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Architectural Coatings
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 November 2006
Feature
 
Neal Rogers has served as chair of Subcommittee D01.42 on Architectural Coatings for two years. He holds a B.S. in chemical engineering from the University of Illinois and an M.B.A. from the University of Southern California. Rogers has 10 years’ experience in the coatings industry as a chemist and laboratory manager. He works for Cook Composites and Polymers.

Architectural Coatings

Measuring Paint Performance

Architectural coatings are the paints and finishes you find on the inner and outer surfaces of residential and commercial buildings. These finishes cover a vast category of products — everything from wall paints to typical semi-transparent deck stains and even some floor paints.

While serving a practical and protective purpose, many architectural coatings are decorative in nature, whether changing the color of an interior room or freshening up the exterior appearance of a house. They may be clear or opaque, flat or glossy, white or of various colors. Regardless of the appearance, all architectural coatings require some level of functional performance. For instance:

• Can you wash off marker stains left behind by your two-year-old budding artist?
• How many coats does it take for a “one-coat” paint to hide the previous color?
• Is the clear finish on your deck blocking water from penetrating into the deck boards?

The 34 active ASTM standards maintained by Subcommittee D01.42 on Architectural Coatings address these questions and more. These standards are used by paint manufacturers and raw material suppliers to help achieve consistent and repeatable practices for the evaluation of products used by both consumers and professional painters. The architectural coatings subcommittee is currently working on several standards development projects that are highlighted in the following sections.

Low Temperature Application
One active work area within D01.42 is the development of standards that demonstrate how low temperature application affects the quality of a paint film. Some paints are designed to be applied in an environment where the air temperature is 40 °F (4 °C) or even colder. In seasonal climates, the number of available days to paint outside is limited because of rainy and cold days, so the occasional need to apply paints at low temperature is especially important to painting contractors. A formulator who is developing a paint for low temperature application needs to be certain the paint will form a sound film in a cold environment. If a product does not achieve good low temperature film-formation, it may lose gloss or even crack when applied if the surrounding temperature is too low.

Further, a good paint must have the capacity to be touched up or repaired without its overall appearance being affected. Touch-up characteristics are especially important for painters who work on new construction, where touch-ups are typically completed on a different day than the main application of paint. If heating systems are not yet operational, the temperature of the interior walls of a house will fluctuate with the outside temperature. Thus, especially during winter months, it is questionable whether a painter will experience the same environmental conditions when it is time to touch up the original paint.
A paint applied originally at a warm temperature, when applied under colder conditions, may not achieve an identical color or gloss. Subcommittee D01.42 has proposed a standard practice for laboratories to evaluate paint application and touch-up under constant or varying environmental conditions. By following this standard practice, a manufacturer can be confident that paints are performing well under all potential usage environments, whether warm or cold, humid or dry.

Open Time
A second area of work for D01.42 is measuring the open time, also known as “wet edge” or working time, of a paint sample. Many people know painters who turn their noses up at water-based paints and insist that oil-based paints are the only paints they will use because of superior performance. In actuality, premium quality water-based latex paints have matched or surpassed the performance of oil-based paints in practically all film durability performance measures. Painters do have one legitimate argument supporting the benefit of oil-based paints over water-based latex systems: the oil-based paints they have used for years maintain a wet edge much longer than the water-based paints. If a painter is working on a wall or door frame, he can come back after 15 or 20 minutes and repair any drips, sags, or other marks in the wet paint so that the finish still looks uniform. Any marks left by the brush will still flow into the surrounding painted areas. With typical water-based paints, a painter may only have 5-10 minutes before the wet paint starts to “close.” In this case, brushing back into the paint after it passes its open time yields distinct brush marks where the attempt was made to repair the finish.

The proposed standard test method for evaluating the wet edge of latex paints involves casting a uniform film of the paint and then making a series of marks in the paint immediately. Over a progression of timed intervals while the paint dries, the operator brushes into the finish and evaluates how effective the brushing was at removing or repairing the initial mark that was made. This standard is currently being evaluated in an interlaboratory study. If there are no unexpected findings, the method is planned for ballot submission in 2007.

Water Repellency
The effectiveness of wood waterproofing coatings is another area of focus for D01.42. The wood coatings task group is working on an enhancement to ASTM D 4446, Test Method for Anti-Swelling Effectiveness of Water-Repellent Formulations and Differential Swelling of Untreated Wood When Exposed to Liquid Water Environments. This title is quite a mouthful and is commonly referred to in the industry as the “swellometer” test. The test method uses a specially designed instrument, known as the swellometer, to measure the water uptake of a narrow wood wafer that is cut in a special orientation. Instead of measuring the weight of water absorbed by the coated wood, the swellometer device measures the tangential expansion, or swelling, of the coated wood wafer.

The swellometer methodology for measuring water repellency was documented in a federal specification test that dates at least back to the 1950s. At the time the method was created, there was wood readily available that met the required specification of straight-grained, flat sawn lumber with 10 inches [250 mm] in the tangential dimension. However, modern forestry techniques yield lumber where the entire 10-inch [250 mm] board length is not straight-grained. In new-growth pine forests, trees grow more quickly and are harvested early relative to the old-growth lumber sourced for the original test. As such, a testing laboratory that wanted to run this method would have a difficult time finding the required lumber. ASTM D 4446 is being re-qualified to enable either a 5-inch [125 mm] or 10-inch [250 mm] wood wafer length to be used in the test. In order to adopt this change, a new interlaboratory study has been initiated to look at the differences achieved between 5-inch [125 mm] and 10-inch [250 mm] wafers. The method will be updated accordingly once the results are reviewed in 2007.

Stainblocking Coatings
An area of future interest to Subcommittee D01.42 is to expand the standard methods used to evaluate the stainblocking characteristics of coatings. There is already one method in this area, D 6686, Test Method for Evaluation of Tannin Stain Resistance of Coatings. This method is used to measure the capacity of a paint or primer to seal tannins and extractives that come from within a piece of wood. The method is well-suited to coatings that are used directly over uncoated wood. However, other coatings, stainblocking primers for instance, need to be able to block stains from water damage, smoke exposure, or household items such as markers and ink pens. For a primer, stainblocking performance is critical to ensure that stains will not bleed into the finished topcoat.

Closing Comments
One can imagine from this article that there is much more to measuring paint performance than simply counting the minutes it takes paint to dry or making sure it sticks to the wall. Low temperature application, open time, water repellency, and stainblocking are just a few of the performance attributes that demonstrate the breadth of architectural coatings performance measures. //

 
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