Kōrero: Building materials

Whārangi 4. Cement and concrete

Ngā whakaahua

Concrete block

Moulded concrete blocks were a cheap alternative to brick masonry and looked a bit like stone. Some were being made in New Zealand in the early 1900s, and a few houses and other buildings utilised them. Firth began the first large-scale production of New Zealand concrete blocks in 1938. Concrete blocks are formed with thin walls, leaving a large cavity in the centre so that reinforcing steel can be placed in the wall. Blocks are made in standard sizes and are joined with a 10-millimetre-thick cement mortar. Concrete blocks proved to be very popular in New Zealand, particularly for industrial buildings, because they allow walls to be rapidly built.

Precast concrete

Entire buildings can be almost all made using concrete frames and floor panels precast in a factory. Very often, precast elements are an important part of the architecture of the building. Precast elements are made in high-quality reusable moulds, with steel reinforcing placed in the mould before pouring the concrete.

Terrazzo

Terrazzo is a special form of precast concrete in which the aggregates are specially selected for their colour and shape, and the cement mix is coloured to obtain a material which is highly decorative. It was widely used in the 20th century for floors in commercial and institutional buildings, as well as for such things as domestic sink benches. Following the casting and curing process, the material is machine-ground to obtain a robust, smooth, fine-grained finish. In the early 2000s terrazzo enjoyed a resurgence of popularity as a high-quality architectural finish.

Tonnes of cement

 

Limestone deposits close to rail links or deep-water ports were ideal for cement manufacture. They were quarried at Whāngārei, Tarakohe in Golden Bay and Milburn in Otago. The names Golden Bay and Milburn became synonymous with cement. In the mid 2000s cement was produced at only two plants – one at Cape Foulwind, near Westport, the other at Portland, near Whāngārei. Their combined output was over 1 million tonnes per annum.

 

Konka board

Konka board was developed in the early 1900s as a lightweight panel system which had some of the virtues of concrete. Concrete for the panels used volcanic pumice as an aggregate, and had a backing of building paper. Panels were about 900 by 900 millimetres, and 50 millimetres thick. They were fixed into timber framing with galvanised steel clips and nails. Joints were covered with hessian (sacking) soaked in wet cement and the whole surface was then roughcast.

Asbestos cement

In the early 1900s asbestos was combined with cement to form thin rigid sheets suitable for cladding and lining for buildings. It could be moulded and it naturally lent itself to use for roofing, including large corrugated sheets known as ‘super six’, with matching spouting and flashings. It was also sold as a large slate for roofing and wall covering. Marketed as a long-lasting lining, it was widely used – especially by home handymen.

In the mid-1970s, asbestos’s link with the lung disease asbestosis was recognised, and it is no longer used in buildings. Where it is found in existing buildings, the law requires it to be professionally removed in strictly controlled conditions. A substitute for asbestos cement is fibre cement, formed with reinforcing fibres of cellulose or glass.

Me pēnei te tohu i te whārangi:

Jeremy Salmond, 'Building materials - Cement and concrete', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/building-materials/page-4 (accessed 28 June 2019)

Story by Jeremy Salmond, published 11 Mar 2010