Water Repellents Reduce Rain-Caused Paint Blistering on Wood Siding

Rainwater is an important, though not generally recognized, cause of paint difficulties in wood-sided houses. It gains entry back of the siding chiefly by capillary action, working through the lap joint between courses of bevel siding. High winds are a minor cause. Laboratory tests have shown that entry of rainwater through house siding can be minimized or eliminated by dressing the back of standard-pattern siding so that a tight joint, which can be more or less sealed with paint, is formed between the courses, modifying the standard pattern by dressing the back side and adding a horizontal groove; treating conventional or modified siding with water repellent before it is nailed to the house; and applying a water repellent to the siding of a completed house before the house is repainted. Siding dip-treated with repellent provided the best resistance to the capillary action and indications were that back dressing in conjunction with dip-treating would offer even better resistance. Water entry through end joints was not evaluated.

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