Earth buildings

By - , Build 96

Earth is truly the ubiquitous building material, making earth buildings seem an obvious option for early settlers. However, its use was limited.

This rammed earth house built in 1989–92 by Barry James, near Tasman, has load-bearing clay walls.

Although it only required very simple tools, earth construction does not appear to have been the first choice for early New Zealand settlers. Brett’s Colonists’ Guide (1883) does not even mention it. Preferred alternatives like raupo or wood were widely available and had many advantages.

Nevertheless, earth was commonly used for creating fireplaces and chimneys, and blocking out drafts from between the boards in timber houses. The Maori tradition of piling earth on the side of the wooden whare for warmth was used into the late 19th century.

The arch-enemy of earth construction is water, whether falling as rain, rushing past the building as a stream or just wicking up from the ground. Its presence, whether due to accident or abandonment, can lead to the short-term deterioration or long-term ruin of earth construction buildings. Consequently, almost all surviving old earth buildings are in places with relatively low rainfall.

Turf construction simplest

Internationally, earth was seen as the ‘poor man’s stone’. There are four generic earth constructions – turf, adobe, cob and pisé.

The simplest approach was to cut pieces of sod or ‘turf’ from the ground, and assemble them into walls. The walls could be covered with a clay plaster ‘weathercoat’. The sod could even cover the roof – the predecessor of todays ‘green roofs’. These were the most temporary earth buildings, possibly because they included minimal off-site materials so the roofs did not keep the destructive water off the walls.

Adobe blocks sun-baked

Adobe construction (from the Spanish adobar – to plaster) uses sun-baked, but unburned, earth blocks. Chopped straw or grass is added to clay, or low-clay earth with sand is used. Water is added to make a sticky mass which is then thrown into open-bottom moulds. Once dry enough not to slump, it is removed from the mould and set to dry in the sun. Shrinking occurs as the block dries out – not after it is assembled into the wall. The completed wall can be plastered, often with a mud or lime wash.

Cob more common

For cob construction a mixture of earth, straw and water was ‘puddled’ – often by a packhorse walking in a circular trench into which the materials were fed. This mixture was then thrown down on to a brick or stone basecourse, to be trodden and compacted by the workers. The wall rose at about 18 inches (45 cm) a day, depending on the labour and speed of drying. Like the other earth constructions, this was a fair-weather job, more suited to spring and summer.

Pisé like cob but rammed

Pisé followed the basic approach of cob but differed in three important aspects.

1. It used earth mixed with small pebbles, although clay was also available.

2. The mix was dry (or slightly moistened) rather than wet.

3. The mixture was placed into removable wooden moulds and rammed hard with the pisoir.

Pisé construction can be readily identified by the regular holes through the wall, where the ‘putlocks’ hold the two sides of the moulds together against the pressure of the earth as it is being rammed. Again the surfaces could be plastered, although the decorative finish from the mould surfaces can be left largely untouched.

The most famous New Zealand pisé building is Pompallier House, Russell, Bay of Islands, which was built by Marist priests in 1842. Nowadays modern technologies – mechanical diggers, steel moulds, tapered bolts, powered compactors and damp-proofing – have made pisé construction easier, although the need for skill remains.

This rammed earth house built in 1989–92 by Barry James, near Tasman, has load-bearing clay walls.

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This rammed earth house built in 1989–92 by Barry James, near Tasman, has load-bearing clay walls.