An ecology centre in mid Wales has been getting back to basics to offer a vision of building materials for the 21st century.

Work has begun at the Centre for Alternative Technology near Machynlleth to build Britain's first public building from compacted earth.

Instead of concrete, conservationists are using blocks made from rammed earth to develop a modern version of a "mud hut" technique first used 10,000 years ago.

The centre, which deals with thousands of calls each year on "green technology", has also used straw as a house building material.

The latest project to build an Environmental Information Centre will cost £630,000 and will to illustrate how earth walls can be made strong enough to support roof loads.

About 180-tonnes of sub-soil from a quarry at Oswestry, Shropshire, will be compacted in layers to form columns and wall panels four metres high.

'Instant rock'

Moist loose earth is turned into a sort of "instant rock" after it is placed in shuttering and then rammed with a pneumatic tamper machine.

The walls will be plastered externally with lime putty and sand render to prevent them from being washed away in the rain.

The building is designed to operate without producing noticeable carbon dioxide emissions and can be easily levelled at the end of its working life.

'Limecrete'

Other features of the building are foundations made of a concrete substitute called "limecrete" and cavity wall insulation that uses sheep's wool.

Project Manager Cindy Harris said earth provided a locally available and cheap resource.

"Earth buildings can withstand the tests of time and intensive usage," she said.

"There is a growing interest in using more natural building materials, but as yet there are few modern examples of rammed earth technology."

'Green' materials

The earth building blocks are "greener" than concrete because making them does not produce carbon dioxide emissions.

Earth is also highly effective in absorbing moisture from the air, thus helping to control humidity in a building.

The CAT information centre is the first large-scale rammed earth project in Britain since the Department of Scientific and Industrial Research helped build two houses in chalk at Amesbury, Wiltshire, in the early 1920s.

The new building, due to be finished next spring, will be insulated using sheep's wool, another material which has proved its worth over the centuries.