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Technical Note #01 Thermal Conductivity of Clay Masonry

This Technical Note was developed on behalf of the Clay Brick Association of South Africa in response to a call for data from the CSIR (Council Scientific & Industrial Research).

The Thermal Conductivity co-efficient (k-value or λ-(lambda) value) of a material is specific to that material and it is a measured result of tests conducted in accordance with one of the methods set out below.

Thermal Conductivity is a measure of the heat flow through a homogenous sample of material of a known thickness, when a known temperature difference is applied across two surfaces. The result is expressed as Watts per meter per degree Kelvin.  

Test Methods and Standards

Building materials thermal conductivity is tested in accordance with ASTM C177 by guarded hot-plate apparatus, ASTM C518 by heat flow meter apparatus, and ASTM C1363 by guarded hot-box.

Published independent results

Suppliers have had products tested to the above test methods and the results have been published by independent sources such as the American Society of Heating Refrigeration and Air-conditioning Engineering in the Fundamentals Handbook, and various South African Council Scientific & Industrial Research (CSIR) publications.

The Clay Brick Association has had a number of masonry walling systems tested to ASTMC1363 in the Thermal Test Laboratory in Pretoria. Further testing is planned in order to categorise brickwork by a density range and supply a range of thermal conductivities corresponding.


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