Agriculture Reference
In-Depth Information
rubbers needed to be soaked, but not saturated, a judgement that came with
experience, but in essence they would be left under water until the water
stopped bubbling and making a 'sizzling' sound, which varies with the density
of the rubber. Left too long and the dipped rubber would not pick up the mor-
tar to form a joint, yet if removed too early and dry it would pick up too much
mortar that would stiffen before the brick was bedded into position.
Lime-Putty Mortar and its Preparation
To produce joints of such fine measurements the substance of the bedding
material must be reduced to a very fine state of division. In normal gauged
work slaked lime, known as putty, mixed with silver sand are the materials
employed.
Precision in the cutting of gauged arch voussoirs, allowing them to lock
together in a very accurate and close-fitting manner, provided strength for the
element, so a low strength mortar, based on a non-hydraulic chalk-lime binder
could suffice. Generally, though as Hammond (1875, 45) emphasises 'Gauged
arches, as a rule, are set in grey lime putty, brought to the consistency of cream'.
Hammond's old term of 'grey lime' refers to the feebly hydraulic class of
lime, a highly workable lime capable of an internal set and long-term carbon-
ation. Sometimes written as 'greystone', 'grey chalk' or 'stone lime', it was the
favoured building lime, especially in the city, since the seventeenth century.
Walker (1885, 14) emphasises the correct choice of building lime, warning:
Mortar used by the bricklayer is made either from stone lime, lias or Portland
cement .…Chalk lime should not be used, as the only setting that takes place in
it is the formation of a surface crust, bearing a small proportion to the bulk….
Stone or gray chalk lime, as it is sometimes called, is generally used…
In reference to setting gauged work, Walker (1885, 63) states:
Stone lime should be used for setting, as chalk lime is not fit for out-door work.
Putty for gauged work would normally be prepared in a galvanised tank by part
filling it with clean water (fit for drinking) and gradually adding lumps of fresh
quicklime to slake it. In the initial stages the water would bubble and boil furi-
ously; this reaction being slower with greystone limes than the purer chalk, or
high-calcium, limes. The whole mass stirred continually with a Larry (a special
tool like a hoe) until it was a thick creamy fluid. The slurry would be passed into
another tank at a lower level through a finely meshed sieve. Richards (1901,
39) states 'the joint should be
1
⁄
32
[1 mm] only in thickness, hence the sieve
should be at least 400 to the square inch'. Once this phase was completed the
