Thermal and Moisture Gradient Exposure Unit

The construction and use of “Glidden thermal and moisture gradient units” (GTMG units) is discussed. The GTMG units are small enclosures which produce exposures and accelerated weathering results more nearly like actual in-use conditions than do other experimental paint exposure test methods. The effectiveness of this testing method in duplicating paint failure on average homes is pointed out. Failures such as blistering, peeling, mildew, checking, flaking, and dirt collection occur during short exposures. The GTMG units permit early evaluation of coatings under actual conditions of use. The authors conclude that the GTMG units are superior because they permit a normal heat and moisture exposure to the back side of the exposed substrate. The GTMG units are wood-framed structures 12 feet 9 inches long by 5 feet wide and 8 feet 4 inches high. Each long side has 16 openings 36 inches long by 22 inches high which can accommodate test-panel frame assemblies. The structure is roofed in a conventional manner with insulation and vapor barrier. The 36 by 22 inch openings can be used for several different species of siding, for various built-up constructions, or for comparing paints on specimens cut from a single board. Two types of units are described; one is built on cement block footings with a dirt floor, the other is built on a concrete slab and is equipped with a humidifier. Both are gas heated with a thermostat control. Fans supply air circulation to maintain uniform temperature and humidity control. Most paint blistering occurred when the weather was cool; 32 to 45?F, and very humid. After exposure for 3 to 4 hours, blisters form and then disappear when conditions improve. Realistic conditions present in residential housing can be duplicated.

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