What exterior work may involve
Depending on the foundation and water problem, exterior work may include exposing the wall, cleaning and repairing the surface, applying waterproofing materials, improving drainage near the footing, and backfilling the excavation.
Why exterior drainage matters
A wall coating alone does not control where groundwater goes. Drainage at the footing and sensible surface-water management can be important parts of an exterior strategy.
Interior or exterior?
Interior drainage may be less disruptive in many situations, while exterior work can address the outside face of the foundation directly. The better fit depends on access, wall condition, water source, and project goals.