MRS Building Materials & Mold Growth 3 — Questions and Answers
Question 1: Which factor most significantly accelerates mold growth on wood structural members in a crawl space?
- Direct soil contact
- Lack of natural light
- Absence of mechanical ventilation
- Relative humidity consistently above 70% (Correct answer)
Correct answer: Relative humidity consistently above 70%
Sustained relative humidity above 70% allows moisture to condense on and be absorbed by wood members, providing the water activity necessary for rapid mold growth.
Question 2: What makes paper-faced exterior sheathing (such as DensGlass) more mold-resistant than standard drywall?
- It contains no gypsum core
- It uses fiberglass mat facing instead of paper (Correct answer)
- It is coated with a fungicide during manufacturing
- It has a higher density core
Correct answer: It uses fiberglass mat facing instead of paper
Fiberglass mat-faced sheathings replace the organic paper facing with inorganic fiberglass, eliminating the primary cellulose food source that mold exploits on standard drywall.
Question 3: A remediator encounters mold on the underside of a roof deck in a well-ventilated attic. What is the MOST probable moisture source?
- Roof leaks from damaged shingles
- Air sealing failures allowing humid interior air to enter the attic (Correct answer)
- Groundwater wicking through the foundation
- Condensation on HVAC supply ducts
Correct answer: Air sealing failures allowing humid interior air to enter the attic
In ventilated attics, the most common cause of roof deck mold is warm, moist interior air bypassing insulation and air sealing and condensing on the cooler roof sheathing.
Question 4: Which substrate provides the MOST nutrients for mold and therefore supports the most vigorous growth?
- Galvanized metal ductwork
- Concrete floor slab
- Untreated softwood lumber (Correct answer)
- Ceramic tile
Correct answer: Untreated softwood lumber
Untreated softwood lumber is rich in cellulose and other organic compounds that provide abundant nutrients, supporting aggressive mold colonization when moisture is present.
Question 5: What is the PRIMARY reason carpet is classified as a Category 3 (black water) removal material when flooded with sewage-contaminated water?
- Carpet dye reacts with sewage chemicals
- Carpet fibers cannot be disinfected and the backing traps contamination (Correct answer)
- Carpet adhesive dissolves in sewage water
- Carpet changes color when exposed to sewage
Correct answer: Carpet fibers cannot be disinfected and the backing traps contamination
Carpet and its porous backing cannot be effectively disinfected after sewage exposure, and trapped organic matter and pathogens make it a mold and pathogen reservoir that must be discarded.
Question 6: When assessing mold on ceiling tiles, what property most determines whether cleaning or replacement is appropriate?
- The color of the mold
- Whether the tile is suspended or glued
- The porosity and absorbency of the tile material (Correct answer)
- The age of the ceiling tile
Correct answer: The porosity and absorbency of the tile material
Porous, absorbent ceiling tiles allow mold hyphae to penetrate deep into the material, making surface cleaning ineffective and necessitating replacement.
Question 7: Which statement correctly describes how treated lumber (pressure-treated with preservatives) responds to mold?
- Preservatives make treated lumber completely immune to all mold species
- Treated lumber resists decay fungi but can still support surface mold species (Correct answer)
- Treated lumber absorbs more moisture than untreated, increasing mold risk
- Preservative chemicals are consumed by mold as a food source
Correct answer: Treated lumber resists decay fungi but can still support surface mold species
Pressure-treating preservatives are highly effective against wood-decay fungi but do not prevent surface mold species that obtain nutrients from dust and debris rather than the wood itself.
MRS Building Materials & Mold Growth 3
Which factor most significantly accelerates mold growth on wood structural members in a crawl space?