To limit the probability of inadequate strength to resist the stresses induced by the thermal expansion and contraction of masonry chimneys, which could lead to the delamination or cracking of stucco under gravity, wind or impact loads, or freeze-thaw stresses.
Where stucco provides required protection from precipitation, 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 leakage of carbon monoxide gas into living space, which could lead to the acute poisoning or asphyxiation of persons.