CFI Subfloor Assessment & Preparation 3 — Questions and Answers
Question 1: Subfloor panels should be installed with a gap between panel edges. What is the recommended gap size?
- 1/16 inch
- 1/8 inch (Correct answer)
- 1/4 inch
- 3/8 inch
Correct answer: 1/8 inch
A 1/8-inch gap between panel edges allows for seasonal expansion and prevents panel buckling.
Question 2: Which subfloor defect is MOST likely to cause ridging or telegraphing through sheet vinyl flooring?
- Low spots deeper than 3/16 inch
- Exposed panel edges or fastener heads that are proud (Correct answer)
- Panels with improper span rating
- Subfloor panels installed with grain running the wrong direction
Correct answer: Exposed panel edges or fastener heads that are proud
Proud fasteners or panel edges create hard points that telegraph directly through thin resilient sheet goods.
Question 3: What is the correct fastener pattern when installing a second layer of plywood underlayment over an existing subfloor?
- Fasten only at the perimeter
- Fasten at 6 inches on center in the field and 4 inches at edges (Correct answer)
- Fasten at 12 inches on center throughout
- Fasten only through existing fastener locations
Correct answer: Fasten at 6 inches on center in the field and 4 inches at edges
Closer edge fastening (4") prevents edge movement and peaking, while 6" field fastening provides adequate substrate stiffness.
Question 4: Before installing flooring over a radiant heat subfloor system, what is the maximum substrate surface temperature allowed during installation?
- 65°F
- 75°F
- 85°F (Correct answer)
- 95°F
Correct answer: 85°F
Most manufacturers require the radiant heat system be operating and surface temperature not exceed 85°F during installation to prevent adhesive or material issues.
Question 5: A concrete slab has an alkalinity (pH) reading of 11. What is the significance for flooring installation?
- No concern; all adhesives tolerate high pH
- High pH can break down adhesive bonds and require primer or mitigation (Correct answer)
- High pH indicates the slab is too dry
- High pH improves adhesion for most products
Correct answer: High pH can break down adhesive bonds and require primer or mitigation
Concrete pH above 9 can chemically attack certain adhesives, making pH testing and appropriate primer selection critical.
Question 6: When grinding down a high spot on a concrete slab, what safety equipment is mandatory?
- Hearing protection only
- Respirator, eye protection, and hearing protection (Correct answer)
- Eye protection and knee pads only
- Chemical-resistant gloves and apron
Correct answer: Respirator, eye protection, and hearing protection
Concrete grinding generates silica-laden dust, requiring respiratory protection (N95 minimum), plus eye and hearing protection.
Question 7: What does an L/360 deflection rating mean for a subfloor system?
- The subfloor can deflect up to 360 mm under load
- The span length divided by 360 equals the maximum allowable deflection (Correct answer)
- 360 pounds per square foot is the load capacity
- The floor joists must be 360 mm deep
Correct answer: The span length divided by 360 equals the maximum allowable deflection
L/360 means the maximum allowable mid-span deflection is the joist span length divided by 360, a common benchmark for tile installations.
CFI Subfloor Assessment & Preparation 3
Subfloor panels should be installed with a gap between panel edges.
What is the recommended gap size?