[SUSTAINABILITY IN PRACTICE] This ancient material has plenty to offer the 21st-century designer, says Sandy Patience
Unfired clay materials have excellent sustainability credentials, offering very low embodied energy, high recyclability, and low waste. Typically used internally, they can also provide a high degree of environmental control, through humidity and temperature regulation.
Unfired clay brickwork is an ancient construction material that is still common in the 21st century, particularly in hot climates, where there is a vernacular of soft clay dried in the shadow of the sun. Unfortunately in contemporary Europe, traditional hand-made bricks lack the tolerances that are required for narrow-profile walling, typically 100mm thick.
This shortcoming has led some brick manufacturers to set up production lines for unfired clay alongside those of their fired clay cousins, in a bid to tighten dimensional tolerances. This also helps to guarantee consistency of material content. The result is that unfired clay has become a practical alternative to more commonly specified materials.
In design terms, thin-walled unfired clay brickwork is best considered as non-structural weak masonry, best for internal applications. It is ideal for use in monolithic walling and partitioning, as its poor compressive strength and fragile relationship with water make it unsuitable for most structural uses. There are examples of buildings with thicker loadbearing earth walls, but these use more material and reduce usable space.
Finishes for unfired clay brickwork should be vapourporous, such as clay board, clay and lime plasters, vapour-permeable paints, and limewash.
Ironically, it is unfired clay’s relationship with water that gives it one of its most attractive attributes - its capacity to buffer relative humidity by absorbing moisture from the air at high humidity, and releasing it at low humidity.
This, together with the material’s ability to offer easily accessible thermal mass, make it attractive for designers who want to combine a sustainable material with a non-mechanical solution for indoor air management.
Sandy Patience is an architect and editor of greenspec.co.uk
Clay board, an alternative to gypsum plasterboard, is suitable for drywall applications including walls and ceilings. It can be applied to either timber or metal studwork, and then completed with a coat of clay finishing plaster.
Size 20mm or 25mm thicknesses
Composition Clays, silt, sand, plant fibres, straw, hemp, reed and hessian mesh
Clay Two-Coat Plaster
Clay plaster is a practical alternative to gypsum-based plasters - and it resembles them in appearance. Available in a range of naturally pigmented colours, the Clayworks brand of plaster can obviate the need for a paint finish.
Composition Clay, sand, hemp, straw and natural pigment
Configuration Undercoat and finish coat
Thickness applied Undercoat: 15mm; finish coat: 3mm
Compressed Clay Block
Produced by a company specialising in unfired clay, this block has thermal and relative humidity-regulating properties. The block can be finished with clay plaster, as well as other breathable finishes.
Size 295 x 140 x 100mm
Composition Unfired clay and aggregate
Configuration Smooth, unperforated
Compressive strength 5N/mm2
Ecoterre Earth Brick (standard)
Also available in a larger size, with either profiled or smooth surfaces, Ecoterre bricks provide thermal mass and acoustic insulation, and regulate relative humidity. Bricks can be finished with clay and lime plasters, clay boards and certain paints.
Size 220 x 105 x 67mm
Composition Unfired clay
Configuration Vertically perforated, profiled for render or smooth
Compressive strength 3.8N/mm2
Naterra Clay Block
Unfired clay is used as a binding agent and to facilitate extrusion of the composite blocks. The blocks are dried using waste heat, giving them a low embodied energy, and they are made of at least 50 per cent recycled plasterboard.
Size 440 x 220 x 100, 110 or 120mm
Composition Unfired clay and recycled plasterboard
Configuration Horizontal perforation, interlocking profile
Compressive strength 3N/mm2
Weight Approx 18kg
Sumatec Earth Block
The blocks are ideal as an internal leaf of exterior walls or as internal partition walls, especially where there is a need for a good acoustic wall with high thermal mass. Blocks can help inhibit condensation and regulate relative humidity.
Manufacturer Lime Technology
Size 215 x 215 x 100mm
Composition Unfired clay
Configuration Vertically perforated
Compressive strength 5N/mm2 (or 3N/mm2 if perforations laid horizontally)