ASTM 5590:

The word “resistant” is often used loosely in the construction materials market. From “water-resistant” watches to “fire-resistant” drywall, the term implies a level of protection that may or may not be backed by rigorous scientific data. When it comes to mold, the stakes are too high for linguistic ambiguity. For Protective Coatings Group (PCG), the gold standard for proving that a coating actually does what it claims is the ASTM 5590 test.

What is ASTM 5590?

The American Society for Testing and Materials (ASTM) developed the D5590 protocol to provide a standardized, aggressive method for determining how well a coating prevents fungal growth. Unlike consumer-grade “mildew resistant” tests that might only look at surface discoloration, ASTM 5590 is a “challenged” test.

During the process, treated samples are placed in a controlled environment with high humidity and optimal temperatures for mold growth. The samples are then inoculated with high concentrations of aggressive fungal strains, such as Aspergillus niger and Penicillium citrinum. The test doesn’t just wait for spores to land naturally; it forces the spores onto the surface to see if they can survive.

The “Zero Growth” Rating

The results of an ASTM 5590 test are measured on a scale of 0 to 4:

• 0: No growth observed on the sample.

• 1: Trace growth (less than 10%).

• 2: Light growth (10% to 30%).

• 3: Medium growth (30% to 60%).

• 4: Heavy growth (60% to 100%).

For a building to be truly “fortified,” anything other than a 0 rating is a failure. Many organic “anti-microbial” paints will achieve a 0 rating initially, but if you run the test again after the coating has “aged” or been exposed to moisture, the rating often slips to a 1 or 2 as the biocides leach out. FortiCel, thanks to its inorganic silica cross-link technology, is designed to maintain that 0 rating for decades because the protection is a mechanical property of the film, not a temporary chemical additive.

Why Builders Should Demand Test Data

When selecting a mold prevention partner, builders should look past the marketing brochures and ask for the lab reports. A “proprietary blend” that hasn’t been subjected to ASTM 5590 is a liability. By insisting on products that have passed this specific standard, developers protect themselves from future litigation. If an issue ever goes to court, having a documented “0 rating” on the structural components is a powerful piece of evidence that the builder followed the highest possible standards of care.

Key Technical Takeaways:

• Aggressive Inoculation: The test proves the coating works even in worst-case scenarios.

• Standardized Metrics: It allows for an apples-to-apples comparison between different products.

• Long-Term Reliability: Focus on coatings that maintain their 0 rating over time, not just in a “fresh” state.