Light Straw Clay
Light straw clay is a mixture of straw and clay slip, primarily used to fill the spaces in timber frame constructions.
Light straw clay combines the advantages of natural materials with modern insulation standards. The maximum wall thickness of 30 cm (12 inches) ensures optimal drying and prevents moisture problems. Particularly impressive is its flexibility in application: The material can be either applied directly in its plastic form or pre-formed into blocks and panels. Light straw clay shows its particular strengths in renovation work, especially in timber frame infill.
A Look into History
The development of light straw clay began in the 1920s in Germany, inspired by the traditional wattle-and-daub technique. After World War II, this building method gained importance in Europe as it met increasing energy requirements through improved thermal insulation.
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The term "Leichtlehm" (light clay) was first used in 1944 in the German Earth Building Code and encompasses a broader range of aggregates. The light straw clay technique is one variant of this building method.
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Important impulses for modern application came in 1983 through Franz Volhard's standard work "Light Clay Construction: Traditional Material - New Technique" and in the 1990s through Robert Laporte's further developments in the USA.
The Material
The base consists of a clay slip made from clay subsoil and water, which is prepared to a slurry-like state. The main component is straw, which is mixed with the clay slip. The density and thus the insulation effect can be controlled through the mixing ratio: Less clay slip increases the thermal resistance (R-value), while more clay slip enhances the thermal mass.
Building Method and Application
Light straw clay walls are built within a timber frame structure. The construction process involves several steps:
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Construction of the load-bearing timber frame
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Installation of formwork between the spaces
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Dense filling with the light clay mixture
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Immediate removal of formwork
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Drying phase with walls open on both sides
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Final plastering of the dried walls
