The base coat in stucco (both traditional and EIFS, or synthetic stucco) is a cementitious material. Because of the composition and nature of cement, salts that are naturally present within the material can be drawn out with water or moisture. Wikipedia defines Efflorescence as:
In chemistry, efflorescence (which means “to flower out” in French) is the loss of water (or a solvent) of crystallization from a hydrated or solvated salt to the atmosphere on exposure to air.
“to flower out” in French. How romantic.
Efflorescence occurs in stucco when it is not properly protected with a finish coating, either because it was improperly applied or when water has seeped in from another source. The damage – while initially only aesthetic – can lead to further decay of the finish coat and base coat. It’s an indicator that water is getting in from somewhere, and should not be there. The base coat in stucco should never be exposed to water.
Efflorescence is like a cancer that spreads rapidly, causing more extensive damage if left untreated. Before doing any stucco repairs, the root cause of the problem must first be addressed. Is the water entering from another location, perhaps above the stucco?, at the soffit? Through an improperly sealed window or hose bib?
Once the root cause has been fixed, the extent of the damage must be evaluated. Does the system need to replaced right through the insulation, or just the base coat and finish coat? Stucco repairs aren’t just a one-size fits all. Though a full replacement of the wall will fix nearly any problem, this is typically overkill and far more expensive than is actually required. A qualified stucco / EIFS inspector, manufacturer rep or reputable contractor will help you determine what needs to be done. While going back to the original contractor to get it repaired under warranty is the best bet, ensure that the EIFS manufacturer gets involved – after all, it’s in their best interest to get it repaired as cheaply and inexpensive as possible.