Structural Bonding of CCA-Treated Wood for Foundation Systems

An effective adhesive bonding system for wood foundations will eliminate the need for costly corrosion-resistant fasteners, provide stronger foundations, and allow more efficient structural design with wood. Chemical surface treatments to improve bond integrity of a gap-filling phenol-resorcinol adhesive on unplaned CCA-treated plywood and lumber were tested. The treatments consisted of aqueous solutions of sodium hydroxide, sodium carbonate, and tri-sodium phosphate, in 1 Normal and 3 Normal concentrations, applied by brush to plywood and lumber bonding surfaces. The time of during between brushing on of chemical solution and applying adhesive was considered. The effect of alkali on bonds was tested by boiling specimens in water and exposing specimens to prolonged high moisture conditions. The effects of all treatment combinations were evaluated in terms of shear strength and wood failure in both dry and wet conditions, as well as resistance to lamination. The sodium hydroxide brush treatment, at the 3 Normal concentration (120 g/L), made a dramatic improvement in bond strength and durability. The alkali could be brushed on anywhere from a few minutes to 24 hours beforehand, although best results were achieved after 1 hour of drying. Continuous boiling of specimens up to 600 hours indicated the sodium hydroxide treatment did not cause an unusual rate of bond deterioration. This adhesive-bonding technique will be tested in full-size shear walls under racking loads.

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