Movement Joint Spacing — Masonry Reference

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.

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.

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.

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.