Add another advantage to the long list of benefits of several R-Guard fluid-applied building envelope products: proven resistance to mold and fungal growth. The following products have passed ASTM C1338, Test Method for Determining Fungi Resistance with zero fungi growth:
Spray Wrap MVP (including Spray Wrap Rain Screen)
Cat 5 (including Cat 5 Rain Screen and Cat 5 ICF)
FastFlash (gun-grade and roller-grade)
Fungal growth in buildings isn’t just an aesthetic problem — it’s a performance problem, a durability problem and, most importantly, a human health problem. Wherever moisture and air leakage intersect inside a building assembly, conditions become favorable for mold and fungal growth. In today’s high-performance buildings, where tighter envelopes are the norm, preventing that growth is essential to delivering structures that are both efficient and healthy.
From a health perspective, fungi introduce airborne spores into indoor environments, which can negatively affect indoor air quality and have been associated with allergic reactions, respiratory irritation, and asthma-related symptoms. Because humans spend a large majority of their time indoors, the materials used to construct and seal a building envelope play a direct role in the quality of the air people breathe every day. Healthy buildings begin with assemblies that resist becoming sources of contamination.
Fungal growth also threatens the physical integrity of a building. Many fungi break down organic materials found throughout wall systems, including wood components and paper-faced substrates. Over time, this biological activity can weaken assemblies, reduce adhesion between materials, and accelerate deterioration. Even when structural elements remain intact, mold growth often signals unmanaged moisture — one of the primary drivers of premature building failure.
That’s where ASTM C1338, Test Method for Determining Fungi Resistance, becomes meaningful. This test evaluates whether a material supports fungal growth under controlled conditions. When products like Spray Wrap MVP (including Spray Wrap RS), Cat 5 (including Cat 5 Rain Screen and Cat 5 ICF), Fast Flash (gun- and roller-grade), Joint & Seam Filler, Board Seam Filler WB, AirDam, and Targeted Interior Air Seal pass ASTM C1338 with zero fungal growth, it confirms that these materials do not serve as a food source for fungi.
For airtight building envelopes, that distinction matters. Air barriers and flashing materials sit at critical transition points where air, vapor and moisture management converge. Products that resist fungal growth help reduce the risk of concealed mold within assemblies, supporting healthier indoor air quality while maintaining long-term performance.
Ultimately, passing ASTM C1338 reinforces a broader goal: building enclosures that last longer, perform as intended, and contribute to safer indoor environments. When enclosure materials resist fungal growth, they help protect both the people inside the building and the durability of the structure itself — advancing a more resilient and sustainable built environment.
