Factors Influencing Adhesive Bonding Efficiency in ETICS Application

In this study, physical factors influencing the efficiency of adhesive bonding in External Thermal Insulation Composite Systems (ETICS) using the ribbon-and-dab bonding method were analyzed. Tests were carried out to show the distribution of pressure transmitted through thermal insulation to adhesive mortar and substrate during bonding, and to demonstrate the relationship between pressure, adhesive layer thickness, and bond strength of mortar to concrete substrate. The analysis was also based on in situ observations, laboratory experiments, and numerical modeling, with particular attention paid to contact pressure and adhesive strength depending on cement-based mortar layer thickness. Example pull-off tests (CAST, DAST) performed on dabs showed that increasing thickness from 10 mm to 20 mm caused a decrease in bond strength in the central area by about 86% for tested adhesive mortars and substrate—values dropped from 1.8 MPa to below 0.25 MPa, while edge zones often showed no adhesion. Pressure-mapping tests (PMAST) revealed distinct pressure zones within dabs and perimeter ribbons. The analysis showed that average normalized pressures in adhesive dabs reached about 52% of the maximum value, while the [0.9; 1.0] pressure interval covered about 12% of the contact area. Based on empirical data, a decay function was developed to build a model of radial pressure attenuation. Monte Carlo simulations defined ranges of random model parameters and variability of average pressures in a 10 mm adhesive dab. The model allowed inclusion of a peripheral zero-pressure ring and enabled simulation for a 20 mm layer, confirming that increased thickness led to reduced contact pressure and explained the decrease in bonding performance.