Do wall/ledge joints move?
The wall/ledge joint is considered a movement joint for various reasons.
A common cause of joint movement between the wall and ledge is the shrinkage of supporting timber floor joists during the drying out period which is most dramatic after new construction works. When floor joists shrink, the ledge drops down causing the wall/ledge joint to expand.
Another cause joint movement between the wall and ledge is the settlement of bath and shower receptors under the additional load of water and occupant. When receptors settle down the wall/ledge joint expands. Weight settlement is most dramatic in semi-ridged receptors made from materials such as acrylics.
Settlement and deflection of weak floor boards and joist under weight can occur in old buildings, especially at the impact point of supporting bath and shower receptor legs. When floor boards settle down, the ledge drops down causing the wall/ledge joint to expand.
Joint movement occurs as a result of shrinkage in surrounding timber stud walls during the drying process, again most frequent after new construction works. When timber studs shrink, the wall pulls back causing the wall/ledge joint to expand along the horizontal axes.
Other common causes of wall/ledge joint movement can be attributed to the unique nature of the hostile shower environment where materials exposed to high moisture and thermal fluctuations will expand and contract at different rates, creating stress at meeting joints if not accommodated during the design and build period.