Stucco Water Damage: Signs of Water Behind Your Stucco

Why is water seeping through my wall when it rains, but there is no leak?

Because stucco is not a sealed skin. The Northwest Wall & Ceiling Bureau (NWCB) starts its guidance on water-resistive barriers from this: “It is assumed that some incidental moisture will penetrate the outer most cladding of cement plaster (stucco) the same as brick, wood or other sidings.” In a sound wall, that water reaches the water-resistive barrier, runs down it and leaves at the weep screed at the bottom. Oregon’s code is written around the same idea: the wall must be built “in a manner such that water entering the assembly can drain to the exterior.”

Water gets into the building, or damages the framing, when that path fails. NWCB names the usual places: “penetrations through the stucco membrane such as windows, doors, vents, decks, etc. and cracks wider than what is termed ‘hairline’”. And when it investigates leaking buildings, the finding is consistent: “Investigations into leaking buildings are invariably the result of poor or inadequate flashings or a failure to properly lap flashings and/or WRB.” So a wall can let water in during rain with no single obvious hole: the gap is often in the flashing around an opening, or in how the layers behind the stucco were lapped.

Portland’s rain makes this a practical question; the Portland stucco repair page has the rainfall figures and the code that applies in the metro counties.

How water damage hides

The trade’s guidance is to evaluate the wall before a repair is scoped. What can show on the surface:

• A bubbling or blistering finish. Sika: “Blistering or bubbling of stucco finish is often caused by water that has gotten behind the finish.”
• Wider cracks. Cracks larger than 1/32 inch “could present issues with moisture intrusion and contribute to blistering and/or peeling of finishes” (Sika). See stucco cracks.
• Trouble at the base of the wall. Stucco carried down onto concrete, or a weep screed buried below grade, gives water nowhere to go.

EIFS houses and the barrier problem

EIFS is a separate case. Barrier EIFS, the first kind used in the United States, relies “on keeping the moisture completely out of the system”, with no drainage behind it. EIMA’s own account of the EIFS problem is that “The origin of the EIFS problem was due to poor construction practices such as leaking windows, improper flashing around the roof, the deck, and the chimney.” NWCB’s verdict: “Barrier EIFS cannot and probably should not have been used on wood framed structures with little or no protection from rain.” From November 1, 1999, the criteria for an ICBO (International Conference of Building Officials) evaluation report required a tested drainage EIFS on wood-frame residential buildings (NWCB 600-406). If your house has EIFS, see EIFS repair.

What happens next

The order matters: find out how far the water has gone, then decide the repair.

1. Evaluation. A stucco inspection, which can mean opening a small part of the wall at a crack or around a window to see the substrate and the barrier.
2. Repair or remediation. If the damage is local, a stucco repair may be enough. If water has reached the sheathing or framing, the wall is opened, the wet material repaired, and the barrier, drainage space and flashing rebuilt: that is stucco remediation.
3. Flashing. Oregon requires kick-out flashing at every wall and roof intersection, and the barrier laps over the weep screed’s flange so water exits at the base.

Skip the coating as a fix. NWCB “does not believe elastomeric coatings should be used to solve water intrusion problems cause by inadequate flashings.”