Agriculture Reference
In-Depth Information
Figure 177
The completed oculus.
Case Study: Practical Testing of Historic and Modern
Rubbing Bricks
Rubbing bricks, and particularly those made from fine-graded and washed
brickearths, are soft in comparison to all other building bricks. Fired to a point
just below vitrification (900ºC/1652°F), the brick possesses no fireskin, com-
mon to other fired bricks. Despite their softness and absence of a protective
fireskin, these bricks are extremely durable.
Before such bricks are used, they are first soaked in clean water to enable
them to pick up a fine mortar joint (1-3 mm) without the mortar rapidly dry-
ing out. When the brickwork is finished off, some weeks later, by rubbing
smooth with an abrasive, hand-held, float-stone, it has been observed that a
thin veneer forms over the surface of the brick, which is fairly hard to breech.
Further hardening occurs over a longer period of time (several months) as the
brick dries out, affecting its outer face.
The performance of modern rubbing bricks compared to their historic
counterparts is important in terms of both conservation works and informing
future production of such bricks. To these ends, a series of tests and analyses
were carried out on a selection of historic and contemporary rubbing bricks.
Practical Testing in the Cutting of Historic and Modern
Rubbing Bricks
The practical testing of rubbing bricks was undertaken to assess and compare
how easily and quickly each one rubbed and cut. Rubbing was carried out on
