Relationships between the surface roughness of Brazilian dimension stones and the adhesion to mortars

The effect of different surface roughness for ceramic and metals on their adhesive bond strength is widely studied in the field of tribology, but still little investigated for stone claddings, which are natural and quite heterogeneous materials. The main objective of this study was to investigate the relationships between the surface roughness of ornamental stone slabs and their adhesion to mortars were determined by TBS tensile bond strength tests, including observation of types of failure in each test. Slabs with different roughness of the migmatitic stone, commercially known as in Brazil "Jacarand ' a Rosado", were fixed with two types of adhesive mortars, one commercial and the other produced in the laboratory (here referred to as "PM" mortar). Average TBS adhesion values were higher for the rougher plates, as expected, since in this condition there is a larger exposed surface of the minerals, resulting in a greater number of electrochemical charges available to interact with the adhesive mortars. In quantitative terms, the results indicate average values of 1.39 MPa and 1.16 MPa, respectively, for the higher and lower roughness of specimens fixed with Commercial mortar. Regarding the adhesion for PM mortar, values obtained in specimens with smooth, moderately rough and rough surfaces, respectively, were, on average TBS of 2.06 MPa, 1.42 MPa and 1.47 MPa, values higher than for the CM mortar. Importantly, in these last two test conditions, all failures occurred in the stone, indicating that the PM mortar adhered very well to rougher surfaces, i.e., the stone and the standard substrate. So, it is plausible to consider that TBS values of the PM Mortar should be, in practical terms, higher than measured in the tests, since they reflected more conditions of the rock than the mortar. Such information indicates that detailed evaluation of the types of failure in the adhesion tests was important to corroborate the better TBS results for the mortar prepared in the laboratory with CPV-ARI cement.