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
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
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
New colors can skip the weathering test if they are based (within certain
limits) on a previously-tested formulation.
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.
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