Bond strength performance of mortar coatings in masonry prisms under applied displacements

Abstract In coating systems, mortars must exhibit sufficient deformability to accommodate variations from structural loads, differential movements, and thermal cycles, ensuring adhesion to the substrate. This study evaluated the effect of applied displacements on masonry prisms under compression on the tensile bond strength of mortar coatings. For this purpose, prisms were constructed using two vertically perforated ceramic blocks (290 × 140 × 190 mm), laid with 10 mm mortar joints and coated with three mortar types (mixed, industrialized, and stabilized), employing a plastering mortar layer, with rolled slurry. After curing, the prisms were subjected to compression until displacements of 2 mm, 3 mm, and 4 mm were reached and subsequently loaded to failure. At each displacement level, the tensile bond strengths of the coatings were determined. Based on the acquired data, the prisms’ modulus of elasticity, resilience, and toughness were estimated from the stress–strain curves. The results showed that the mixed mortar coating, due to its higher deformability, provided greater resilience and lower influence on the modulus of elasticity of the prisms, resulting in a less pronounced reduction in bond strength (27.4%) at the highest displacement, compared to the industrialized (34.8%) and stabilized (37.3%) mortars, which exhibited reduced capacity to accommodate displacements without debonding. The higher modulus of elasticity of the industrialized mortar limited deformation absorption, leading to brittle debonding and lower prism resilience and toughness. These findings underscore the importance of selecting an appropriate mortar to ensure the performance and durability of coating systems applied to masonry structures subjected to deformations.