The paper outlines the manufacturing characteristics and the experimental methodology used to study modified and unmodified spruce and ash wood under axial compression along the fibres, particularly in acidic environments. Histograms illustrating the dynamic changes in key strength and deformability parameters of modified and unmodified wood during exposure to an acidic medium were constructed. The study established that wood modification using the polymer composition “Silor” significantly enhances the mechanical properties of the tested wood species when exposed to aggressive acidic environments. Specifically, the ultimate compressive strength increases by 1.46–1.65 compared to unmodified specimens immersed in lactic acid and by 1.38–1.43 times in hydrochloric acid. The relative critical strain decreases by 1.08–1.15 times in lactic acid and by 1.08 times in hydrochloric acid. The relative residual strain reduces by 1.07–1.19 times in lactic acid and by 1.04–1.09 times in hydrochloric acid. The modulus of elasticity increases by 1.26–1.37 times in lactic acid and by 1.21–1.35 times in hydrochloric acid. Comparisons were made based on a 28-day immersion of modified and unmodified wood in the acidic solutions.