due to the
fragile nature of the brickwork in those areas. The extent of cracking and voids
on the right hand side made minor controlled collapses unavoidable.
Measurements were taken of the span and rise of the arch in order to pro-
duce a full size drawing. From this, a voussoir templet was made and the
