Waterproofing Stucco Walls Before Backfilling: A Critical Step

The Scenario

Lois plans to fill a sunken yard (60×40 ft, 6+ ft deep) to create a Mexican courtyard. Fill will contact a 3-ft concrete foundation and 2 ft of elastomeric Sto-coated wall above. A raised Trex deck will cover the fill near the wall. Concern: moisture migration through fill to the stucco, plus snakes/rodents in unfilled gaps.

Initial Advice

If fill rises within 8 inches of the interior finished floor, hire a professional to design a waterproofing system. Crawl spaces/basements below grade are less risky.

Follow-Up: Contractor Confusion

Contractors disagree: some say Sto is a water barrier; others warn against below-grade use. Suggestions include tar, “Storm Guard” (self-adhesive roofing membrane), or nothing. The wall has a 3.5-ft porch roof; fill extends 6+ ft out under deck/patio.

Expert Clarification

Sean Murphy: Landscape category addresses drainage/grading, not architectural waterproofing product specs. Without site visit, construction details, and local soil data, recommending specific membranes is unwise. Consult a local architect or waterproofing specialist. Every product suits different substrates, exposures, and conditions.

Takeaway

Backfilling against stucco walls demands a site-specific waterproofing design by a qualified professional. General advice: ensure positive drainage away from structure, use dimple board/drainage mat, and confirm membrane compatibility with Sto.