MRS Building Materials & Mold Growth 2 — Questions and Answers
Question 1: Which property of oriented strand board (OSB) makes it more susceptible to mold than plywood?
- Higher resin content
- Greater moisture absorption due to exposed wood strands (Correct answer)
- Lower density
- Smoother surface finish
Correct answer: Greater moisture absorption due to exposed wood strands
OSB absorbs moisture more readily than plywood because the exposed wood strands on its surface and edges wick water, providing ideal conditions for mold colonization.
Question 2: What is the approximate minimum equilibrium moisture content at which most mold species can begin colonizing wood framing?
- 8%
- 12%
- 19% (Correct answer)
- 25%
Correct answer: 19%
Wood framing at or above 19% moisture content provides sufficient water activity for most mold species to begin active colonization and growth.
Question 3: Which building material component is the PRIMARY food source for mold growing on painted drywall?
- The latex paint coating
- The paper facing of the gypsum board (Correct answer)
- The gypsum core
- The primer layer
Correct answer: The paper facing of the gypsum board
The paper facing on gypsum board contains cellulose, which mold readily digests, while the gypsum core itself provides little organic nutrition for mold growth.
Question 4: A remediation specialist finds mold on concrete block walls. What is the most likely reason concrete supports mold growth?
- Concrete itself is an organic food source
- Dust, dirt, and organic debris deposited on the surface provide nutrients (Correct answer)
- Concrete absorbs water and becomes food for mold
- High calcium content feeds mold colonies
Correct answer: Dust, dirt, and organic debris deposited on the surface provide nutrients
Concrete is inorganic and not itself a food source, but dust and organic debris that accumulate on concrete surfaces supply the nutrients mold needs to colonize.
Question 5: Which type of insulation is considered LEAST susceptible to mold growth?
- Cellulose insulation
- Fiberglass batt insulation
- Cotton batt insulation
- Spray polyurethane foam (closed-cell) (Correct answer)
Correct answer: Spray polyurethane foam (closed-cell)
Closed-cell spray polyurethane foam is both inorganic and impermeable to moisture, making it highly resistant to mold colonization compared to fiber-based insulations.
Question 6: When mold grows on HVAC ductwork lined with fiberglass, what is the preferred remediation approach according to EPA guidance?
- Apply an EPA-registered disinfectant and leave in place
- HEPA vacuum and wipe with damp cloth
- Remove and replace the affected duct sections (Correct answer)
- Apply encapsulant coating over the mold
Correct answer: Remove and replace the affected duct sections
EPA guidance recommends removing and replacing porous duct liner materials with mold growth rather than attempting to clean them, as mold hyphae penetrate the fibers and cannot be fully removed.
Question 7: What characteristic of vinyl wallcovering contributes to behind-wall mold problems in humid climates?
- Vinyl releases nutrients that feed mold
- Vinyl acts as a vapor barrier trapping moisture against the drywall (Correct answer)
- Vinyl adhesive contains organic compounds mold consumes
- Vinyl has microscopic pores that allow mold spores through
Correct answer: Vinyl acts as a vapor barrier trapping moisture against the drywall
Vinyl wallcovering is vapor-impermeable and can trap moisture condensing on or migrating to the drywall face, creating ideal hidden mold conditions behind the covering.
MRS Building Materials & Mold Growth 2
Which property of oriented strand board (OSB) makes it more susceptible to mold than plywood?