Laboratario National de Engentiaria Civil, Lisbon

Cracking susceptibility is an important characteristic of rendering mortars, as it affects their permeability, their durability and their appearance. Nevertheless, presently it is assessed by empirical, not quantifiable, methods. In fact, it is very difficult to evaluate the tensile resistance of a mortar during the setting and hardening processes and certainly even more difficult to determine the forces induced in the mortar by the restriction of shrinkage, due to adherence to a more rigid background. In this paper an experimental methodology is described to evaluate cracking susceptibility and a classification is established. The special equipment prepared is described. Specific tests are presented, carried out to measure and register forces induced by restricted shrinkage in mortar specimens, to determine their tensile resistance at several ages, to trace the force/displacement curves during tensile tests and to measure free shrinkage since moulding. Classification criteria are established, applied to a set of different mortars and discussed.