Stucco Problems: Cracks, Leaks and Water Behind the Wall

Cosmetic, or a way in for water?

The stucco problems covered here sort into two groups: cosmetic, or a possible path for water.

Usually cosmetic. Hairline cracks. The Northwest Wall & Ceiling Bureau (NWCB) says cement stucco is “always susceptible to the occasional hairline crack no matter how good the design, installation and mix used”, and that most cracks “are hairline and are only a cosmetic problem”. Sika’s repair procedure puts the line at 1/32 inch: smaller cracks “represent more of an aesthetic nuisance”. Stucco cracks covers how to tell them apart.

Worth investigating. Cracks wider than 1/32 inch, long straight cracks and a lot of cracking; a bubbling or blistering finish, which Sika says “is often caused by water that has gotten behind the finish”; and water getting in around windows, doors, vents or decks. Stucco water damage covers how water gets behind stucco and what it looks like.

What is the most serious problem with exterior stucco?

Water getting behind it. NWCB’s guidance on water-resistive barriers starts from the assumption that “some incidental moisture will penetrate the outer most cladding of cement plaster (stucco) the same as brick, wood or other sidings”, which is why the barrier and flashing behind the stucco are the backup. When NWCB looks at buildings that leak, “Investigations into leaking buildings are invariably the result of poor or inadequate flashings or a failure to properly lap flashings and/or WRB.”

That is why NWCB advises a full evaluation “by qualified persons prior to making any decisions for final scope of repairs.” If you see the signs above, a stucco inspection is the place to start.