Weathering steel does not perform well when corrosive airborne chemicals are abundant. The patina is rapidly consumed and the steel corrodes at rates approximated to that of unprotected steel. • Chemicals can be aggressive to HDG steel as well, but only after a number of years will the entire zinc coating be consumed. HDG steel is often painted in order to achieve a long-lasting coating to protect the substrate steel.The buildup of vegetation and organic material on and around weathering steel concentrates moisture. Constant exposure to moisture is adverse to the patina and excessive corrosion will occur. HDG steel is unaffected by the presence of vegetation or organic material.