The Bond Strength Behavior of Polymer-modified Mortars During a Wetting and Drying Process

Polymer-modified mortars are highly popular for setting exterior tile systems and low-porosity ceramic tiles because they possess greater flexibility and higher bond strengths than conventional mortars which increases cladding serviceability. However, the long-term performance of this application is not completely understood and many pathologies has been reported. The negative influence of water saturation on polymer modified mortar is well documented and this paper investigates the influence that progressive water intake on bond strength by applying pull out tests on several different mortars. Four of those mortars were especially prepared with well known raw materials and concentrations, and three others were ready-made commercial products designed for setting ceramic tile on building facades. The tests were performed during twenty-five day drying period in laboratory conditions after specimens saturation for ten days of immersion in water. The results revealed that: (i) the ready-made commercial and the prepared mortars have similar behavior; (ii) their bond strengths are highly influenced by small increases in moisture content; (iii) moisture content higher than 10% is enough to reduce mortar bond strength by one-half; (iv)during the drying process bond strength increases continuously until reaching values similar to the initial ones.