Avoid placing zinc in contact with or downstream from acidic woods including oak, red cedar, white cedar, larch, hemlock, or chestnut. Red rosin paper produces an acidic vapor and should never be used as a slip sheet. Further, use only pH-neutral sealants. Also, follow the manufacturer’s recommended storage and handling guidelines.
Glass, aluminum, galvanized steel, stainless steel, painted steel, and most solid, dry building materials present no known compatibility issues with zinc. Electrochemical reactions can cause corrosion when copper is installed above zinc. Chlorides as an additive in mortar or concrete as a bonding agent, or to inhibit freezing are also problematic. The construction team and facility management should protect architectural zinc from acidic cleaning agents, avoid contact with human perspiration, and wear clean gloves when handling and installing the zinc material.
Joints and sealants
The designer should accommodate zinc’s high coefficient of thermal expansion in the design to allow for movement. Caulking is often unnecessary at these critical junctures, which helps lower initial and lifetime costs, and reduces recurring maintenance.
The first consideration at any joint should be how to minimize the use of solder or sealant. Sealants can limit airflow or trap moisture behind the zinc panels and decrease the panel’s lifespan. If soldering is essential, choose one that does not contain lead, cadmium, or copper to maintain zinc’s environmental material attributes, and choose one which LEED and other green building programs recognize.
Resilience and longevity
Properly installed zinc roofing systems will resist air and water infiltration. For regions with high winds and hurricane conditions, zinc roofs satisfied tests to withstand high winds, as per code and local jurisdictional requirements. In areas which are susceptible to fires, zinc also provides a non-combustible solution.
Zinc’s inherent metallic properties allow the material to deliver low-maintenance and long-lasting performance in roofing applications. Runoff from zinc roofs is non-staining and does not adversely affect the environment as zinc’s natural patina forms and minimizes corrosive elements.
Patination process and appearance
Mill finished architectural zinc starts with a bright surface. However, most architects and specification professionals select zinc for its future patina appearance. Like copper, zinc develops its distinctive patina, or surface crust, based on the alloy composition and local environmental conditions.
The patination of architectural zinc occurs through a two-step chemical reaction. First, the zinc combines with water and oxygen to form zinc hydroxide. Then, with carbon dioxide (CO2) in free-flowing air, the zinc generates a dense outer layer insoluble to water and a packed inner layer of alkaline zinc carbonate.
The patina starts forming as zinc carbonate “freckles” start growing together; the rate of its formation is a function of the slope of the surface. Patination will be slower on a vertical roof surface than on a slightly sloped one. Its speed can vary between six months and five years or more, depending on climatic conditions. The more exposure to wetting and drying cycles, the quicker the patina will develop.
