WLFI Adhesive Selection & Application 3 — Questions and Answers
Question 1: A floor inspector finds hollow spots under a glue-down wood floor. Which adhesive application deficiency most commonly causes this?
- Adhesive applied too thick
- Insufficient adhesive coverage or voids in the spread (Correct answer)
- Adhesive cured before planks were laid
- Wrong species of wood used
Correct answer: Insufficient adhesive coverage or voids in the spread
Insufficient or uneven adhesive spread leaves voids beneath planks, resulting in hollow spots detectable by tapping.
Question 2: What does the term 'working time' mean in the context of flooring adhesives?
- Time required for full adhesive cure
- Time the adhesive remains workable after spreading (Correct answer)
- Time flooring can be walked on after installation
- Pot life of a two-component adhesive before mixing
Correct answer: Time the adhesive remains workable after spreading
Working time is the window after spreading during which the adhesive remains pliable enough to accept flooring planks.
Question 3: Which solvent is most commonly associated with VOC concerns in older solvent-based wood flooring adhesives?
- Acetone
- Toluene (Correct answer)
- Isopropyl alcohol
- Mineral spirits
Correct answer: Toluene
Toluene was a common solvent in older flooring adhesives and is a significant VOC and health hazard.
Question 4: When installing solid hardwood over a wood subfloor using adhesive plus mechanical fasteners, what is the inspector verifying by this combination method?
- Compliance with building code load requirements
- Enhanced dimensional stability and reduced movement (Correct answer)
- Adequate moisture vapor control
- Correct species compatibility
Correct answer: Enhanced dimensional stability and reduced movement
Combining adhesive with fasteners limits plank movement, reducing gaps, squeaks, and seasonal dimensional change.
Question 5: A calcium chloride moisture test on a concrete slab yields 4 lbs/1,000 sq ft/24 hrs. According to most adhesive manufacturers, what does this result mean?
- The slab is too wet for any adhesive
- The result is within the acceptable range for most urethane adhesives (Correct answer)
- A moisture-mitigating primer must be applied
- The flooring installation must be postponed for 30 days
Correct answer: The result is within the acceptable range for most urethane adhesives
Most urethane wood flooring adhesives are rated for substrates up to 5 lbs MVER, so 4 lbs is within the acceptable range.
Question 6: Which factor most directly determines the open time of a water-based flooring adhesive on a given job site?
- Plank species
- Ambient temperature and relative humidity (Correct answer)
- Subfloor thickness
- Trowel notch depth
Correct answer: Ambient temperature and relative humidity
High temperature or low humidity accelerates evaporation of the water carrier, shortening the adhesive's open time.
Question 7: During a WLFI inspection, you observe that a laminate floor installed with full-spread adhesive has seams lifting. The adhesive is not tacky at the seam. What is the most likely cause?
- Too much adhesive was applied
- The adhesive skinned over before planks were placed (Correct answer)
- The subfloor was too cold
- Wrong notch trowel was used
Correct answer: The adhesive skinned over before planks were placed
When adhesive skins over before the flooring is placed, bonding fails at the surface, leading to edge and seam lifting.
WLFI Adhesive Selection & Application 3
A floor inspector finds hollow spots under a glue-down wood floor.
Which adhesive application deficiency most commonly causes this?