Render-induced cracking of earth masonry

The increasing awareness of the environmental impacts of construction materials has resulted in an increasing interest in earth masonry in the UK in recent years. The use of traditional vernacular techniques has raised the profile of earthen architecture but wider impact is likely to come from commercially produced, thin-walled, earth masonry as a replacement for blockwork, brickwork or timber-framed non-structural internal walls. Earth masonry is susceptible to changes in moisture, and this paper investigates the potential for early-age cracking from changes in moisture content during the most critical period for these materials, namely during construction. It is shown that internal stresses generated by moisture-driven expansion after rendering may exceed masonry flexural (flexure-induced tensile) capacity leading to premature wall failure. This failure mechanism was observed in a test panel and has potential to occur in real walls. Recommendations on how to minimise the risk of early-age cracking are presented.