Stucco Cracks: Which Ones Matter and How They Are Repaired

Are cracks in stucco normal?

Some cracking, yes. Cement stucco behaves like concrete in this respect. The Northwest Wall & Ceiling Bureau (NWCB) says portland cement plaster is “always susceptible to the occasional hairline crack no matter how good the design, installation and mix used.” Sto’s specification agrees: “Some degree of cracking is normal in portland cement stucco and should be expected.” Sika goes further on the most common kind, the cracks at the corners of windows and doors: “cracks of this kind are not indications of substandard plasterwork or materials, and should not lead to assumptions that the stucco will not perform properly.”

Normal is not the same as harmless, though. The question is what kind of crack you have.

Hairline or wider: the 1/32-inch line

Sika’s repair procedure gives a practical threshold. Cracks of 1/32 inch or smaller “represent more of an aesthetic nuisance”. Cracks larger than that “could present issues with moisture intrusion and contribute to blistering and/or peeling of finishes.” NWCB says the same thing from the other side: most cracks “are hairline and are only a cosmetic problem and tests combined with field experience has proven they typically pose no significant threat to moisture intrusion.”

The shape matters too. A long, straight vertical or horizontal crack through the stucco “would be a sign of stress relief and may indicate a place where a joint originally should have been incorporated” (Sika). Sto adds that such a crack, left unrepaired, lets the stucco “continue to deteriorate, creating an enlarged path for water intrusion”.

How each kind is repaired

There is no single crack repair. Sika’s procedure says the method should be chosen by “the size/ severity of the cracks and their root cause”. In practice that means:

• Hairline cracks are mostly cosmetic. NWCB notes that elastomeric coatings “can also be used to hide hairline cracks”, with maintenance, vapor permeability and thickness issues to weigh first, and that elastomeric paint “will limit the options of repairs” later.
• Wider and through cracks are repaired in the stucco itself, as part of a stucco repair, with the patch matched to the wall as closely as it allows. NWCB is honest that a perfect match “may be difficult to impossible” and that “A hairline crack may appear between the patch and existing wall.”
• Cracks with water behind them are a different job. A coating will not fix a flashing leak: NWCB “does not believe elastomeric coatings should be used to solve water intrusion problems cause by inadequate flashings.” That is a stucco inspection first, then a repair or remediation.

Once the building is stable, a repaired crack usually stays closed: “If the building is stable and settled, most cracks should not return” (NWCB 600-611). Control joints help limit new cracking but, as NWCB points out, “do not guaranty against cracking.”

Cracks in EIFS are a different question

Synthetic stucco (EIFS) is not cement plaster, and its manufacturers disagree about cracks. Sto: “Cracks are not a normal occurrence in EIFS.” Dryvit: “Most hairline cracks are aesthetic and result from normal building movement.” Both agree the cause comes first; Dryvit’s repair guide says “Before proceeding, the exact cause of cracks should be determined.” See EIFS repair.

For questions about cracks you cannot read yourself, Sika’s advice is to engage “a qualified engineering firm for further investigation.” If water may be involved, the stucco water damage page shows the other signs to look for.