Details, not surfaces
Most waterproofing failures happen at junctions rather than in the middle of a surface: around drains, at wall upstands, at door thresholds, around penetrations and at movement joints.
Age and workmanship
Membranes and coatings have a limited life, especially under strong sun. Overlapping repairs, coatings applied over tiles without preparation, and drains not bonded to the membrane are frequent findings.
Before choosing a solution
Understanding exactly where and why water enters helps avoid replacing a whole terrace when a detail is at fault, or patching a detail when the whole system has reached the end of its life.
