Internal Retrofitting with Hemp-Lime on Brick Masonry : a Study to Prevent Damage Caused by Sodium Sulphate

In Sweden there are a great number of neo-gothic churches built in brick masonryaround 1870-1910. They are constructed as massive masonry walls with façadebricks attached to a core of massive red bricks. In the majority of these churchesthere is a presence of sodium sulphate causing salt damages. The source of the salts is known to be the red masonry bricks and the damage occurs both internally and externally on the walls. Damages occurred already after a couple of years after the churches were built and ever since they caused expensive renovations with little or no durability. As the sodium sulphate crystallizes inside the plaster the damages cause spalling of the surface.Since 2016 a method to prevent or delay salt damages has been studied and evaluated. By adding a layer of insulation on the internal wall the microclimate on and nearby the plaster surface can be changed and the damages caused by crystallization decrease. When adding an insulating layer made by hemp-lime plaster before adding the lime plaster the salts cause less visible damage to the internal plaster.Full-scale test surfaces have been made both in the laboratory and inside twochurches. After two and three years respectively, there are no visible salts causingdamages inside the churches, where salts previously came back directly after eachrenovation. In the wall in the laboratory at Lund University the bricks where contaminated with sodium sulphate and internally rendered with hemp-lime plaster with a lime plaster surface finish. Even though there are lots of salt-related damages externally there are thus far, more than two years after construction, no signs of any damage internally