Mold & Mildew Resistance and Firestop Systems

Standard formulating procedures for sealants, coatings, and other building materials consider mold resistance. Mildewcides and fungicides protect against mold and fungal growth in both wet and dry stages. Testing is conducted to various ASTM standards to evaluate mold resistance.

Testing for Mold Resistance:

Polymeric materials such as sealants, coatings, or plastics are tested according to ASTM G21, “Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi”. After the 28-day exposure period (27°C ± 2°C; 85% R.H.), the samples are evaluated for fungal growth and rated to the following scale where ratings of 0 or 1 indicate mold resistant:

Observed Growth on Specimens
None 0
Traces of Growth (<10%) 1
Light Growth (10-30% 2
Medium Growth (30-60%) 3
Heavy Growth (60% to complete coverage) 4


Interior coatings, including gypsum board products, are tested according to ASTM D3273, “Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber”. Samples are hung in an environmental chamber containing soil seeded with fungal spores for 28 days (32.5 ± 1°C and 95 ± 3% R.H.) and examined for fungal growth and defacement. The rating is based on visual defacement of fungal growth on a scale of 1-10 with 10 being the best rating (i.e., zero defacement). Moisture resistant gypsum board typically achieves a rating of 8 to 9.

The following list of STI products are classified as mold resistant per the applicable standards.

Product ASTM G21 Rating ASTM D3273 Rating
AS 0
ES 0
LC 0
WF 0
SIL300 and 300SL 0
Fast Tack 0
Cable Spray 0
SSP Putty and Putty Pads 0
SNS Sealant and Spray 0
Safing Spray 0
SSW Wrap Strips 0
TTG* 10
*A product like TTG (i.e., a gasket) should be tested to ASTM D3273 like the gypsum board.


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