Sealants are an alternative to solder where additional strength is not required. In most cases, sealants should not be necessary with a properly designed copper installation. They are at best a relatively short-term solution requiring frequent maintenance. Regardless, sealant-filled joints have been used successfully as a secondary waterproofing measure for standing seam and batten seam roofing applications where low-sloped roofs are less than . Sealants can also be used in joints that are primarily designed to accommodate thermal movement of the copper.
The sealants used should be tested by the manufacturer and designated as compatible for use with copper.
In general, butyl, polysulfide, polyurethane, and other inorganic or rubber-based sealants are reasonably compatible with copper. Acrylic, neoprene, and nitrile-based sealants actively corrode copper. Silicone sealants are somewhat successful with copper but their suitability should be verified before application.