Moisture and thermal movement

After the firing process bricks absorb moisture from the atmosphere and expand irreversibly, up to a maximum of 0.1%. It is therefore recommended that bricks should not be used for at least two weeks after firing, (although it is now recognised that this irreversible process may continue at a decreasing rate for 20 years). Subsequent moisture and thermal movements are largely reversible and movement joints allowing for a 1 mm movement per 1 m of brickwork should be allowed, typically at 10-12 m centres and at a maximum of 15 m, in restrained walls. Unrestrained or lightly restrained walls should have movement joints at 7-8 m centres. Horizontal movement joints should be at approximately 12 m intervals, as the vertical movement is of the same order as movement in the horizontal direction.

For many buildings the necessary movement joints can be made inconspicuous by careful detailing or featured as part of the design. Appropriate locations for movement joints would be where differing structural forms adjoin, such as abutments between walls and columns or where the height or thickness of a wall changes; alternatively, at design details such as brickwork returns, re-entrant corners, or the recesses for downpipes. In expansion joints, fillers such as cellular polythene, polyurethane or foam rubber should be used, as these are easily compressible. Pointing should be with a flexible sealing compound such as two-part polysulfide.

Typical reversible moisture movement = 0.02% Typical reversible thermal movement = 0.03% Thermal movement = 5-8 X 10~6 deg

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