Poultices and mortars for salt contaminated masonry and stone objects: Fid-Bau Portal

Poultices and mortars for salt contaminated masonry and stone objects

Auras, Michael

The success of measures to reduce the salt content of contaminated objects by application of poultices depends on several factors: experiences with different poultice materials, with modifications of their application and with the influence of the specific conditions. Some of these critical factors are the admixture of different clay minerals to the poultice, surface sealing and pre-wetting. Hints for an enhancement of the efficiency of desalination are derived from case studies and from laboratory experiments. Tests to achieve further enhancement of desalination efficiency by applying electrical potential or by addition of water from the backside are described. A sensitive treatment of a salt contaminated painting on wooden panel is also presented. The second part of the paper is concerned with the suitability of different mortar systems for repointing or rendering. The pros and cons of cementitous mortars of high porosity and reduced capillarity versus hydraulic lime mortars with high capillarity are discussed in the light of practical experiencein building preservation and maintenance. Porous cementitious mortars with waterrepellent admixtures have frequently been used over the last 30 years. If moisture supply from the masonry is low, they can maintain an intact surface for a long time. Several cases are discussed where new damage occurred after a couple of years. An alternative is the use of lime mortar which works as sacrificial mortar or plaster. Due to its high capillarity moisture and salt aresoaked into the lime mortar which ultimately deteriorates by salt crystallization. If the strength of the lime mortar is enhanced by natural hydraulic components or by compaction during application the service life time of such a hydraulic lime mortar can reach decades even with extreme salt load. Research on desalination poultices and on lime mortars in the last two decades, as well as practical experience, have led to a wide variety of materials for desalination and building maintenance. A thorough analysis of the specific situation and the careful In: Lisbeth M. Ottosen and Inge Rörig-Dalgaard and Poul Klenz Larsen and Isabelle Brajer and Peder Bollingstoft and Mette Marciniak and Maja Svane (eds.) (2008): Salt Weathering on Buildings and Stone Sculpture. Proceeding of the conference in Copenhagen 22-24 October 2008, Danmarks Tekniske Universitet DTU, S. 197-217