Rheology and hardened properties of single-coat render mortars with different types of water retaining agents

This paper compares the effect of two different water retaining agents in single-coat render mortars. The water retaining agent used in the experiments were cellulose methyl-hydroxypropyl and super absorbent polymers with various contents ranging from 0.05 to 0.15 wt.% of the total weight. Properties in fresh and hardened state were investigated. Fresh state properties include theological behaviour, slump and density. Mechanical strength, transport properties through capillary absorption tests and water retaining capacity were measured in hardened state. Results indicate that MHPC promote the cohesion between the material particles in fresh state, increase the cohesiveness and is more efficient in fixing water molecules within their structure but, may lead to lower strength in the hardened state. SAP particles can also be used as water retaining admixtures, although they influence drastically the theological parameters, specially the yield stress, traduced in removing water from the mixture, promoting a decrease on workability. However, the use of a plasticiser can help to circumvent this decrease of workability and, the higher flexural and compressive strength results of SAP mixtures indicate that SAP particles are more efficient to promote adequate water retention, even in adverse conditions. (C) 2008 Elsevier Ltd. All rights reserved.