AbstractIncreased interest in oils and silicones as hydrophobic agents creates the need for testing, with the aim of better understanding their field performance and preparation for an eventual market entrance of these products. This study reveals the aboveground test performance of wood impregnated with epoxidised linseed oil (ELO) and organofunctional alkoxysilanes and compares the achieved results with the significantly more severe inground exposure and initial laboratory tests. Since ELO and siloxanes are not active ingredients, they were combined with fungicides for better performance. Various oil and alkoxysilane retentions and combinations with boric acid, organic fungicides, and creosote were impregnated in wood and tested. Untreated, chromium-copper-arsenate (CCA)-treated and thermally modified samples served as references. Long-term aboveground and inground testing of the studied formulations enforced the conclusion that ELO combined with biocides is suitable protective formulation for timber in both above- and in-ground exposure. Two alkoxysilanes were more effective in timber exposed aboveground. No decay was registered in the ELO and alkoxysilane treated lap-joint samples, while the untreated controls were close to failure after five years of exposure.