How silane modification affects the properties of gap fillers based on a mixture of wood powder and glass microballoons intended for wooden artefacts exposed outdoors

Gap fillers intended to fill gaps and holes in wooden artefacts exposed outdoors should have specific properties to efficiently serve their purpose, including compatibility with wood in terms of mechanical and moisture behaviour, resistance to external conditions, good adhesion to the wood surface, and ease of preparation and application. This research focuses on gap fillers composed of a mixture of wood powder and glass microballoons, using various adhesives, and investigates the effect of silane modification (Methyltrimethoxysilane and (3-Glycidyloxypropyl)trimethoxysilane) on their selected properties that include dimensional stability when exposed to moisture and liquid water, thermal stability, mechanical properties as well as features vital from the conservation perspective, such as workability of wet filling masses during preparation and application, their shrinkage during drying, and easiness of finishing their surfaces to adjust their appearance to the surrounding wood. The results show that silanes can reduce water uptake by the prepared composites, limit the wettability of their surfaces, and shrinkage during drying, while also improving the thermal stability of most of the composites without impairing other essential properties, such as mechanical behaviour, workability and finishing. However, their effect is not the same for all filling masses. The best performance was observed for gap fillers with Paraloid B-72 as an adhesive. Overall, prepared composites show potential for filling gaps in wooden artefacts exposed outdoors and benefit from modification with silanes. However, due to the complexity of the applied components and their interactions, the effects of silanes on such composites remain difficult to predict, highlighting the need for further research to confirm their usefulness in conservation practice.