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The riving stone, which is a harder and more durable stone, is brought to the
surface in larger blocks and riven with wedges into slabs, dressed on the surface,
?quared, and sold as tooled slabs. The operation is far more difficult than with
the thin lift stones; it will often split in irreglar lines, and cause the stones to
the either hollow or rounding. It is a frequent occurrence to find such stones
when laid, ¼ in. higher than their neighbours, causing a most unsatisfactory and
sometimes dangerous footway.
One of the greatest disadvantages 6f York Stone as a paving material is its
?nequal temper, or, in other words, to find stones of the same degree of hardness,
and when laid it will often be noticed that certain stones will wear more rapidly
than others, causing the surface to present an uneven appearance, and forming
receptacle for pools of water.
One of the best practical tests for the quality and hardness of York Stone is
the rough way in which it has been tooled. A chisel will hardly touch some of
the hardest stones, and soft ones are often dressed quite smooth and regular.
Owing to the hardness of some of the York Stone, the indentations in its
surface are often not thoroughly tooled out, and consequently stones are often
went out full of holes, and, owing to these defects, some of the best and most
Vurable stones are often condemned.
The absorptive properties of York Stone are very much greater than those
of Artificial Stone: no less than 120 cubic feet, or 750 gallons, or 7,812 lb. of
water would be absorbed by the York Stone in a street of average length. It is
?alpable that this must either percolate through and cause the areas adjoining
to be very damp, or to remain charged in the stone, causing it to continue in a
very damp and unhealthy state until it has been given off in the form of vapour
by changes in temperature.
One of the most important duties that devolves upon a public body is to
carry out such measures as will improve the health of their district, and there
than be no doubt that proper drainage of the subsoil, and the making up of
?oads with non-absorbent materials, and laid out at such falls as will cause the
surface water to drain away in the least possible time, has had something to do
with the satisfactory state of health in a great number of the districts in and
around London.
Artificial Stones when laid in position are practically non-absorbent, owing
to their surfaces having been subjected to a bath—in the case of Victoria stone
of a solution of soluble silica, and in the case of Imperial stone of a solution of
silicate of soda, which has a great affinity for the materials of which the stone
?s composed, and which, by induration, causes the surface to become so hard
and compact that it is almost non-absorbent.
Owing to the great absorptive powers of York Stone, it has a tendency to
aminate under severe frost by the expansion of the moisture becoming frozen,
causing the stone to disintegrate.
The average life of York Stone has been estimated at twenty years, but the
wear would be directly as the traffic it receives.
In 1883, Mr. Lovegrove, the Surveyor of Hackney, reported " that flags laid
in 1857 had worn from 1½ inches to 17/8 inches by 1883, giving an average wear
of 11/1 1/6 of an inch in twenty-six years."
In the Strand some Yorkshire flags laid in 1861 were worn out in 1884.*
*Bulnois on Footpaths, lxxxv., Transactions, Inst. Civ. Engineers.