Test method
ASTM G21 fungal resistance testing
ASTM G21 determines the resistance of synthetic polymeric materials to fungi. Specimens are inoculated with a mixed fungal suspension and incubated under conditions that favour growth; the growth that appears on the specimen is then rated on the standard's scale, from none through to heavy.
- Result
- A growth ratingFrom none through to heavy, not a count
- Organisms
- A mixed fungal suspensionAn antibacterial claim is a separate test
- For
- Synthetic polymeric materialsMould and mildew on plastics and building materials
- May also need
- ASTM G29For a material that will sit outdoors
- Turnaround
- 14–30 daysDate confirmed before you ship
The test in four steps
Drawn as a schematic, not photographed at our bench. The drawings show the sequence; the conditions are the standard's.
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Treated and control
The treated material and, where possible, the same material untreated as a control.
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Inoculate with fungi
The specimens are inoculated with a mixed fungal suspension.
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Incubate
They are incubated under conditions that favour growth.
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Rate the growth
Growth on the specimen is rated on the standard's scale, from none through to heavy.
Solid green outline: treated. Dashed gray outline: untreated control. Green dots: the organisms.
What the test involves
It is the method to ask for when the concern is mould and mildew on a plastic or a building material rather than bacteria on a fabric — humid warehousing, tropical installation, outdoor exposure, or a buyer's durability specification.
Because the result is a rating rather than a count, it answers "does this material support fungal growth" rather than "by how much does it reduce it". If your claim needs a number, the antibacterial methods are the ones that produce one.
We run ASTM G21 in our BSL-2 laboratory in Bandung, certified annually by the International Antimicrobial Council (USA) and participating in AATCC's PTP4 antibacterial proficiency program.
What you receive
- An independent test report in IAC or AATCC format
- The rating or observation the standard defines, against the untreated control
- A certificate your customers, auditors, and procurement teams can verify
Common questions
Is this the right test for mould on a building material?
Usually yes, for a synthetic polymeric material. Tell us the substrate and where the product is installed — a material that will sit outdoors may also need ASTM G29 for algal resistance.
Does a good ASTM G21 result mean my product is antibacterial?
No. Fungi and bacteria are different organisms and the methods do not substitute for each other. If you need to make an antibacterial claim as well, that is a separate test — see ASTM E3160 or AATCC 100.
What samples do I send?
The treated material and, where possible, the same material untreated as a control. We'll confirm sizes and quantities when you book.
How long does it take?
14–30 days, depending on the method and the current queue in the lab. We confirm the date when we accept the sample, before you ship anything.
Related methods
Not sure which one your buyer wants? Send us the specification and we will read it with you before any sample ships.
Book an ASTM G21 test
Tell us the material and where it will be installed. We'll confirm the method and what the report will contain.