Liquid water absorption of wood surfaces with and without coating, before and after exposure to artificial and natural weathering has been studied. Spruce, oak and sapele samples have been exposed to the cycle of EN 927-6, to the cycle of the Gardner wheel and to natural weathering. Five coatings were tested including solventborne and waterborne, semi-transparent and opaque products. Exposure to weathering led to a significant increase in water absorption of uncoated wood with the biggest increase for oak. For coated surfaces the influence of the weathering depends on the coating type. The exposure improves the water barrier properties of pigmented products whereas it reduces those of semi-transparent coatings. The combination of water absorption measurement and weathering gives more information about long-term performance of coatings than a single measurement of water uptake on fresh and unweathered coated wood. The water absorption is better correlated with the spreading rate than with the film thickness. From water uptakes of coated and uncoated surfaces the water protection efficiency has been calculated. This parameter offers the advantage to work with permeability classes rather than with a limit of absorption as specified in EN 927-2 and which is valid for spruce only.

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