Match wet and dry observations

Use observations from similar viewpoints and comparable drying stages. Was the earlier image taken before rain, immediately afterward or after a long dry period? A spreading stain below an unchanged source suggests transport. A newly exposed cavity or detached coating is different evidence. Keep these descriptions separate so the reviewer can distinguish change in appearance from an actual change in the affected material or protective surface.

Trace recurring water paths

Note whether runoff repeatedly emerges at the same edge and whether adjacent surfaces dry sooner. A persistent source may point toward trapped water, a sheltered joint or a leak, while an isolated splash has a different implication. Do not create a water-spray test to reproduce the symptom without the supplier-approved assessment method. Such a test may introduce exposure that does not resemble normal rain or may reach sensitive equipment.

A stain growing sideways after one rainfall event may show where water spread rather than where corrosion advanced. A measured cavity becoming deeper under comparable examination is materially different evidence. The report should avoid using these two observations as interchangeable growth measures.

Decide what needs measurement

If the concern is growth, request a qualified comparison based on physical extent or loss rather than stain intensity. If the concern is water routing, request examination of the actual path and affected barrier. Cleaning can improve visibility only when compatible and authorized; it does not prove the source has ended. An engineer must establish any condition limits for the identified part, and a wet appearance alone cannot supply them.