Copper And Aluminum Corrosive Gutter Flashing

The discharge from drain pipes on rooftop air conditioning units can be very corrosive particularly if the piping is copper and the drainage goes into galvanized steel scuppers conductor heads or gutters.

Copper and aluminum corrosive gutter flashing.

Bituminous or zinc chromate primers can be used between copper and aluminum. In the event of roof renewals where lead already exists and its re use is desirable. Aluminum will be very susceptible to galvanic corrosion in contact with copper assuming that the two metals are also in contact with a common electrolyte such as water with some ionic content almost any text or handbook on corrosion will have galvanic series table. Additionally the use of galvanized nails screws flashing or drip edge on copper roofing or copper gutters should likewise be avoided as such less noble fasteners and metals will corrode rapidly.

Salts increase the electrical conductivity of water. Either of these or a red lead primer can be effective in separating copper from iron and other ferrous metals. Use aluminum flashing and fasteners in contact with aluminum copper flashing and copper nails with copper roofing gutters etc. The farther two metals or alloys are separated on the table faster the corrosion of the less noble of the two will be when they are in contact.

Anodized aluminum is considered compatible with all other metals. For example never use copper or lead flashings with aluminum zinc or galvanized roofing materials. When this is not possible choose a second metal that is not likely to lead to galvanic corrosion or use a physical barrier to separate the two metals. Even water dripping from a copper flashing upstream of a steel or aluminum flashing or gutter can lead to corrosion of the coated steel or aluminum roofing materials.

For example rain water run off from a copper roof going into aluminum gutters and downspouts will result in traces of copper salts in the run off wash accelerating corrosion of the aluminum. Pure zinc or aluminum are suitable alternatives although neither are as workable as lead. For example rain water run off from a copper roof going into aluminum gutters and downspouts will result in traces of copper salts in the run off wash accelerating corrosion of the aluminum.