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When it comes to mold coatings, follow protocol

September 19, 2010
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In the mold-remediation industry, the most acceptable protocols used to determine mold-resistant coatings performance are the ASTM G-21 and ASTM D- 3273/3274 standards, historically referenced by the coatings industry to demonstrate resistance of polymeric films to mold growth on building materials.

Though different in their protocols, both tests are graded on a rating scale based on performance — designed to provide a greater understanding of the test methods referenced by mold-resistant coatings manufacturers.

ASTM G-21 is the standard practice for determining resistance of synthetic polymeric materials to fungi.

It is a test method that subjects specimens to lab conditions ideal for supporting microbial growth.

  • A chip of the cured sample film is placed directly on nutrient agar in a petri dish; a mixed spore suspension is spread over the test surface, including the sample chip.

The spore suspension is a mixed solution of Aspergillus niger, Penicillium pinophilum, Chaetomium globosum, Gliocladium virens and Aureobasidium pullulans fungi, designed to demonstrate broad-spectrum mold inhibition.

  • After inoculation, the sample is incubated for 28 days at conditions of at least 85 percent relative humidity and at a temperature of 82 to 86 degrees Fahrenheit — conditions ideal for supporting mold growth.
  • At the end of the test period, the samples are rated on a scale of zero to four, with zero indicating no growth on the sample, and four indicating heavy growth (60 percent or more observed growth on specimen).

ASTM D-3273/3274 is the standard test method for resistance to growth of mold on the surface of interior coatings in an environmental chamber.

It is a test designed to simulate a more realistic environment for microbial attack in indoor environments.

  • Coating is applied to sample panels, and then those panels are placed in a controlled environmental chamber for a period of four weeks at 95 to 98 percent relative humidity and 90 to 92 degrees Fahrenheit.
  • Inside the environmental chamber, a layer of nutrient-rich soil and water is placed at the bottom of the unit, and a mold suspension is then used to inoculate the soil.

The mold suspension used is a mixed culture of Aureobasidum pullulans, Aspergillus niger and Penicillium. The mold naturally sporulates and reproduces, growing on any viable surface including the test panels.

  • At the end of the four-week test period, the sample panels are evaluat- ed on a scale of 10 to zero, with 10 indicating no growth, and zero indicating heavy growth.

Tests of this nature should always be performed at independent, certified laboratories, in accordance with published, recognized testing standards; interpretation of the test results should come directly from the testing laboratory.


Scott DeLeo is product manager for Fiberlock Technologies, Inc. (www.fiberlock.com), which produces antimicrobials and coatings for mold remediation.

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