Agriculture Reference
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these limes and to utilise local materials, therefore Stafford Holmes (2006, 20)
is quite correct to say:
It is therefore wrong to omit grey chalk lime from the British and European
Standard on building lime, which should be revised accordingly.
In recent years, due to the lack of knowledge and skills in preparing build-
ing lime, Health and Safety concerns and complex 'method statements' for
site use, has meant that most limes, as either a ready-slaked putty or bagged
hydrate, is purchased direct from traditional mortar suppliers ready for use.
Non-hydraulic lime - also termed 'fat', 'rich' or 'high-calcium' lime - is derived
from pure (95%) calcium carbonate such as chalk. This class of lime being
incapable of setting, only hardening by long-term re-absorption of carbon
dioxide driven off during the burning phase, or 'carbonation', as discussed
earlier, was not favoured on structural gauged work. Non-hydraulic lime could,
and still can be, used on some types of finely cut arches that are in themselves
naturally strong, as well as features contained within standard brickwork such
as aprons and platt bands etc. It can also be the preferred lime on certain
works of conservation where a weaker, sacrificial, lime is desired. It is import-
ant to remember, however, that modern non-hydraulic lime putty is nothing
like that used traditionally. As lime mortar expert Bob Bennett (2007) states:
Grey lime putty and modern pure lime putty are often spoken of as being virtually
the same material and capable of being used in the same way. While the building
Industry used almost all the Grey lime produced, only about 10% of the calcium
oxide produced today goes into buildings. Most of the remaining 90% is used in the
production of steel and in the food industry and therefore conforms to strict purity.
I believe those small differences in the composition of the two materials accounts
for the variation in performance. Burning relatively pure limestone, ranging from
between 98.3% and 99.2% pure calcium carbonate largely produces the material
for modern lime putty. I believe that this modern non-hydraulic lime putty is a
much purer product but is a pale shadow of the old Grey lime putty, which could
set both faster and harder.
By both discussing the mortar for fine arches and for ashlar work with joints of
5 mm (¼ in), Bennett (2007) concludes:
Gauged brick arches produced in the traditional way with joints less than 2 mm
could perform with joints of just Grey lime putty, but modern non-hydraulic lime
putty needs the addition of a small amount of finely graded aggregate with no
particles larger than one third of the joint size. On joints in excess of 5 mm (¼ in)
I believe non-hydraulic lime putty is no longer an appropriate binder. I would
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