Salt Damage in Wood: Controlled Laboratory Exposures and Mechanical Property Measurements

Abstract

Salt damage in wood can be recognized by its stringy appearance and is frequently observed in wood used in maritime structures and buildings built near the ocean. Whereas salt-damaged wood is common, little is known about the mechanism by which salt water alters the wood structure. There is no information on the effects of salt damage on the mechanical properties of wood. In this study, a laboratory method for creating salt damage in other porous materials was applied to wood. Wood pillars were placed in a reservoir of 5 M NaCl and exposed to a 40% RH environment. Capillary action pulled the salt water to the upper part of the pillars which were dry. Large deposits of effloresced salts were observed. The changes in mechanical properties caused by the salt were measured by the high-energy multiple impact (HEMI) test. Salt damage caused a reduction in the resistance to impact milling (RIM) of 6.5%, and it was concluded that salt damage causes only minor effects on the strength of wood. The tests were not conclusive as the exact mechanism of salt damage in treated wood. However, diffusion of mineral ions through the cell wall was found to be a key step in the salt damage mechanism.