The exposure to chemically-aggressive media causes a structural modification of wooden members. The related mechanisms are called wood corrosion. The subject of the studies was an approximately 100 year’s old warehouse, which was executed as HETZER-construction and has been used as storage for potassium salt. The assessment of the degree of modification and the evaluation of the strength reduction was the aim of the studies. Test on the strength as well as chemical analyses have been carried out. The results showed a clearly visible modification of the examined material due to the exposure to the salts. This was recognizable by the superficial macroscopic modifications as well as by a reduction in the strength of the material in the periphery of the cross-section.