Abstract
When fresh mortars are applied on a substrate they lose water by suction and by evaporation, sometimes very quickly, and they start suffering some shrinkage, while simultaneously hardening and getting stiffer. Because they are adherent to a rigid background—the wall—the deformation is restrained, stresses develop in the render and are partially transferred to the background. These phenomena can generate cracks on the rendering and damage on weak or friable masonry. Air lime renders also suffer these actions, even if they react in a different way compared to cement mortars: they sometimes have high shrinkage, although they have also some ductility (comparatively high rupture energy), developing lower stresses. New␣renders to apply on old walls must be mechanically compatible with old pre-existent materials, namely with old masonry: they should not produce damage and they must be able to␣protect the wall for a reasonable period of time.
In this paper a test is described to evaluate the performance of renders concerning restrained shrinkage, results obtained are discussed and conclusions are summarised about compatibility parameters and classification.
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Acknowledgements
This research is developed within the Projects “Development of methodologies for the assessment of moisture effects on ancient walls”— POCTI/ECM/46323/2002 and “Study of compatible mortars for the preservation of the constructed Heritage”—POCI/HEC/57890/2004, both with financial support of “Fundação para a Ciência e Tecnologia” of Portugal.
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Veiga, M.R., Velosa, A.L. & Magalhães, A.C. Evaluation of mechanical compatibility of renders to apply on old walls based on a restrained shrinkage test. Mater Struct 40, 1115–1126 (2007). https://doi.org/10.1617/s11527-006-9209-6
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DOI: https://doi.org/10.1617/s11527-006-9209-6