Agriculture Reference
In-Depth Information
red rubbers, they excavate and initially prepare their clay at their Faversham
works in Kent, transporting it to the Pitsham yard by lorry. Their red rubbers
are available in six colours - light orange through medium to plum red in col-
our - to suit various architectural applications. They also continue to provide
yellow and gault cutters out of their on-site clay reserves.
The raw material from Faversham is approximately one metre deep below
topsoil; once excavated, and weathered over winter, it is milled, washed clean
of impurities and allowed to settle in pits next to the pug mill and allowed
to mature for approximately twelve months. In preparation for moulding the
clean rubber clay is then placed in a pugmill and then conveyed by belt to the
hand-moulding bench.
The wooden moulds - of box, beech, or teak - are dipped in water and
sanded ready for the clot of clay to be thrown once it has been rolled in the
same moulding sand. The green-moulded bricks are then removed for open
stacking in covered hack sheds to dry naturally in readiness for firing. This
takes about six to eight weeks, during which the rubbers shrink by about 11%.
Lamb and Sons have two types of kilns available for firing rubbers - two tra-
ditional downdraught kilns and three modern batch fibre kilns, all fired by
propane gas. The downdraught kilns had a capacity of 30,000-40,000 bricks,
and the batch kilns have a capacity of between 5,000 and 12,000 bricks. Tradi-
tionally, the old downdraught kilns would have contained out of their total
capacity, some 10-15% of rubbers, these placed for four courses maximum in
the centre bolt of the mid-kiln position, the overall burning temperature rang-
ing from 980ºC to 1,140ºC during a 72-hour cycle. The kilns would then be left
to cool for seven days or more before the wicket was removed and the rubbers
were drawn from the kiln.
In the modern computer-controlled batch kilns the full capacity and con-
tent of between 5,000 and 12,000 units can be entirely rubbing bricks. These
stacked inside in a block set formation. The firing temperature, dependent
on the type and colour of rubber/cutter required, will be in the range 980ºC
to 1,060ºC over a 48-hour period; with a greatly reduced cooling time vary-
ing from as little as 8 up to 18 hours. Shrinkage is about 1% and wastage is
minimal.
Today Lamb and Sons TLB rubber range come in two degrees of firmness; soft
rubbers for traditional carving and harder rubbers (cutters) which are intended
for in-house machine cutting and moulding incorporating hand finishing.
In either respect Lamb and Sons have responded to the present-day market
conditions, whereby the lack of site crafting skills increasingly demands pre-
pared gauged elements for on-site assembly only. They therefore offer a ser-
vice of surveying details and providing designs for the specials and carved units
with CAD packages. Machine cutting and moulding is achieved with bench-
mounted disc-cutters and reverse-moulded carborundum wheels through which
