RRT Subfloor Preparation & Assessment 2 — Questions and Answers
Question 1: Which in-situ test method measures relative humidity within a concrete slab using probes inserted at 40% of slab depth?
- ASTM F1869 calcium chloride test
- ASTM F2170 relative humidity test (Correct answer)
- ASTM D4263 plastic sheet test
- ASTM C1583 tensile adhesion test
Correct answer: ASTM F2170 relative humidity test
ASTM F2170 uses in-situ relative humidity probes placed at 40% slab depth to measure internal moisture conditions in concrete.
Question 2: What minimum thickness of plywood is typically required as an underlayment panel over a board subfloor before carpet installation?
- 1/4 inch
- 3/8 inch (Correct answer)
- 1/2 inch
- 5/8 inch
Correct answer: 3/8 inch
A minimum 3/8-inch plywood underlayment is generally required over skip-sheathing or board subfloors to provide a smooth, stable base for carpet.
Question 3: When testing a subfloor for squeaks, the technician should check fastener spacing. What is the typical maximum fastener spacing for subfloor panels per code?
- 6 inches on edges, 12 inches in the field (Correct answer)
- 8 inches on edges, 16 inches in the field
- 12 inches on edges, 24 inches in the field
- 4 inches on edges, 8 inches in the field
Correct answer: 6 inches on edges, 12 inches in the field
Standard code requires subfloor panel fasteners at 6-inch intervals along edges and 12-inch intervals in the field to prevent movement and squeaks.
Question 4: A technician discovers a low spot of 3/8 inch over a 3-foot span on a concrete subfloor. What is the appropriate repair material?
- Portland cement mortar
- Self-leveling underlayment compound (Correct answer)
- Floor patching caulk
- Gypsum-based joint compound
Correct answer: Self-leveling underlayment compound
Self-leveling underlayment compound is the correct choice for filling low spots on concrete subfloors as it flows to a flat finish and bonds to concrete.
Question 5: What is the primary purpose of the ASTM D4263 plastic sheet test for subfloors?
- To measure the pH level of concrete
- To detect the presence of moisture in or below the subfloor (Correct answer)
- To determine the compressive strength of the slab
- To test adhesive bond strength
Correct answer: To detect the presence of moisture in or below the subfloor
The ASTM D4263 plastic sheet test is a qualitative method for detecting moisture beneath or within a concrete slab using a taped plastic sheet.
Question 6: When encountering an existing cutback adhesive residue on a concrete subfloor, the recommended approach for carpet reinstallation is to:
- Remove all residue by mechanical grinding before proceeding
- Skim coat over the residue with an appropriate embossing leveler (Correct answer)
- Apply solvent to dissolve the residue completely
- Install carpet directly over the residue without treatment
Correct answer: Skim coat over the residue with an appropriate embossing leveler
Encapsulating cutback adhesive residue with a compatible skim coat or embossing leveler is the recommended method, as grinding may release asbestos fibers in older adhesives.
Question 7: Which condition in a crawl space most directly contributes to subfloor moisture problems above?
- Inadequate ventilation and exposed ground soil (Correct answer)
- Too many floor joists
- Low ceiling height in the crawl space
- Absence of insulation between joists
Correct answer: Inadequate ventilation and exposed ground soil
Inadequate ventilation combined with exposed soil allows ground moisture to evaporate upward into the crawl space and penetrate the subfloor.
RRT Subfloor Preparation & Assessment 2
Which in-situ test method measures relative humidity within a concrete slab using probes inserted at 40% of slab depth?