Q Efflorescence developed in several walls shortly after their construction. We think this efflorescence is primarily associated with construction moisture.
How long should we wait before cleaning the efflorescence off the masonry?
A Efflorescence that occurs shortly after construction is often referred to as “new building bloom.” If you clean this efflorescence off too early, the construction moisture may not have evaporated yet and the problem will reappear.
Also, the cleaning process itself will introduce water into the masonry, which could contribute to future efflorescence. In some cases, the efflorescence will wash off during rains. Therefore, I recommend waiting several months following construction before cleaning.
The time of the year that the cleaning is completed may actually be more important in preventing the return of efflorescence than the length of time after the masonry was installed. Efflorescence problems are more common following periods of cool weather because it takes longer for the water to evaporate. If water remains in the wall for extended periods, salts and soluble compounds in the mortar and brick dissolve and slowly migrate to the wall surface.
If the efflorescence is cleaned off in the summer during hot/dry weather, the moisture associated with the cleaning process can dry quickly, which reduces the risk that the efflorescence will return. On the other hand, if efflorescence is cleaned off in the late fall, the walls may not fully dry until the return of warm weather in the spring, which can result in additional efflorescence.
If the efflorescence includes calcium carbonate deposits, some mild acid will be needed to remove the staining. If an acid is used, the wall should be thoroughly wetted first to prevent absorption of the acid into the masonry. Buffered solutions are preferred over diluted muriatic acid since they are less likely to contribute to additional efflorescence.
As with any moisture problem in brick masonry, it is essential that all sources of water penetration are eliminated before the efflorescence is removed. The pattern of efflorescence often provides a good indication of the source of water penetration. New building bloom is often distributed across the face of the masonry, while efflorescence caused by water penetration is usually concentrated below sills and copings, and at through-wall masonry flashings.