Gypsum late efflorescence on clay brick masonry (vergrauung).

The presence of gypsum efflorescence appeared more and more frequently during the last decades, this often more than one year after the completion of the masonry. Gypsum is moderately water-soluble and therefore these gypsum efflorescences cannot be removed without intensive cleaning techniques. There is in general a lack of understanding about the cause and the mechanisms of formation for this type of efflorescence. Besides this more fundamental question about the phenomenon, the factors that favour and/or inhibit the development of this type of efflorescence are not well known. 

A first objective is to investigate persistent efflorescence cases by a systematic on-site investigation. Next, a tailored experiment is carried out to unravel the mechanism of gypsum formation upon cement paste carbonation. The obtained expertise forms the backbone for developing a fast and versatile efflorescence test method, which allows assessing the risk of efflorescence. Its application to the masonry components combined with the field survey and cement carbonation studies shed light on the cause of persistent gypsum efflorescence and indicated possible solutions.