The article presents the influence of the type of substrate and its treatment on the pull-off strength of gypsum plaster. Most of the papers describe the effect of recommended surface treatment. The main target of this study is to show that different approaches of preparing primer have an impact on the properties of gypsum plaster. For the purpose of the article, three different types of concrete substrate were analyzed: aerated, light-weight and ordinary. Samples of the surfaces were treated by applying primer or diluted primer. To compare strength results, one of the substrate surfaces was prepared without the primer. Pull-off strength tests were performed for all the samples. As a result of this study, it has been proved that the optimal substrate surface for gypsum plaster is light-weight concrete. Moreover, it was found that applying primer negatively affects the pull-off strength of gypsum plaster. Using the primer, the gypsum plaster dry-off process is disturbed. This new discovery can be helpful to understand the primer impact on the pull-off strength of the gypsum plaster, and it shows that the primer composition needs to be analyzed and there should be taken actions to improve it properties.