A band of stucco at the base of every wall is chronically damp long after rain. What is the likely mechanism?

A damp band that runs along the base of every wall and persists after the surrounding surface has dried is a location clue, not a material clue. Anything wrong with the mix or the coating would show up in patches wherever the defect occurred, not in a stripe at a consistent height above grade. That geometry points to water arriving from below: stucco in contact with soil, or terminating without the weep screed that is supposed to stop the wall short of grade and let absorbed water drain out. Once the wall wicks, moisture moves up through the assembly by capillary action and keeps the base saturated long after rainfall. The consequence behind the stucco is what matters — sustained moisture at the base of the wall reaches sheathing and framing, which is where decay begins.

A uniform damp band at the base indicates moisture wicking up from the soil, typically because the stucco extends to or below grade or because the weep screed that should terminate and drain the assembly is missing. The pattern follows the ground line, which is what identifies the source as below rather than within the wall.

Stucco is a reservoir cladding that absorbs water and needs a path to drain and dry. A weep screed at the base terminates the assembly above grade and allows absorbed moisture to exit. Stucco continuing into soil bridges that termination and lets ground moisture wick upward.

Patches come from the wall. A Band Means Below — if the wetness draws a level line above the dirt, the ground is feeding it.

Moisture questions are usually solved by geometry, not chemistry. Where the water is tells you where it came from.

• •Blaming the mix or the finish coat for a pattern that follows grade
• •Treating persistent base dampness as normal drying
• •Overlooking that the concealed sheathing behind the band is the actual risk