Standard principles for applying the so-called Scotch tape test for assessing the surface cohesion characteristics of materials were explained in an earlier paper on testing stone consolidation effects (Drdacký et al., Mater Struct 45(4):505–520, 2012). The method has also been used for evaluating the strengthening of surface mortar layers, though it is not supported by any standard or reliably verified recommendations for its application. As in the case of stone testing, its applicability can be overestimated, and arbitrary use of the test without adequate knowledge and sufficient understanding can lead to results and assessments that are not intercomparable or reproducible, and which are also in many cases incorrect and severely biased. This paper reports on the results of a recent study aimed at establishing limits for the application, reliable procedures, and a “standard” protocol for testing the cohesion characteristics of brittle and quasi-brittle materials, mainly mortars. This paper discusses the effects of various surface qualities of mortar or rendering, and suggests recommendations for performing peeling tests on mortar surfaces. It presents a mathematical procedure suitable for evaluating the results. Again the recommendation is to perform repeated peeling on an identical place on a surface in order to eliminate the effect of the natural decrease in the material detached from the subsurface layers, which might be incorrectly interpreted as a consolidation effect. The examples and the validation measurements presented here include laboratory measurements.