Expansion and movement joints explained

Where you find them

• Vertical joints in long runs of brickwork or blockwork, often near corners and openings.
• Joints in render and insulated render (EWI) systems.
• Movement joints in large tiled floors and walls, including at perimeters and over structural joints.
• Expansion joints between buildings, decks and slabs.

Why the sealant fails

• Age and sunlight: sealant hardens and stops stretching.
• The wrong product: a high-modulus or non-movement sealant in a joint that moves a lot.
• Wrong depth: a bead that is too deep or too shallow tears or loses adhesion.
• No bond breaker: if the sealant sticks to the back of the joint as well as the sides, it cannot stretch.
• Dirty or crumbling joint edges.

Doing it properly

1. Cut out the old sealant and any old backing.
2. Clean the joint faces and let them dry.
3. Insert a closed-cell backing rod at the right depth, which also acts as a bond breaker.
4. Prime the joint faces if the sealant manufacturer says so.
5. Apply a movement-rated sealant and tool it to the correct profile.

When to call a specialist

If joints keep failing, are much wider than they should be, or cracks are appearing in the wall beside them, the problem may be structural rather than the sealant. An applicator can reseal, but ask an engineer to look at ongoing movement. For resealing work, read about expansion and movement joint sealing or post a movement joint job.

Quick answers

Can a movement joint be filled with mortar?

No. Filling it with a rigid material stops it working, and the wall will usually crack somewhere else.

How is movement joint work priced?

Usually per metre, plus access. See the price guide for general ranges.