To limit the probability of excessive corrosion, which could lead to inadequate support for stucco or swelling of expanded metal stucco mesh, which could lead to delamination, disintegration or cracking under gravity, wind or impact loads, or freeze-thaw stresses.
Where stucco is applied to masonry chimneys, this is to limit the probability of precipitation or meltwater ingress, which could lead to the premature failure of chimney liners, which could lead to the escape of heat or flames, which could lead to the ignition of combustible building components, which could lead to harm to persons.