Enhancing Functional Properties and Mold Resistance of Gypsum Plasters with Caffeine

Caffeine is a proven bioactive substance against fungi for internal use, without any observed negative effects on properties of wood materials. However, its addition to other building materials for internal use has not yet been tested. For this reason, the effects of caffeine’s addition on selected properties of gypsum plasters were studied. Two experimental approaches were applied in the present study: (A) using an aqueous caffeine solution (20 g/L) for the preparation of gypsum plaster; and (B) immersing the gypsum plaster in the same caffeine concentration. The results showed a significant increase in the compressive strength of the plaster after 7 days of curing in laboratory conditions (variant A—46%, variant B—16%). The application of caffeine led to a substantial improvement in the water resistance of gypsum. Gypsum plasters were also exposed to a mixture of air molds. The plasters directly mixed with caffeine were about 72% less attacked by molds than the control, while immersed samples showed only a 20% reduction in mold coverage. The main conclusions of the study are that caffeine is a suitable additive for the improvement of gypsum’s compressive strength, and its addition leads to a higher resistance of gypsum against humidity and mold attacks.