CFI Subfloor Assessment & Preparation 5 — Questions and Answers
Question 1: When assessing an existing subfloor for a new flooring installation, what is the FIRST step a CFI installer should perform?
- Apply a skim coat of leveling compound
- Conduct a visual and physical inspection for structural integrity, moisture, and flatness (Correct answer)
- Sand the entire surface
- Install a new layer of underlayment immediately
Correct answer: Conduct a visual and physical inspection for structural integrity, moisture, and flatness
A thorough inspection must precede any preparation work to identify all deficiencies and develop the correct remediation plan.
Question 2: What is the minimum compressive strength required for a self-leveling underlayment used beneath ceramic tile?
- 1,500 psi
- 2,500 psi
- 3,000 psi (Correct answer)
- 4,500 psi
Correct answer: 3,000 psi
Self-leveling underlayments used under tile must achieve a minimum of 3,000 psi compressive strength to withstand point loads without cracking.
Question 3: A subfloor is found to have localized soft spots where the wood is spongy underfoot. What does this indicate?
- The plywood grade is insufficient
- Moisture damage or rot has compromised the panel's structural integrity (Correct answer)
- The panels were installed without adhesive
- The joist spacing is too wide
Correct answer: Moisture damage or rot has compromised the panel's structural integrity
Spongy areas indicate delamination or rot from moisture intrusion, requiring panel replacement rather than surface patching.
Question 4: What product is used to fill wide cracks (over 1/4 inch) in a concrete slab before flooring installation?
- Self-leveling underlayment
- Hydraulic cement or epoxy filler (Correct answer)
- Thin-set mortar
- Latex floor patch
Correct answer: Hydraulic cement or epoxy filler
Wide cracks require a rigid hydraulic cement or epoxy crack filler to prevent movement from telegraphing through the finished floor.
Question 5: What is the ASTM standard that governs the use of the anhydrous calcium chloride test for measuring moisture vapor emission from concrete?
- ASTM F710
- ASTM F1869 (Correct answer)
- ASTM F2170
- ASTM E1745
Correct answer: ASTM F1869
ASTM F1869 is the standard test method for measuring moisture vapor emission rate (MVER) of concrete floors using anhydrous calcium chloride.
Question 6: Which fastener type provides the best holding power in a wood subfloor to minimize panel movement and squeaks?
- Smooth-shank nails
- Drywall screws
- Ring-shank nails or screws (Correct answer)
- Staples
Correct answer: Ring-shank nails or screws
Ring-shank nails and screws have mechanical interlock with wood fibers, dramatically increasing withdrawal resistance compared to smooth-shank fasteners.
Question 7: If a concrete subfloor has a cure-and-seal compound applied that tests as bond-breaking, what is the correct remediation sequence?
- Apply bonding primer directly over the sealer
- Mechanically scarify the surface, vacuum debris, then test adhesion again (Correct answer)
- Etch with muriatic acid and rinse thoroughly
- Install a floating floor system to avoid bonding
Correct answer: Mechanically scarify the surface, vacuum debris, then test adhesion again
Mechanical scarification physically removes the sealer, and adhesion testing after cleaning confirms the surface is ready for the chosen installation system.
CFI Subfloor Assessment & Preparation 5
When assessing an existing subfloor for a new flooring installation, what is the FIRST step a CFI installer should perform?