Key takeaways
- ASTM D3273 is a test method used to evaluate the resistance of interior coatings to mold growth under highly humid chamber conditions
- ISO 22196 is a test method used to quantitatively evaluate the antibacterial activity of non-porous plastics and treated surfaces.
- ASTM D3273 focuses on fungal resistance while ISO 22196 focuses on the bacterial reduction
- Results for report differently for both test methods : Visual mold rating (ASTM D3273) vs Log reduction R value (ISO 22196)
- Selecting the right test depends on the type of material, target microorganism and intended product claims.
Summary
ASTM D3273 test evaluates the resistance of interior coatings to mold growth under high humidity conditions. The results are represented as a visual rating system. ISO 22196 is a test method that evaluates the antibacterial activity on plastics by assessing the bacterial reduction after 24 hours. Manufacturers choose ASTM D3273 for mold-resistant coating claims and ISO 22196 for antibacterial plastic product claims.
ASTM D3273 vs ISO 22196: What manufacturers need to know?
Mold and bacteria are not the same problem and the tests for both of them should not be the same either.
If you are a paints, interior coatings or treated plastics manufacturer, choosing the wrong test can weaken your claims. ASTM D3273 and ISO 22196 are used for different purposes. It is important to understand the difference between these two test methods to protect both your product performance and compliance position.
Why Mold and Bacteria Require Different Test Methods
Bacteria and mold (fungi) show different behaviour:
1. Biological difference
Mold grow as a visible colonies and spread through their spores whereas bacteria are microscopic single-celled organisms that multiply rapidly on surfaces. So, mold growth can be evaluated visibly but bacterial growth evaluation needs enumeration techniques to assess the survival after exposure.
2. Growth conditions
Mold thrives in prolonged humidity and poor ventilation whereas bacteria grow on nutrient-containing surfaces under controlled moisture conditions. Testing methods should hence replicate these environments. For mold, a chamber promoting fungal growth for weeks is essential and for the survival of bacteria, a sealed film contact system is required
3. Result analysis
Mold resistance is semi-quantitative or quantitative (visual rating scale). Antibacterial activity is quantitative, expressed as log reduction.
What is ASTM D3273?
ASTM D3273 is a test method that evaluates the resistance of interior coatings to mold growth.
In the test:
- Fungal suspensions are spread over greenhouse soil and allowed to sporulate for two weeks.
- Coated panels are suspended above the soil in a humid chamber and exposed for four weeks.
- After a period of 4 weeks, surfaces are visually evaluated for fungal growth and rated on a scale of 0-10.
- A 10 rating indicates no visible mold growth
ASTM D3273 is applicable to:
- Interior architectural paints
- Coatings for humid environments
- Mold-resistant decorative finishes
What Is ISO 22196?
ISO 22196 is a test method used to evaluate the antibacterial activity on non-porous surfaces such as plastics.
Test procedure:
- The sample surface is inoculated with bacteria and covered with a film to ensure proper contact
- After 24 hours of incubation, remaining bacteria are recovered and counted.
- Results are expressed as log reduction compared to an untreated control.
This method provides quantitative data, making it suitable for substantiating antibacterial claims.
It is applicable to:
- Antibacterial plastics
- Surfaces of consumer electronics
- Components of medical devices
- High-touch polymer surfaces
ISO 22196 Passing Criteria
ISO 22196 reports results as log reduction values compared to an untreated control surface.ISO 22196 itself does not define a universal regulatory pass/fail threshold.
How results are expressed?
The antibacterial activity value (R) is calculated using bacterial counts after 24 hours of incubation.
If R = 1 – 90% reduction
If R = 2 – 99% reduction
If R = 3 – 99.9% reduction
If R = 4 – 99.99% reduction
Passing criteria for ASTM D3273
The test method does not specify a โpass/failโ criteria
Results are reported using a scale numbered from 0-10, which reflects the extent of visible mold growth on the surface.
- 10 – No visible fungal defacement
- Decreasing values – Increasing surface coverage by mold
- 0- Heavy or complete fungal coverage
Key Differences Between ASTM D3273 and ISO 22196
| Test standard | Microorganism targeted | Result interpretation | Test principle |
| ASTM D3273 | Mold (fungi) | Visual rating scale (0-10) | Mold growth resistance |
| ISO 22196 | Bacteria | Log reduction (R value) | Antibacterial activity |
Differences between ASTM D 3273 and ISO 22196
Origin of standard
- ASTM D 3273 was developed by ASTM International (American Society for Testing and Materials) and is accepted regionally. ISO 22196 developed by the International Organisation for standardization, is a globally recognised standard. This difference in origin reflects the regional versus global focus of these standards.
Scope of products
- ASTM D3273 provides guidelines for testing of products which include antifungal interior coatings, paint and other surface finishes.
- ISO 22196 standard is for testing antibacterial-treated plastics and other non-porous materials.
Mandatory test strains
- ASTM D 3273 standard – Aureobasidium pullulans, Aspergillus niger, and Penicillium species.
- ISO 22196 standard – Staphylococcus aureus and Escherichia coli are mandatory test strains.
Controlled conditions
ASTM D3273
- Temperature: ~32โ33ยฐC (warm chamber conditions)
- Relative Humidity: Very high, typically โฅ 95% RH
- Exposure Duration: 4 weeks
- Environment type : Constant humidity condensation chamber
ISO 22196
- Temperature: 35ยฐC ยฑ 1ยฐC
- Relative Humidity: โฅ 90% RH (during incubation)
- Contact Duration: 24 hours
- Environment Type: Controlled incubator
Choosing the right test
Manufacturers of interior coatings and antibacterial plastics must consider the type of material and its application before deciding the test method. ASTM D 3273 is developed for testing interior coatings for evaluating mold resistance. ISO 22196 is for testing plastic products that are treated with antibacterial agents to ensure that they are effective in reducing bacterial contamination.
Why Choose MIS for Antibacterial Testing?
At Microbe Investigations Switzerland (MIS), we expertise in providing testing services to make sure your products meet the highest standards of microbial resistance. Be it interior coatings requiring mold resistance testing or antibacterial-treated plastics, our skilled microbiology team is here to help.
Trust MIS for precise and reliable results that will enhance your productโs performance and compliance with international standards.
Contact us today to learn how our specialized services in ASTM D 3273 and ISO 22196 testing can benefit your business.
FAQs
Can ASTM D3273 be used to claim antibacterial properties?
No. It evaluates mold resistance, not bacterial reduction.
Which test should I choose if my product claims antimicrobial?
The choice of test depends on the microorganisms tested for:
- If it is mold resistance – ASTM D3273
- If it is antibacterial reduction – ISO 22196
- If you need broader validation – You can test for both
Is ISO 22196 a suitable test for paints and coatings?
No, ISO 22196 is not applicable for paints and coatings.
How long does each test take?
- ISO 22196 takes 3-5 weeks
- ASTM D3273 takes 5-7 weeks
