The influence of hydroxyalkyl methylcellulose on early skin formation in cement‐based tile adhesive

The effect of cellulose ethers (CE) with same water retention (WR) level but different molecular weight on the early skin formation of cement adhesive mortars was studied. In drymix mortars CE provide WR higher molecular weight and dosage of CE both improve WR. In this study all CE concentrations were adjusted to provide same WR independently from molecular weight of CE. Adjusted concentrations were obtained from zero‐shear viscosities measured in aqueous CE solutions.

Measurements with cement‐based mortars identified the interstitial pore solution viscosity to determine WR level. Data show comparable WR for equal interstitial pore solutions, independently from the molecular weight of the CE if its concentration was adjusted accordingly. However, for cement adhesive mortars formulated with CE having different molecular weight which all provide equal WR, early skin formation was found to vary notably. Higher dosed low molecular weight CE outperforms CE with lower dosage but high molecular weight. This effect can be explained through the formation of a CE containing layer upon evaporation of water from the water‐air interface of the mortar.