Violin varnishes are known to affect both moisture absorption and vibrational properties of violin wood. However, traditional multi-layered varnish systems suffer from substantial wear as a result of intensive use, which calls for deeper understanding of the specific impact of individual layers. Using sophisticated in-situ neutron imaging and vibrational modal analysis, we show how wood sorption and vibrational behavior of tonewood depend on the build-up of the varnish system. The results demonstrate the protective effect of complete coatings and emphasize that strongly worn regions cannot accomplish the function as an effective moisture barrier, which might pose a risk for frequently played or aged string instruments. Furthermore, the build-up of the varnish system affects the vibrational properties of the tonewood, influencing its final sound quality. This delicate interplay should be considered both for the handling of antique and aged violins and for the production of modern high-quality instruments.