Gypsum hemihydrate–cement blends to improve renderings durability

Gypsum is a historical binder that was already used thousands of years ago. More recently its employment in construction had a significant growth. It is a binding material being used in masonry as a plaster finish coat. Despite being economical, having good performance and easy application in buildings, its use is limited to indoors due to its solubility. Some efforts have been made to improve its performance in external environment. In that sense, researches advance in the attempt at using several admixtures like epoxy resins, polymers, cements, slags and waterproofing materials. The aim of this work was to investigate the effect of blastfurnace slag Portland cement addition to β-hemihydrate and observe the changes in mechanical properties and microstructure to improve gypsum performance. Results show an improvement of gypsum performance when this kind of cement is added to the mixture and a 3-years rendering exposed to external environment had no changes, indicating that there was no ettringite formation. SEM analysis showed a more compact structure which can result in a water resistant composite.