Joint Sealant Design and Application

About this course.

Buildings need movement joints because every material in them changes dimension over time, and because the structure itself deflects, settles and vibrates. If two building elements are rigidly joined and then forced to move relative to one another, something has to give: a crack opens, a tile debonds, a pane cracks, or a rigid mortar joint spalls. A movement joint is a deliberate gap that lets adjacent elements move independently, and a flexible sealant is what closes that gap to weather while still stretching and compressing as the joint works. Understanding the sources of movement tells you where joints belong and how much they must accommodate.

The most universal source is thermal movement. Materials expand when heated and contract when cooled, and they do so at different rates. A dark metal cladding panel in full Australian summer sun can reach a surface temperature far above the shaded air temperature, then cool sharply overnight; over that daily cycle it expands and contracts measurably. Concrete, masonry, glass, aluminium and timber each have their own coefficient of thermal expansion, so where dissimilar materials meet, differential movement is guaranteed. Long runs of the same material also accumulate significant total movement simply because the effect scales with length — a long parapet, a long run of coping or a long cladding elevation moves more end-to-end than a short one.