Buarr.—On the Building Materials of Otago. 157 
cement to-seven of fine road metal and small stuff from the stone-breaker ; 
none of the metal was larger than an inch each way, and the other 
ingredients were well adjusted. The concrete was not heavily rammed 
like “betou agglomeré,” but it seems to have been very firmly pressed. 
Altogether, it was a first-class piece of conerete, and the greatest difficulty 
was experienced in breaking it up with a wedge and heavy hammer. The 
block measured 24 inches long, 12.25 inches high, and 10.08 inches broad, 
and weighed, when dry, 240 Ibs., the outside being covered with a thick 
coat of rich cement plaster, as it is intended to have in a building. 
The first experiment was to determine the impermeability of the plaster. 
A wall of clay was put round the edge, leaving a square foot exposed ; 
water was poured on, and in three hours about three-quarters of a pint had 
penetrated the surface. 
The whole block being then immersed, it instantly absorbed two and 
~ a half Ibs. more, and in sixteen hours the quantity had further increased to 
four lbs. 
On breaking, it was found that the moisture had permeated every 
portion of the block, and the centre was as wet as the outside. : 
The two samples of concrete thus experimented on were of a very 
superior quality; I have never seen anything to compare with them in 
ordinary work. Although these experiments are very crude, and the 
results much higher than would be obtained from less carefully prepared 
specimens, they go a long way to prove that the property of perfect im- 
munity from damp, to which concrete houses lay claim, is not secured by 
the mode of building usually adopted in Otago, and, I believe, the experience 
already acquired in actual practice, fully supports this assertion. 
I shall now consider the strength of concrete, in order to compare the 
cost of the various materials under description, which I intend to do further 
on. The properties of brickwork being so well known, it has from time 
immemorial been selected by municipal authorities as the standard from 
which to determine the strength of buildings, and there are regulations in 
every town fixing the thickness of brick walls in whatever position they 
occupy. I shall, therefore, adhere to the same standard. 
The following table gives the crushing strength of various kinds of 
bricks and concrete ; but, for the purposes of a more general comparison, a 
few examples of other materials are added. 
Crushing weight per square 
inch in Ibs. 
Brick, weak red oie ae ee 550 to 800 
Brick, strongred ss... aa ise 1100 
Brick, first quality... it au 2000 to 4870 
Ordinary brickwork ... ne ie 390 
