Why do masonry walls need movement joints?

All masonry materials expand and contract due to temperature changes, moisture variations, and (for clay bricks) irreversible moisture expansion after firing. Without movement joints, these dimensional changes create stress that causes cracking — typically at corners, around openings, and at changes in height or thickness. Movement joints provide controlled locations where the wall can move without cracking.

What is the difference between expansion and contraction joints?

Clay bricks expand after manufacture (irreversible moisture expansion) and also with temperature increases, so movement joints in clay brickwork are expansion joints — they start closed and open slightly over time. Concrete blocks and calcium silicate bricks shrink after manufacture as they dry out, so their movement joints are contraction joints — they start slightly open and close. This distinction affects the initial joint width and filler material.

How wide should a movement joint be?

For clay brickwork, a typical movement joint width is 10-13mm, designed to accommodate 1mm per metre of wall length (approximately). For concrete blockwork, 10mm is standard. The joint must be wide enough for the sealant to function — most flexible sealants require a minimum 10mm width and a depth of half the width (5mm for a 10mm joint). A closed-cell polyethylene backer rod is fitted behind the sealant to control depth.

Do I need movement joints in internal walls?

Internal walls generally experience smaller temperature and moisture changes than external walls, but long runs of blockwork (e.g., corridors) still benefit from movement joints. As a guide, internal concrete blockwork should have joints at not more than 9m centres. Internal clay brickwork can typically go to 15m centres. Where an internal wall abuts an external wall, a vertical movement joint (or slip tie connection) may be needed at the junction.

Movement Joint Spacing — Masonry Reference

Maximum spacing for movement joints in clay brick, concrete block, and calcium silicate masonry. Width calculations, sealant requirements and joint profiles.

Movement Joint Spacing by Material

Reference: BS EN 1996-2, PD 6697, BS 5628-3 (withdrawn but still referenced).

Masonry Material	Max Spacing (m)	Max from Corner (m)	Movement Type
Clay bricks (external)	12	6 (max 7.5)	Expansion
Clay bricks (internal)	15	7.5	Expansion
Concrete blocks (external)	6	3	Contraction
Concrete blocks (internal)	9	4.5	Contraction
Calcium silicate bricks	7.5 – 9	3.75 – 4.5	Contraction
Natural stone (ashlar)	12 – 15	6	Expansion

Additional Locations for Movement Joints

At changes in wall height or thickness
At setbacks or returns in plan
Adjacent to columns or structural frames
At each side of window and door openings in long walls (if near the maximum spacing)
Where different masonry materials meet (e.g., clay over concrete block)
At junctions between new and existing construction
At every floor level change in multi-storey construction

Joint Construction Details

Component	Specification
Joint width	10-13mm for brickwork, 10mm for blockwork
Backer rod	Closed-cell polyethylene foam, 25% larger than joint width
Sealant depth	Half the joint width (min 6mm, max 12mm)
Sealant type	Low modulus silicone or polysulphide to BS EN ISO 11600
Compressible filler	Flexible foam strip (for expansion joints in cavity)
Wall ties at joints	Debonding sleeves or sliding ties to allow movement

Note: Spacings shown are general guidance. Actual spacing depends on exposure, restraint conditions, and the specific coefficient of thermal and moisture expansion for the product used. Refer to BS EN 1996-2 and PD 6697 for definitive guidance.

See the Brick Bond Patterns, the Mortar Suction Rates, and the Weep Hole Spacing guide.