CTI Tile Installation Techniques 3 — Questions and Answers
Question 1: When installing tile over radiant heat cables, which trowel ridge orientation is required?
- Trowel ridges must run parallel to the heat cables
- Trowel ridges must run perpendicular to the heat cables (Correct answer)
- Trowel ridges should be applied in a swirl pattern
- Ridge orientation does not matter with radiant heat systems
Correct answer: Trowel ridges must run perpendicular to the heat cables
Running trowel ridges perpendicular to heat cables ensures the mortar collapses over the cables when tiles are set, preventing air voids that cause cracking and uneven heat distribution.
Question 2: What is the maximum allowable variation in substrate flatness for tiles with any edge greater than 15 inches, per ANSI A108.02?
- 3/16" in 10 feet and 1/8" in 2 feet (Correct answer)
- 1/4" in 10 feet and 1/16" in 2 feet
- 1/2" in 10 feet and 3/16" in 2 feet
- 1/8" in 10 feet and 1/32" in 2 feet
Correct answer: 3/16" in 10 feet and 1/8" in 2 feet
ANSI A108.02 requires surfaces receiving tile with edges over 15" to be flat within 3/16" in 10 feet and 1/8" in any 2-foot span to minimize lippage.
Question 3: A CTI installer is tiling a wet area wall using the thin-set method. At what point during installation should silicone caulk be applied at the tub/tile junction?
- Before tile installation, as a backer for the first tile row
- After all tile is set and fully cured, in place of grout at the change-of-plane joint (Correct answer)
- Simultaneously with grouting all joints
- Only after the grout has been sealed
Correct answer: After all tile is set and fully cured, in place of grout at the change-of-plane joint
Change-of-plane joints (floor-to-wall, tub-to-wall) must be filled with a flexible sealant like silicone after tile and mortar fully cure, replacing grout which would crack from differential movement.
Question 4: Which layout method is preferred when centering tile in a room with an off-center focal point such as a fireplace?
- Center the tile field to the room dimensions
- Center the tile layout to the focal point feature (Correct answer)
- Start from the most visible corner and work outward
- Use a diagonal layout to draw attention away from the focal point
Correct answer: Center the tile layout to the focal point feature
When a strong focal point like a fireplace exists, centering the tile layout on that feature creates visual balance and symmetry at the most-viewed area of the room.
Question 5: What does the term 'lippage' refer to in tile installation?
- Mortar squeeze-up between tiles at the joint
- Vertical displacement between the edges of adjacent tiles (Correct answer)
- The curved edge profile on rectified tile
- Grout staining at tile edges due to efflorescence
Correct answer: Vertical displacement between the edges of adjacent tiles
Lippage is the vertical height difference between the edges of adjacent tiles; ANSI A108.02 limits allowable lippage based on joint width and tile size.
Question 6: When installing tile on a wood subfloor, what minimum combined thickness of subfloor layers is typically required to prevent deflection-related failures?
- 3/4"
- 1"
- 1-1/8" (Correct answer)
- 1-1/2"
Correct answer: 1-1/8"
The Tile Council of North America (TCNA) W411 method requires a combined subfloor/underlayment thickness of at least 1-1/8" to provide sufficient stiffness to prevent tile and grout cracking.
Question 7: A tile installer notices that Portland cement mortar is beginning to skin over before tiles are placed. What should be done?
- Mist the mortar surface with water to reactivate it
- Scrape off the skinned mortar and apply fresh material (Correct answer)
- Press the tile firmly into the skinned mortar — it will bond under weight
- Apply a liquid bonding agent over the skinned surface and proceed
Correct answer: Scrape off the skinned mortar and apply fresh material
Skinned mortar has lost its open time and will not bond properly; the affected area must be scraped clean and fresh mortar applied before setting tile.
CTI Tile Installation Techniques 3
When installing tile over radiant heat cables, which trowel ridge orientation is required?