WLFI Moisture Testing & Subfloor Preparation 2 — Questions and Answers
Question 1: What is the acceptable moisture content range for a wood subfloor before installing solid hardwood flooring in most US climates?
- Below 19%
- 6–9% (Correct answer)
- 12–15%
- 20–25%
Correct answer: 6–9%
Wood subfloors should be between 6–9% MC to be within acceptable range for solid hardwood installation in most US climates.
Question 2: When using a calcium chloride test (ASTM F1869) on a concrete slab, results are expressed as:
- Percent relative humidity (%RH)
- Pounds of moisture per 1,000 sq ft per 24 hours (lbs/1000 sf/24h) (Correct answer)
- Grams per square meter per hour
- Parts per million (ppm)
Correct answer: Pounds of moisture per 1,000 sq ft per 24 hours (lbs/1000 sf/24h)
ASTM F1869 calcium chloride tests report moisture vapor emission rate (MVER) in pounds per 1,000 square feet per 24 hours.
Question 3: A concrete slab shows an in-situ RH reading of 82% at a depth of 40% of the slab thickness. What is the inspector's recommended action?
- Proceed with installation immediately
- Apply a moisture mitigation system before flooring installation (Correct answer)
- Increase HVAC ventilation for 24 hours then retest
- Sand the surface to open pores
Correct answer: Apply a moisture mitigation system before flooring installation
An RH reading above 80% (ASTM F2170 threshold for most adhesives) requires a moisture mitigation system before flooring is installed.
Question 4: Which of the following subfloor conditions would MOST likely cause laminate flooring panels to buckle after installation?
- Subfloor flatness within 3/16" over 10 feet
- Excess moisture in the subfloor exceeding manufacturer limits (Correct answer)
- Perpendicular joist spacing of 16" on center
- Subfloor panels fastened with ring-shank nails
Correct answer: Excess moisture in the subfloor exceeding manufacturer limits
Excess moisture causes laminate core materials to swell, leading to buckling or peaking at panel joints.
Question 5: Before installing a floating laminate floor over a concrete slab, the inspector discovers multiple hairline cracks. What is the primary concern?
- Hairline cracks create noise during foot traffic only
- Cracks allow moisture vapor to migrate upward from below the slab (Correct answer)
- Hairline cracks reduce adhesive bond strength
- The cracks indicate the slab needs full replacement
Correct answer: Cracks allow moisture vapor to migrate upward from below the slab
Hairline cracks in slabs act as pathways for moisture vapor to migrate upward, potentially damaging the flooring above.
Question 6: A wood I-joist subfloor system is tested and found to have localized moisture damage. Which repair approach is most appropriate before new flooring is installed?
- Apply a coat of polyurethane sealer over the damaged area
- Sister new joists alongside damaged ones and replace the compromised sheathing (Correct answer)
- Install a second layer of underlayment to bridge the weak spot
- Proceed with installation and monitor for deflection
Correct answer: Sister new joists alongside damaged ones and replace the compromised sheathing
Sistering new joists and replacing damaged sheathing restores structural integrity that moisture-compromised I-joists can no longer provide.
Question 7: How long must calcium chloride test dishes remain sealed on the concrete surface per ASTM F1869?
- 8 hours
- 16 hours
- 60–72 hours (Correct answer)
- 96 hours
Correct answer: 60–72 hours
ASTM F1869 requires calcium chloride dishes to remain sealed on the surface for a minimum of 60 to 72 hours before weighing.
WLFI Moisture Testing & Subfloor Preparation 2
What is the acceptable moisture content range for a wood subfloor before installing solid hardwood flooring in most US climates?