Movement Joints & Expansion Joints Flashcards

What material should be installed inside a movement joint before applying sealant to control joint depth and prevent three-sided adhesion?

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.

For exterior tile installations, what is the maximum recommended spacing between movement joints per TCNA EJ171?

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.

A CTI inspector observes a 30×30 foot interior tiled floor with no movement joints anywhere. What deficiency does this represent?

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.

Which material must NEVER be used to fill or close a movement joint in a tile installation?

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.

What is the purpose of a 'soft joint' (movement joint) installed at changes in plane, such as where a floor meets a wall?

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.

On column bases in a tiled area, where should a CTI inspector verify that movement joints are present?

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.

What is the recommended depth-to-width ratio for sealant within a properly designed movement joint?

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.