Other Materials in Short Supply
Other Materials in Short Supply
Stocks of other building materials were not particularly good at the outbreak of war, and inevitably the upsurge of defence construction work led to scarcities.
Where New Zealand depended on imported supplies, the slowing up of imports created real difficulties, and such small reserve stocks as had been set aside before the war became of vital importance.
We have noted that imports of corrugated iron, after totalling over 20,000 tons in each of the 1936 and 1937 calendar years, had fallen to 13,000 in 1938 and were at 16,000 tons in 1939. A reserve stock for defence buildings had been set aside by the Public Works Department, but was only about three-quarters of the estimated requirement for emergency mobilisation buildings alone. Other stocks of corrugated iron were abnormally low when war broke out.
Then, in 1940, imports of corrugated iron, at 9000 tons, were well under half of 1937 arrivals. Worse was to follow. For the rest of the war imports averaged only 2250 tons a year, about one-ninth of 1937.
Corrugated iron soon became very scarce. Its use was severely restricted throughout the war and for some years after. It was, in fact, one of the principal causes of restrictions on private building. Wartime imports of galvanised flat iron were well below normal, the annual inflow averaging less than half the pre-war amount. Malthoid-covered roofs and, later, wooden gutters became a visible evidence of wartime shortages.
Imports of window glass had fallen away before the war, and stocks at the outbreak of war must have been below normal. In this case, however, imported supplies arrived in fair quantities throughout the war, and extreme shortages did not develop.
Stocks of gypsum, essential in the making of cement and plaster,1 page 249 were good when war broke out and imports were well above prewar levels for most of the war years. Imports of plaster of paris, however, fell right away, until at the lowest point, in 1942, only about 1 per cent of pre-war supplies arrived. Here local production was expanded to help fill the gap.
Most of New Zealand's pre-war cement requirements were locally produced, and imports of cement were trivial by comparison with local production. The building and construction industry continued to rely almost entirely on local production throughout the war years. Production in 1939 had reached 231,000 tons but declined, to be close to 215,000 tons, for each of the years 1940, 1941 and 1942, after which it returned to 1939 levels. With increased requirements for defence works, restrictions on the use of cement became for a time a severe limiting influence for less essential works.
Some of these shortages of materials were to continue well after the rush of defence construction work was past. There were, for example, shortages of cement in the second half of 1945, and, as late as November 1945, the use of corrugated iron was not permitted on new buildings, galvanised flat iron could be used only for door and window flashings, and similar restrictions applied to a number of other materials.
Portland cement may be defined as the product obtained by intimately mixing together calcareous (containing lime) and argillaceous (containing alumina), or other silica, alumina, and iron oxide bearing materials, burning them at a clinkering temperature, that is a temperature at which partial fusion occurs, and grinding the resulting clinker, The powder so produced possesses the property of combining chemically with water to produce a hard or ‘set’ mass. This chemical combination takes place very rapidly if no ‘retarder’ is incorporated with the cement.
Gypsum (calcium sulphate) is the material generally used for this purpose, and it is customary to add from two to three per cent to the clinker during the grinding operation.
Plaster of Paris Gypsum (calcium sulphate). Dry plaster is gypsum which has been heated until about one quarter of the original water remains.