**4. Discussion**

For the steel and aluminium components, no metal came off the adhesive in any of the measurements; the destruction always occurred in the underlying plaster. In the case of the copper alloy, a difference was determined between the tensile and shear tests. While in the tensile test the adhesive was torn off the plaster in all cases, in the shear test, on the other hand, all the measurements showed a complete peeling of the adhesive from the copper surface, and only in one case did a partial peeling of the adhesive from the copper surface combined with destruction in the plaster occur, as can be seen in Figure 5. The declared strength of the plaster by the manufacturer was 0.3 MPa. The real values of the observed tensile and shear adhesive strengths essentially exceed this value two-fold, which was clearly due to the higher strength of the plaster and its inherent adhesion to the underlying screed. In terms of the measured data, there was no significant difference in

whether the destruction occurred in the surface thin-layer plaster or the screed, and the values of the measured forces and the calculated stresses were similar. However, lower values were obtained in the case of copper in the shear test, where the destruction occurred almost exclusively by peeling off the copper strip.

In addition to the tests of the bonded joint between the metal element and the plaster substrate, the tensile and shear properties of the adhesive itself were measured. The measurements were carried out using a standard tensile and shear test, where the aluminium targets and strips were bonded together, and subsequent destruction in the adhesive itself occurred during the measurement. Copper and steel zinc-plated elements were not used to measure the adhesive parameters. As expected, the adhesive itself performed better in both tests in terms of both adhesion and elongation (see Figure 5). In terms of tensile adhesion, the adhesive performed better by 34% on average, and in terms of shear adhesion, it performed better by 25%. In the case of elongation, the adhesive parameters were on average 150% better in the tensile test and 89% better in the shear test. However, elongation is not as important as adhesion in the case of bonding sheet-metal components to a facade. In this respect, the results demonstrated the fundamental fact that, under standard laboratory conditions, the tensile- and shear-load capacities of the adhesive itself were not significantly better than those of the bonded joint, which involved a metal element bonded to the surface of the used multi-layer facade plaster. It should be noted that the research did not include other important factors such as the effect of freezing and thawing, the effect of moisture, sudden temperature changes as described by Franco and Royer-Carfagni [14], adhesive thickness or ageing of the multi-layer plaster [15–19]. In practice, it would be glued to facades already subjected to external environmental influences, as described by Bochen [20].
