CTI Movement Joints & Expansion Joints 2 — Questions and Answers
Question 1: What material should be installed inside a movement joint before applying sealant to control joint depth and prevent three-sided adhesion?
- Thinset mortar
- Polyethylene foam backer rod (Correct answer)
- Sanded grout
- Roofing felt
Correct answer: Polyethylene foam backer rod
A polyethylene foam backer rod is inserted into the joint to control sealant depth and prevent three-sided adhesion, allowing the sealant to flex properly under movement.
Question 2: For exterior tile installations, what is the maximum recommended spacing between movement joints per TCNA EJ171?
- 8–12 feet in each direction (Correct answer)
- 16–20 feet in each direction
- 20–25 feet in each direction
- 25–30 feet in each direction
Correct answer: 8–12 feet in each direction
Exterior installations are subject to greater thermal cycling, so TCNA EJ171 requires closer movement joint spacing of 8–12 feet in each direction.
Question 3: A CTI inspector observes a 30×30 foot interior tiled floor with no movement joints anywhere. What deficiency does this represent?
- A cosmetic issue only requiring monitoring
- A code and standards violation with risk of cracking or tile failure (Correct answer)
- Acceptable practice if large-format tiles were used
- Normal for single-family residential floors
Correct answer: A code and standards violation with risk of cracking or tile failure
A 30×30 foot floor without movement joints far exceeds the 20–25 foot maximum spacing required by TCNA EJ171, creating a high risk of tile cracking or delamination.
Question 4: Which material must NEVER be used to fill or close a movement joint in a tile installation?
- Color-matched silicone caulk
- Flexible polyurethane sealant
- Portland cement grout or mortar (Correct answer)
- Urethane joint sealant
Correct answer: Portland cement grout or mortar
Portland cement grout and mortar are rigid and will not flex with movement, defeating the purpose of the joint and causing the surrounding tile to crack or debond.
Question 5: What is the purpose of a 'soft joint' (movement joint) installed at changes in plane, such as where a floor meets a wall?
- To improve the decorative transition between surfaces
- To accommodate differential movement between horizontal and vertical tile planes (Correct answer)
- To reduce the amount of grout needed at corners
- To allow easier removal of tiles during future renovations
Correct answer: To accommodate differential movement between horizontal and vertical tile planes
Changes in plane experience different movement vectors; a soft joint at the transition allows each plane to move independently without cracking either the tile or the substrate.
Question 6: On column bases in a tiled area, where should a CTI inspector verify that movement joints are present?
- Only on the side facing the primary traffic direction
- On all four sides of each column base (Correct answer)
- On the north and south sides only
- Only where the column exceeds 12 inches in diameter
Correct answer: On all four sides of each column base
Columns are restraining elements on all sides, so TCNA EJ171 requires movement joints around the entire perimeter — all four sides — to prevent stress concentration.
Question 7: What is the recommended depth-to-width ratio for sealant within a properly designed movement joint?
- Depth equals width (1:1)
- Depth is twice the width (2:1)
- Depth is half the width (width:depth = 2:1) (Correct answer)
- Depth is three times the width (3:1)
Correct answer: Depth is half the width (width:depth = 2:1)
The sealant depth should be approximately half the joint width (2:1 width-to-depth ratio), enabling the sealant to flex and elongate correctly without failing at the bond line.
CTI Movement Joints & Expansion Joints 2
What material should be installed inside a movement joint before applying sealant to control joint depth and prevent three-sided adhesion?