Oriented strandboard (OSB) and plywood was exposed to treatments of no protection, nonfilm-building coating (lasur), and film-building (painted) protection to Study their physical and mechanical performance when subjected to 40 degrees C and 95 percent relative humidity in an air-conditioned chamber for a total period of 800 hours. Evaluations were made at 100, 200, 400, and 800 hours under these conditions. Board samples were directly exposed to treatments in the size established by European standards for the physical and mechanical properties evaluated to determine variations in moisture absorption, thickness swelling, and bending strength. Results indicated fluctuations in the evaluated properties as well as increases and losses of weight and mechanical resistance, although these values were within the ranges determined by the quality standards. But, the useful life of the boards was lessened and shortened affecting its competitiveness against alternative materials.