Copper-Based Preservatives
Copper-based formulations may be used in interior or exterior applications and include the traditional Chromated Copper Arsenate (CCA) and advanced products such as Copper Azole (CA) or Copper Quat (ACQ or Micronized Copper). CA and ACQ have shown a slight increase in corrosion rates on mild steel compared to CCA and Micronized Copper.
In damp or wet environments hot-dip galvanized or stainless steel hardware is strongly recommended in contact with copper-based preservative treated wood. Hot-dip galvanized fasteners should meet ASTM A153. Hot-dip galvanized connectors should meet ASTM A653, Class G185 sheet with 1.85 ounces of zinc coating per square foot minimum.
Type 304 or 316 stainless steel is recommended for maximum corrosion resistance in more severe exterior applications, such as swimming pools or within five miles of salt-water. Stainless steel fasteners are generally required for below-grade applications such as Permanent Wood Foundations. Stainless steel is also a recommended option when CA or Copper Quat formulations are specified at retention levels greater than required for Ground Contact.
Standard carbon-steel, aluminum, or electroplated products must not be installed in direct contact with CA or ACQ treated wood. However, aluminum products may be placed in direct contact with Micronized Copper treated wood when used in interior applications, or exterior applications above ground.1 Electroplated galvanized metal products generally have a thinner layer of protection compared to hot-dip galvanized and are typically not accepted by the building codes for use in exterior applications. Fasteners and connectors used together must be of the same metallic composition to avoid galvanic corrosion (e.g. use hot-dip nails with hot-dip joist hangers).
When aluminum or electroplated hardware must be used in proximity to CA or ACQ treated wood, spacers or physical barriers can protect products such as flashing or termite shields. Barriers should be non-conductive and remain durable for the intended service life of the application. Suitable barriers may include heavy plastic sheeting, rubber, vinyl, or a high quality, non-permeable tar bitumen or epoxy.
Hardware coated with proprietary anti-corrosion technologies is also available. Consult individual hardware manufacturers for specifics regarding their performance.
