Artificial ageing by salt crystallization: test protocol and salt distribution patterns in lime-based rendering mortars

Abstract Salt weathering is one of the main damaging factors that affects old renders, much owed to their particular characteristics and to the diversity of salt sources available. Salt tests are usually used to experimentally study this topic. They enable to predict the susceptibility of repair or replacement materials and, hence, to improve the durability of interventions. This paper proposes an artificial ageing protocol that provides specimens suitable either to assess the susceptibility of a given mortar to salt damage as well as to simulate old mortars to be used in further experiments. A second aim of this paper is to analyse the artificial ageing caused by this protocol on a set of lime-based mortars with the characteristics of those usually found in the topcoats and undercoats of old renders. It was found that the water transport behaviour and the salt distribution patterns are markedly distinct in topcoat and undercoat mortars, with significant impact on their salt crystallization resistance.