Effects of a water-retaining agent on the rheological behaviour of a single-coat render mortar

The effects of a water-retaining admixture on the rheological properties of a cement-based render mortar were studied. This agent, based on a cellulose ether compound, was introduced in contents up to 0.2 wt.%.Rheological behaviour was studied with a rheometer for mortars using two different speed profiles. First, the step profile allowed observing the variation of g and h parameters with the water-retaining agent content, g and h being directly related to yield stress and plastic viscosity. Second, the dwell profile allowed the study of the rheological behaviour variation with time, particularly the study of structural breakdown and reconstruction phenomena. These phenomena could be followed through the evolution of the hysteresis area in the flow curves. It was also possible to conclude that this admixture has a thickening effect except for low amounts (≤ 0.08%) and that it promotes structural breakdown together with a secondary effect of retarding the setting time.