Mold Measurement, DWM 2004

August 2004

Mold Measurement
WDMA Considering Test Method for Resistance to Mold
by Dan McLeister

Late last year the Window and Door Manufacturers Association (WDMA) launched a long and complicated process that will continue throughout this year to examine test methods for mold growth resistance on windows.
The task is complex because there is not one system that will work for all types of windows—hardwoods and softwoods, according to Andersen Corp.’s Bruce Bohnen, chairperson of the WDMA treatments and coatings committee. At a recent WDMA meeting, a task group, chaired by Alan Ross of Kop-Coat Inc., was established by Bohnen’s committee to complete further research on the mold and mildew growth issue.

Mold Differences Abound
There has been no universal test because, not only are the basic materials different, but the mold or mildew organism is also different for each substrate.

“Right now, we are in the beginning of a search for test methods. But I believe the problem is solvable. The test methods and fundamental science behind them are out there,” said Bohnen.

For mold to develop, three ingredients are necessary: mold spores, which exist just about everywhere in the outdoor and indoor environment; a food source for the mold, which can be any organic material, including wood, paper, adhesives, caulk, and many other construction materials; and the right environment, namely temperature and moisture.

“Remove or control any one of these, and mold cannot grow,” said Jeff Lowinski, WDMA’s vice president, technical marketing.

“Window and door manufacturers are working to control the food source and moisture environment through the use of innovative materials, treatments and exterior coatings,” he said.

The mold issue is complicated and involves other products, such as siding, as well as installation techniques. No one product or application controls the whole process from which mold might develop. But a method to test for the resistance to mold growth on windows is an important part of the whole process, according to Bohnen.
“If a reliable test is proven, that means we can start sorting out the issues,” he said.

The mold issue is also complicated because there are several different strains of mold and the type of mold growth would need to be identified. Most varieties are harmless to all but the most sensitive individuals are those who suffer from allergic reactions, compromised immune systems or asthma. A particular bad strain and the one that has gotten most of the media attention is the stachbotrys-atta. There is still a great deal of controversy over the health issues related to mold. Mold has been around since the beginning of time and the scientific evidence of its adverse health effects have been debated by the experts.

Test Method Options
One option is for WDMA to reference a test method being considered by the American Wood-Preservers’ Association (AWPA)-Standard Method for Determining Preservative Fixation of Waterborne Wood Preservatives. The method was submitted by Paul Morris of Forintek, a company located in Vancouver, British Columbia, and it could be adopted as an AWPA standard. AWPA addressed this proposed standard at its meeting on May 17 and it hopes to finalize the standard at its meeting in September. The next step would be a ballot of AWPA members which could take place before the end of this year, according to Darrel Nicholas, chairperson of the AWPA Subcommittee P-6, Methods of Evaluation of Wood Preservatives. However, Nicholas said there could be problems because of new wood preservatives being used.

Forintek and the wood industry had experienced increases in inquiries regarding mold and the suitability of wood as a substrate for its growth. One of the company’s projects included development of a lab test method for mold resistance since the company believes that moisture management is a key to addressing indoor air quality health issues and also to minimize mold growth. The primary cause of mold, Morris said, is often associated with water, building system failures (envelop and ventilation) and occupant contributions (lifestyle and maintenance).

The Forintek test was developed initially when the company started work in 1996 with the Alberta Research Council developing OSB with improved mold resistance. The method is an adoption of an existing ASTM standard for treating paints.

The test chamber is a polypropylene tank covered with a pitched roof to allow condensation to run back to the bottom of the chamber. Three inches of water on the bottom of the chamber and a tray with a moistened soil provide humidity and natural spore inoculum for the system.

Constant spore distribution is assisted by an air-circulation fan. The temperature and humidity are controlled electronically to be constantly favorable to mold growth. Test samples hang over the unsterilized soil and are challenged additionally by spraying them with a mixture of mold spores. Samples are removed, weighed and rated for the extent of mold growth every two weeks for the eight-week duration of the test. The company has now done 24 tests for 13 clients using this test method.

ASTM does have a test method intended for the accelerated evaluation of an interior coatings’ resistance to fungi defacement. But the organization said use of this test method for evaluating exterior coatings’ performance has not been validated, nor have the limitations for such use been determined. The ASTM test method describes a small environmental chamber and the conditions of operation to evaluate, reproducibly in a four-week period, the relative resistance of paint films to surface mold fungi and mildew growth in a severe interior environment.
The biggest reaction to the ever-increasing publicity to the mold issue is the growth of the “green building” movement and environmental certification programs. Architects, builders, remodelers and manufacturers are jumping on the bandwagon, touting the potential benefits to the environment and the health of the homeowners, with improvements in energy efficiency and indoor air quality. WDMA has formed an environmental standards task group to monitor these programs to keep their members informed on the latest developments.

It’s apparent, said WDMA’s Bohnen, that companies are just starting to realize how complicated the mold problem is. And, he added, there is more to consider than just the test methods for resistance to growth of mold.