Treatments to Improve the Dimensional Stability of White Spruce Cladding

Changes in wood moisture content below the fiber saturation point result in dimensional changes. This creates stresses in the wood which may manifest as checks and cracks. These impact the appearance of wood products and limit the use of wood in some applications. Many chemical treatments to improve wood stability have been developed, though they are generally only applied to wood species with high permeability. The present work investigates several commercial-scale and lab-scale modification treatments for their ability to stabilize white spruce, a refractory softwood. Modified white spruce was evaluated for weight percent gain after treatment, dimensional stability in humidity and immersion, total color change after accelerated UV exposure, and coating adhesion before and after UV exposure. All treatments improved stability with anti-swelling efficiency between 11 and 59%. However, these treatments were also associated with increased color change after accelerated UV exposure and poorer adhesion of a water-based stain. The improvements in dimensional stability were generally lower than those reported for permeable species, and it’s unclear if they would meet end-user expectations. Additional research is needed to further enhance performance and to overcome the resulting photostability and coating adhesion challenges.