CMI CMI Building Materials & Construction Systems 1 — Questions and Answers
Question 1: Why is gypsum wallboard (drywall) considered a high-risk material for mold growth in water-damaged buildings?
- The paper facing and gypsum core absorb water readily and provide a nutrient source for mold (Correct answer)
- Drywall contains antimicrobial additives that fail after 5 years
- Gypsum board only supports mold growth if it contains recycled content
- Only the painted surface of drywall is susceptible to mold, not the core
Correct answer: The paper facing and gypsum core absorb water readily and provide a nutrient source for mold
Drywall's paper facing is cellulose-based, providing an ideal nutrient substrate for mold, and the gypsum core readily absorbs and retains water, creating persistent moisture conditions for growth.
Question 2: At what moisture content (MC%) does wood framing typically become susceptible to mold and decay fungus growth?
- Above 19% moisture content (Correct answer)
- Above 8% moisture content
- Above 30% moisture content
- Wood framing is not susceptible to mold at any moisture content
Correct answer: Above 19% moisture content
Wood moisture content above 19% (some references cite 19–20%) creates conditions favorable to mold and rot fungi, as fungi require free moisture in the wood fiber to metabolize.
Question 3: Which type of insulation is most resistant to mold growth due to its non-organic composition?
- Closed-cell spray polyurethane foam (SPF) (Correct answer)
- Cellulose insulation
- Fiberglass batt insulation
- Cotton batt insulation
Correct answer: Closed-cell spray polyurethane foam (SPF)
Closed-cell spray polyurethane foam is an inert, non-porous, non-cellulosic material that does not absorb water or provide nutrients for mold, making it the most mold-resistant insulation type.
Question 4: A mold inspector finds mold growth behind vinyl wallcovering in a hotel corridor. What building science principle explains this common problem?
- Vinyl acts as a vapor barrier trapping moisture between the wall and the covering, creating hidden mold growth (Correct answer)
- Vinyl wallcovering is a food source for mold species
- The adhesive used under vinyl wallcovering introduces moisture into the wall
- This only occurs when the HVAC system is set too cold
Correct answer: Vinyl acts as a vapor barrier trapping moisture between the wall and the covering, creating hidden mold growth
Vinyl wallcovering is impermeable to water vapor, trapping moisture that diffuses through the wall from humid outdoor air against the cool gypsum substrate, creating hidden mold growth.
Question 5: What makes oriented strand board (OSB) sheathing more susceptible to mold than traditional plywood in similar conditions?
- OSB's higher moisture absorption rate and longer drying time compared to plywood (Correct answer)
- OSB contains more wood preservatives that attract mold
- Plywood has a porous surface that dries faster than the smoother OSB face
- OSB and plywood have identical mold resistance properties
Correct answer: OSB's higher moisture absorption rate and longer drying time compared to plywood
OSB absorbs moisture more rapidly at its edges and retains it longer than plywood due to its compressed strand construction, making it more prone to swelling, delamination, and mold growth when wet.
Question 6: Which concrete or masonry characteristic makes it susceptible to mold growth despite being an inorganic material?
- Dust and organic debris accumulate on porous masonry surfaces, providing nutrients for mold to grow (Correct answer)
- Masonry contains organic lime that mold can metabolize directly
- Concrete emits water vapor that directly feeds mold colonies
- Mold cannot grow on concrete under any circumstances
Correct answer: Dust and organic debris accumulate on porous masonry surfaces, providing nutrients for mold to grow
While concrete and masonry are not direct food sources for mold, their porous surfaces collect dust, dirt, and organic material, and they can hold moisture, creating suitable conditions for mold growth on the deposited organic layer.
CMI CMI Building Materials & Construction Systems 1
Why is gypsum wallboard (drywall) considered a high-risk material for mold growth in water-damaged buildings?