CTI CTI Waterproofing & Moisture Management 1 — Questions and Answers
Question 1: According to TCNA guidelines, which areas in a residential shower MUST have a waterproofing membrane?
- Only the shower floor
- Only the lower 6 inches of walls
- The entire shower floor and walls to at least 3 inches above the highest water point (Correct answer)
- Only behind the tile on the back wall
Correct answer: The entire shower floor and walls to at least 3 inches above the highest water point
TCNA requires waterproofing on all shower walls to at least 3 inches above the highest water source to prevent moisture intrusion behind the tile.
Question 2: What is the purpose of a pre-slope under a shower mortar bed?
- To provide decorative texture
- To direct water toward the drain and prevent pooling beneath the tile (Correct answer)
- To increase the floor height
- To add structural support
Correct answer: To direct water toward the drain and prevent pooling beneath the tile
The pre-slope creates a sloped mortar layer beneath the liner so water that penetrates the tile system drains to the weep holes rather than pooling.
Question 3: What minimum slope is required on a shower floor for proper drainage according to TCNA standards?
- 1/16" per foot
- 1/4" per foot (Correct answer)
- 1/2" per foot
- 1" per foot
Correct answer: 1/4" per foot
TCNA recommends a minimum slope of 1/4" per foot toward the drain to ensure standing water does not accumulate on the shower floor.
Question 4: Which type of waterproofing membrane is applied as a liquid and then becomes a continuous flexible sheet when cured?
- CPE (chlorinated polyethylene) liner
- PVC sheet membrane
- Liquid-applied topical membrane (Correct answer)
- Foam backer board
Correct answer: Liquid-applied topical membrane
Liquid-applied membranes are brushed or rolled on and cure to a seamless waterproof sheet that conforms to any shape.
Question 5: What is the function of weep holes in a clamping-ring shower drain?
- To increase water flow speed
- To allow moisture trapped between the liner and mortar bed to drain out (Correct answer)
- To prevent clogs
- To anchor the drain to the liner
Correct answer: To allow moisture trapped between the liner and mortar bed to drain out
Weep holes sit at the level of the liner and allow any water that seeps through the tile system to escape into the drain instead of pooling beneath the mortar bed.
Question 6: Why should a PVC or CPE shower liner never be installed on top of a cured mortar bed without a slip sheet?
- It would prevent drainage
- Sharp mortar particles can puncture the liner during installation or from foot traffic over time (Correct answer)
- It would prevent bonding of the top mortar layer
- It would cause efflorescence
Correct answer: Sharp mortar particles can puncture the liner during installation or from foot traffic over time
A slip sheet of roofing felt or 15-lb. felt protects the liner from sharp mortar aggregate that could puncture and compromise the waterproof barrier.
CTI CTI Waterproofing & Moisture Management 1
According to TCNA guidelines, which areas in a residential shower MUST have a waterproofing membrane?