CTI CTI Substrate Preparation & Waterproofing 1 — Questions and Answers
Question 1: What is the maximum allowable floor deflection for a substrate intended for tile installation per TCNA guidelines?
- L/180
- L/360 (Correct answer)
- L/240
- L/120
Correct answer: L/360
TCNA specifies the substrate must not deflect more than L/360 of the span under live load for tile installations.
Question 2: Which moisture test measures vapor emission rate in pounds per 1,000 sq ft per 24 hours on a concrete slab?
- Relative humidity probe test
- Calcium chloride test (Correct answer)
- Phenolphthalein test
- ASTM F2170 probe
Correct answer: Calcium chloride test
The calcium chloride test (ASTM F1869) measures vapor emission rate in pounds per 1,000 sq ft per 24 hours.
Question 3: What is the maximum acceptable moisture content for a wood subfloor before tile installation?
- 25%
- 15%
- 19% (Correct answer)
- 10%
Correct answer: 19%
Wood subfloors should have a moisture content of 19% or less to prevent warping or bond failure beneath tile.
Question 4: Which type of waterproofing membrane is applied as a liquid and cures to form a seamless, continuous layer?
- Sheet membrane
- Foam backer rod
- Bonded (liquid-applied) waterproofing membrane (Correct answer)
- Cleavage membrane
Correct answer: Bonded (liquid-applied) waterproofing membrane
Bonded liquid-applied waterproofing membranes are brushed or rolled on and cure to form a seamless, continuous barrier with no seams.
Question 5: What is the primary purpose of a cleavage membrane in a mortar bed installation?
- Bond the tile directly to the subfloor
- Allow the mortar bed to float independently of the substrate (Correct answer)
- Provide electrical grounding for heated floors
- Increase the thermal R-value of the assembly
Correct answer: Allow the mortar bed to float independently of the substrate
A cleavage membrane (such as 15 lb felt or 4-mil polyethylene) separates the mortar bed from the substrate, allowing independent movement.
Question 6: When inspecting a shower pan liner installation, how high must the liner extend above the rough shower curb?
- 1 inch
- 2 inches (Correct answer)
- To the top of the tile
- 3 inches above the shower floor
Correct answer: 2 inches
The liner must extend at least 2 inches above the top of the rough curb to ensure proper waterproofing containment.
CTI CTI Substrate Preparation & Waterproofing 1
What is the maximum allowable floor deflection for a substrate intended for tile installation per TCNA guidelines?