Variability of in-situ testing on rendered walls in natural ageing conditions – Rebound hammer and ultrasound techniques

Abstract

External renders are the first barrier against degradation agents and their performance affects directly that of building façades. During the life cycle of renders there is a progressive reduction of their performance until they are no longer able to fulfil their required functions, such as protection of walls and finishing of surfaces. The evaluation to understand how a render performs over time is a complex activity, not only due to the multiple factors concerning its exposition, but also to the difficulty in assessing the in-service behaviour. The use of in-situ techniques gives the possibility of obtaining the information about in-service performance of renders.This paper discusses the use of ultrasound and pendulum rebound hammer techniques for assessing the mechanical performance of rendered walls under natural ageing conditions. The results of ultrasound pulse velocity and rebound hammer index, in conventional and industrial renders, allowed identifying some of the main influencing factors, related both to the rendering-wall system (characteristics and degradation) and the inspection conditions and procedures. This study has confirmed the usefulness of these in-situ tests to evaluate the mechanical performance of rendered walls, despite their variability in natural ageing conditions.