New Standards on the Shelf
Wood and Composite Stains Debut
by Ken Brenden

As we approach the rough weather season, the exterior durability of the finishes on homes and light commercial buildings is a concern to those in the door and window industry.

Certainly these and allied concerns have long occupied the thoughts of the American Architectural Manufacturers Association (AAMA) coatings and finishes committees and task groups. The result has been a growing library of performance standards for organic coatings on various substrates, all designed to deliver increasing durability under outdoor exposure.

On the shelves are the series governing organic coatings for aluminum (AAMA 2603/2604/2605), organic coatings for thermoplastic profiles such as PVC and cellular PVC (AAMA 613/614/615) and organic coatings for thermoset profiles such as fiberglass (AAMA 623/624/625).

Now joining them on that shelf is the first of a developing series governing exterior stains (as opposed to opaque paints) for wood and composite products. The first among these, AAMA 633, has just been released. Officially titled Voluntary Specification, Performance Requirements and Test Procedures for Exterior Stain Finishes on Wood, Cellulosic Composites and Fiber Reinforced Thermoset Window and Door Components, AAMA 633 spells out test procedures and performance requirements in terms of film integrity, exterior durability and general appearance over a period of several years.

To conform to AAMA 633, a minimum of 30 stained 2- by 6-inch samples—representative of the wood, cellulosic composite or fiber reinforced thermoset substrate for which they are destined—are tested for nine essential properties:

Color uniformity: This is based on visual inspection under a uniform light source, according to applicator or end-user visual standards.

Specular gloss: This is intended to meet end user’s specified range of values when measured per ASTM D523.

Film adhesion: There can be no film removal, per the ASTM D3359 tape pull-off test, for both dry adhesion and wet adhesion (after 24 hours immersion in warm water). Additionally, there can be no blistering, haze or change of color beyond seven ?E
Hunter units.

Direct impact: No removal of film per the tape pull-off test after impacts driven by increasing loads (up to 60 inch-pounds or
until brittle failure of the substrate, whichever occurs first).

Chemical resistance: Samples cannot exhibit blistering or hazing or a numerical color difference greater than seven ?E Hunter units after 15-minutes exposure to a 10 percent solution of muriatic acid; after 24-hours of exposure to mortar at 95 percent or higher humidity and 100°F, or after 24 hours immersion in a 1 percent solution of detergent.

Humidity resistance: No blistering or hazing or a numerical color difference any greater than seven ?E Hunter units after 1,000 hours exposure at 100°F and 95 percent relative humidity.

Cold crack cycle: There can be no cracking, loss of adhesion or blistering; and no cloudiness or haze, or a numerical color difference any greater than seven ?E after 15 test cycles, each consisting of 24 hours exposure at 100°F and at least 95 percent humidity followed immediately by 20 hours exposure –10°F and then four hours at room temperature.

Oven-aging: There can be no loss of adhesion per the tape pull-off test after seven days exposure to 140°F followed by 96 hours exposure to 95 percent humidity.

Weather exposure: There can be no checking or crazing, no loss of adhesion after the tape pull-off test, no color difference greater than seven ?E units and no conspicuous chalking after a minimum of one year of outdoor weathering exposure at any of the three test sites: Florida (tropical), Arizona (desert) and a northern temperate site experiencing freeze/thaw conditions.
New colors can skip the weathering test if they are based (within certain limits) on a previously-tested formulation.
T
hese are not trivial tests, and it has taken some time to regulate the basic ASTM methods to yield optimally-meaningful results for the coatings and substrates involved.

Ken Brenden serves as technical services manager for the American Architectural Manufacturers Association in Schaumburg, Ill.

DWM
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