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ASTM D3273 Mold Resistance Test for Interior Coatings
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Summary
ASTM D3273 is a recognized test standard that evaluates the resistance of interior coatings and paint films to mold growth under highly humid and warm environmental conditions. The test exposes coated panels to spores of fungi for 4 weeks and gives a rating of mold growth on a visual scale of 0-10, 10 representing the highest mold resistance. ASTM D3273 is widely used for interior paints, coatings, and building materials to support durability claims and ensure product performance in moisture-prone indoor environments.
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Quick understanding about test
ASTM D3273: 2021 – Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber
ASTM D3273 is a standard test used to evaluate the ability of interior coating to withstand fungal colonization and defacement.
Applies to a wide range of products such as building materials (drywall, insulation), coatings (paints, finishes), adhesives, sealants, and more.
- Aspergillus niger (ATCC 6275)
- Penicillium species.
- The environmental chamber is equilibrated at the temperature ~32°C for 24 hours with greenhouse soil and water.
- Green soil is evenly inoculated with fungal suspensions of Aureobasidium pullulans, Aspergillus niger, and Penicillium and left to sporulate for 2 weeks.
- Coated test panels are exposed to the test chamber for a period of 4 weeks and a weekly assessment is done on a 0–10 mold growth scale.
- Validates material performance and therefore minimizes mold-related health risks.
- Proves product reliability and in turn boosting consumer confidence and competitiveness.
It typically takes 3-4 weeks.
After assessing mold growth on panels weekly over 4 weeks, results are provided using a scale of 0-10
To pass the test, the product must achieve a mold growth rating close to 10, indicating minimal to no visible mold growth.
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What is ASTM D3273?
The ASTM D3273 method is one of the key testing standards intended for the accelerated evaluation of an interior coating’s resistance to fungal defacement. It tests the performance of different types of interior coatings by subjecting them to controlled environmental conditions that favor the rapid growth of mold in close simulation of practical usage conditions over an accelerated period.
Interior coatings, including paints, are exposed to environments that encourage the development of mold where moisture content is usually high and ventilation is poor. ASTM D 3273 test method specifies the comparative resistance of coatings over a period of 4 weeks, employing specific temperatures and humidity that favor the growth of mold on test panels.
Scope of ASTM D3273 standard
ASTM D3273 is mainly used to evaluate the mold resistance of
- interior coatings
- paint films
- and other treated surfaces.
ASTM D3273 test conditions & requirements
- Temperature and humidity requirements : The chamber temperature must be maintained at 32.5 ± 1°C (90 ± 2°F). A relative humidity of >93% shall be maintained in the chamber to promote mold growth.
- Substrate and panel preparation : Test panels must be made up of the specified substrates such as softwood sapwood or gypsum board. Two coats of test product must be applied to the test panel. The panel is hung vertically with sufficient space in between for free airflow. The panels must not come in touch with each other or the chamber walls.
- Test duration and monitoring : Panels are monitored for an incubation period of 4 weeks and weekly mold growth is assessed.
ASTM D3273 overview of test method
The test method uses an environmental chamber designed to maintain the high humidity and temperature required for mold growth. The test takes place through the following steps:
- Setting up environmental chamber
Within the chamber, greenhouse soil is placed in a tray and tank is filled with water till it reaches required depth. The chamber is equilibrated, including the soil content and water content, for about 24 hours at approximately 32°C before inoculating the soil. - Fungal inoculation
Fungal suspensions of Aureobasidium pullulans, Aspergillus niger, and Penicillium are prepared and evenly spread over the surface of the greenhouse soil. The fungi are left untouched to sporulate for two weeks before testing. - Test panel preparation and coating application
- Coating material is applied on both the sides and edges of the test panels and allowed to dry for a specific time period
- Placing test panel inside test chamber and incubation
- The panels are hung vertically in the chamber above the sporulae soil tray ensuring enough spacing for airflow. The test panels are exposed for a continuous period of 4 weeks.
- Weekly evaluation of mold growth and ratings
- Panels are assessed for mold growth on a weekly basis for 4 weeks. A rating scale of 0 to 10 is e used to assess the degree of growth on coated panels
Understanding ASTM D3273 results (0-10 rating scale)
Rating scale | % defacement |
10 | No defacement |
9 | 1-10 % defacement |
8 | 11-20 % defacement |
7 | 21-30 % defacement |
6 | 31-40 % defacement |
5 | 41-50 % defacement |
4 | 51-60 % defacement |
3 | 61-70 % defacement |
2 | 71-80 % defacement |
1 | 81-90 % defacement |
0 | 91-100 % defacement |
Test organisms used in ASTM D3273
ASTM D3273 defines Aureobasidium pullulans (ATCC 9348), Aspergillus niger (ATCC 6275), and Penicillium species as the mandatory test organisms. At MIS, additional organisms can be added based on manufacturer’s requirement.
Why do products fail ASTM E3273 testing?
Products can fail ASTM E3273 testing due to many reasons, some of them including:
- Poor antifungal agent formulation– Insufficient concentration of antifungal agent leads to ineffective activity and hence failure.
- Inadequate coating thickness – Thin film or uneven application of coating or insufficient dry film thickness can lead to failure of the coating.
- High moisture absorption – Porous coatings retain water, promoting fungal growth
- Lack of biocidal additives – Absence of mold-inhibiting preservatives or fungistats can directly affect results
Regulatory and industry relevance
ASTM D3273 is not a mandatory regulatory requirement, yet is one of widely recognized standards for evaluating mold resistance in interior environments. This method is widely used by manufacturers, architects, and product developers to support performance claims such as mold or mildew resistant coatings.
ASTM D3273 is typically applicable during different stages such as product development, quality control, and competitive benchmarking to ensure consistent and reliable performance of mold resistance.
In areas such as residential construction, healthcare, and similar areas where indoor air quality and durability are critical, ASTM D3273 test results provide valid confidence to manufacturers and help strengthen positioning of the product in market.
Strengths of ASTM D3273 Test
Products can fail ASTM E3273 testing due to many reasons, some of them including:
- Poor antifungal agent formulation– Insufficient concentration of antifungal agent leads to ineffective activity and hence failure.
- Inadequate coating thickness – Thin film or uneven application of coating or insufficient dry film thickness can lead to failure of the coating.
- High moisture absorption – Porous coatings retain water, promoting fungal growth
- Lack of biocidal additives – Absence of mold-inhibiting preservatives or fungistats can directly affect results
1.Highly controlled conditions:
2. Comprehensive fungal exposure
3. Reliable testing methodology
4. Practical application
Why choose MIS for ASTM D3273 testing?
At Microbe Investigations Switzerland (MIS), we focus on delivering customized and analytical solutions aimed at improving the quality of antifungal coating materials. Leveraging our vast experience in antifungal testing, our team performs ASTM D3273 testing with the highest level of accuracy.
In addition, we also offer ASTM G21 testing for polymeric materials.
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Frequently Asked Questions
DR. Martinoz Scholtz
ASTM D3273 evaluates the mold growth resistance of interior coatings in humid and warm environmental conditions.
Any rating between 8-10 is considered good in ASTM D3273 rating scale ranging from 0-10.
ASTM D3273 typically requires 4-5 weeks.
Products such as Interior coatings, paint films and other treated surfaces can be tested under ASTM D3273 testing.
Mold growth is measured by visual assessment. It is rated on a scale from 0-10, with 0 representing complete defacement and 0 representing no growth.
ASTM D3273 evaluates th resistance of interior paints to mold growth under high humidity conditions. ASTM D3274 assesses the degree of surface defacement by fungal, or algal growth on painted surfaces.
No. ASTM D3273 is designed to test for interior coatings. For exterior coatings, different test methods can be used.
The test is performed with 32.5°C temperature and >93% relative humidity.
ASTM D3273 test verifies claims for mold resistance and ensures reliable performance of coatings in moisture-prone indoor environments.
No, it is a semi-quantitative or qualitative method as the results are not based on microbial counts but a visual rating scale.
The method uses Aureobasidium pullulans, Aspergillus niger and Peniciullium species.
ASTM D3273 is used to assess the mold growth resistance of interior coatings under highly humid and warm conditions whereas ASTM D3274 evaluates the degree of surface defacement by fungal or algal growth on painted surfaces.
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