CFI Moisture Mitigation Systems 4 — Questions and Answers
Question 1: What is the difference between a vapor barrier and a vapor retarder in flooring applications?
- There is no difference; the terms are interchangeable
- A vapor barrier has a perm rating of 0.1 or less; a vapor retarder has a higher perm rating but still limits transmission (Correct answer)
- A vapor barrier is installed under the slab; a vapor retarder is installed on top
- A vapor retarder is a liquid-applied product; a vapor barrier is always a sheet product
Correct answer: A vapor barrier has a perm rating of 0.1 or less; a vapor retarder has a higher perm rating but still limits transmission
A vapor barrier (≤0.1 perms) provides near-total moisture blockage, while a vapor retarder has a higher perm rating that slows but does not completely stop vapor transmission.
Question 2: When installing a polyethylene sheet vapor retarder over a concrete slab before glue-down hardwood, what is the minimum recommended overlap at seams?
- 2 inches
- 6 inches
- 12 inches (Correct answer)
- 24 inches
Correct answer: 12 inches
Sheet vapor retarders should overlap at seams by a minimum of 12 inches and be taped or sealed to prevent moisture from passing through the joints.
Question 3: A concrete slab is only 60 days old. Why is this a concern for flooring installation?
- Young concrete is too soft to support foot traffic
- Newer concrete still contains significant residual construction moisture that hasn't fully dried (Correct answer)
- Concrete below 90 days cannot be tested for moisture
- Young slabs do not accept adhesives properly due to alkalinity
Correct answer: Newer concrete still contains significant residual construction moisture that hasn't fully dried
Concrete retains water from the mixing process (free water) for months; slabs under 90–180 days typically still have elevated moisture that can damage flooring.
Question 4: What role does concrete porosity play in moisture mitigation system selection?
- Higher porosity concrete requires less surface preparation
- Highly porous concrete may require a primer or additional coat to prevent the mitigation product from soaking in unevenly (Correct answer)
- Porosity has no effect on mitigation system performance
- Low-porosity concrete is always the worst candidate for mitigation coatings
Correct answer: Highly porous concrete may require a primer or additional coat to prevent the mitigation product from soaking in unevenly
Very porous concrete can absorb a mitigation coating unevenly, leaving thin spots; a primer or extra coat ensures consistent film thickness and effective moisture control.
Question 5: Which of the following is a crystalline waterproofing technology that works by forming insoluble crystals within concrete pores?
- Polyurethane membrane
- Chlorinated rubber coating
- Cementitious crystalline treatment (e.g., Xypex, Kryton) (Correct answer)
- Acrylic latex sealer
Correct answer: Cementitious crystalline treatment (e.g., Xypex, Kryton)
Cementitious crystalline treatments react with water and cement minerals to form insoluble crystals that block capillary pores and reduce moisture transmission through the slab.
Question 6: What condition must be met before performing moisture testing on a newly placed concrete slab according to ASTM standards?
- The slab must be at least 7 days old
- The slab must have cured for a minimum of 28 days
- The slab must reach the same temperature as the occupied space (HVAC operational for 48+ hours) (Correct answer)
- The slab must be coated with a curing compound first
Correct answer: The slab must reach the same temperature as the occupied space (HVAC operational for 48+ hours)
ASTM standards require that the slab and the test environment be at service conditions (HVAC operational, building enclosed) for at least 48 hours before testing for accurate results.
Question 7: A moisture mitigation coating manufacturer's spec sheet states the product covers 200 sq ft per gallon per coat with two coats required. How many gallons are needed for a 2,000 sq ft area?
- 5 gallons
- 10 gallons
- 20 gallons (Correct answer)
- 40 gallons
Correct answer: 20 gallons
At 200 sq ft/gallon per coat × 2 coats, each gallon covers 100 sq ft total; 2,000 sq ft ÷ 100 sq ft/gallon = 20 gallons.
CFI Moisture Mitigation Systems 4
What is the difference between a vapor barrier and a vapor retarder in flooring applications?