A New Device for Studying the Blister Resistance of House Paints

A new paint blister box that simulates cold-weather condensation and rain penetration in house siding has been developed. The new apparatus consists of a test chamber 33 inches wide, 42 inches high, and 84 inches long, on top of which is a penthouse of like width, 31 inches high and 41 inches long. The box is covered with exterior grade Douglas- fir plywood. This box makes it possible to study the resistance of paints to moisture blistering under conditions that resemble closely the actual conditions that may occur on houses. It permits study of blistering with water supplied entirely by simulated rain on the painted faces of the test panels. Therefore it is useful in evaluating treatments of siding, such as water-repellent preservatives, that may be effective against outside water but not against cold-weather condensation or vapor from within the structure. The milder conditions of cold-weather condensation used in the blister box are helpful for the closer comparison of paints that blister but vary in their sensitivity. Nevertheless, the most striking differences are those between paints that are highly resistant and paints that are sensitive to moisture blistering.

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