Comparison of Water Resistance for Modified Medium-Density Fiberboard

Commercial medium-density fiberboard (MDF) products, specifically manufactured for water resistance, were evaluated over 8 days under three water exposure regimes: 90 percent relative humidity, one-sided water spray, and one-sided wet pad. A three-cycle wet-pad and drying exposure test was also performed. Rate of swelling, extent of swelling, and irreversible thickness swelling were determined. Acetylated MDF (AMDF) had the best overall performance, followed by steam-injection pressed MDF (SMDF) and polymeric methylene-diphenyl-diisocyanate–bonded moisture-resistant MDF. The fastest rate of thickness swell and linear expansion occurred with exposure to one-sided water spray and the slowest with 90 percent relative humidity exposure. While AMDF was clearly superior after 24-hour exposure, the other MDF products were nearly identical. Significant difference in thickness swell and water absorption between moisture-resistant MDF and SMDF developed after 24 hours. Regardless of the method of water exposure, the trend of best to worst MDF performance was the same.