Choosing mortar compositions for repointing of historic masonry under severe environmental conditions

Abstract eng:
The quality of repointing work in historic masonry is to an important degree determined by the composition of the repair mortar. Apart from this good workmanship is a basic requirement for durable repointing.Over the past decades awareness has grown that the mortar composition of repointing should always be considered and applied taking into account the hygric and mechanical properties of the existing adjacent materials. Often this is easy enough to realize. However, choosing the composition of a repointing mortar there are situations where various damage risks seem to point at opposing materials properties.In the paper this problem is approximated analyzing a number of damage cases with the aim to define more precisely which requirements and to what extent should be maintained. Subsequently, from lab studies and experiences with the application of natural hydraulic lime (NHL) in specific repointing projects a set of requirements is proposed. The context of this repointing study is repair of low-strength historic fired clay brick masonry in the coastal area of the Netherlands; environmental conditions: sea salt laden, heavy rain load and freeze-thaw cycling.

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