Buarr.— On the Building Materials of Otago. . 1538 
Durability is a property to which concrete lays special claim, and, I 
think, with good reason, for it increases in strength with age, while most 
other materials commence to deteriorate from the moment they are put into 
the building. Lime, which is of a perishable nature, enters into the ecom- 
position of cement concrete, but, as the proportion is so small, seldom 
exceeding ten per cent., and as the lime is protected by the silicates and 
other durable ingredients that are in combination with it, the deleterious 
acids of the ocean, or atmosphere, can have little effect on the mass. 
The advantages of cheapness, strength, dryness, and many other good 
qualities to which conerete lays special claim are not like those already men- 
tioned ‘‘ constant quantities.” They depend so much on locality, cost of in- 
gredients, and skill in construction that no general comparison can be 
established between it and other materials for which it is a substitute. 
The chief drawback to the use of concrete is the difficulty of ensuring 
good materials and workmanship, and the risk thereby incurred. From the 
peculiar nature of the work, the margin of safety is very small. There is 
only one step from absolute security to utter failure, and that step may 
consist of a simple act of carelessness-in selecting or mixing the materials. 
It is popularly supposed that any ordinary labourer can build a concrete 
wall ; but, such is not the case, the amount of skill and attention required, 
particularly in house-building, is equal, if not greater, than that demanded 
from the tradesman. 
In addition to marine works, for which it is pre-eminently suited, con- 
crete has, within the last few years been applied to an infinitude of purposes 
ashore. In England it has-been used for pavements, causewaying, and 
water-pipes, as well as bridge-building and ordinary architectural and orna- 
mental works. Paris has thirty-two miles of sewers, and thirty-seven miles 
of an aqueduct in concrete. The latter is the most extensive work of its 
kind in existence. There are nearly three miles of arches, some of them 
being fifty feet in height and forty feet span. 
The village of Vescuit, near Paris, has a Gothic Church entirely of con- 
crete, in one piece from foundation to spire, and the lighthouse at Port Said, 
eighty feet high, is of the same character. 
Concrete is either built in blocks previously moulded, and laid like stones 
or bricks, or in what is called the monolithic system, which consists in lay- 
ing the soft ingredient between frames in the position they are ultimately 
intended to occupy. The former is undoubtedly the better, as it does away 
with the risk of using faulty materials ; but the latter is much cheaper, and 
on that account is more generally adopted. The simplest form of blocks is 
that of common bricks; in England these are manufactured in large quan- 
tities by machinery, and form excellent building materials. A compressed 
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