How to Avoid Contact With Aluminum & Dissimilar Metals

ex logo

This is provided to inform clients of the dissimilar metal protection requirements of the 2015 Aluminum Design Manual, Chapter M – Section M.7


Structures of the alloys covered by the Aluminum Design Manual are not ordinarily painted. Surfaces shall be painted where:

  • 2014-T6 alloys are exposed to corrosive environments.
  • Aluminum alloy parts are in contact with, or are fastened to, uncoated steel members or other dissimilar materials (see below).
  • Exposed to extremely corrosive conditions.
  • Required by the designer for reason of appearance.

Either the aluminum or the dissimilar material must be painted, sealed, or otherwise protected from contact with the following materials:

    • STEEL
      • Exceptions: No protection required for:
        • Stainless Steel (300 series), except in high-chloride (salty) environments.
        • Galvanized Steel (hot-dip galvanized or electro-galvanized).
        • Aluminized steel.
      • Acceptable Paints:
        • Priming Paint (one coat), such as zinc molybdate, alkyd type primer in accordance with Federal Specification TT-P-645B (“good quality”, no lead content).
        • Follow primer with two coats of paint consisting of 2 lb. of aluminum paste pigment (ASTM Specification D962-81, Type 2, Class B) per gallon of varnish meeting Federal Specification TT-V-8 1, Type 11, or equivalent.
        • Severe Corrosion Conditions: Additional protection can be obtained by applying a suitable sealant to the faying surfaces, capable of excluding moisture from the joint during prolonged service in addition to the zinc molybdate, alkyd type primer.


    • WOOD
      • Includes aluminum laid on or against:
        • Wood
        • Fiberboard
        • Other porous materials that absorb water and cause corrosion (i.e. where moisture is present and corrodents will be entrapped between the surfaces).
      • Acceptable Protection:
        • Heavy coat of alkali resistant bituminous paint or other coating providing equivalent protection before installation.
        • Other insulating barrier between the aluminum and the porous material.
    • CONCRETE, Embedded into
      • Exceptions:
        • Concrete with no corrosive additives – no protection required.
        • Where no extended exposure to extremely corrosive conditions is expected – no protection required.
      • Acceptable Paints:
        • Priming Paint (one coat), such as zinc molybdate primer in accordance with Federal Specification TT-P-645B (“good quality”, no lead content).
        • Alt: Heavy coating of alkali resistant bituminous paint.
        • Alt: Wrap aluminum with a suitable plastic tape applied in such a manner as to provide adequate protection at the overlaps.
      • NOTE: Aluminum shall not be embedded in concrete to which corrosive components such as chlorides have been added if the aluminum will be electrically connected to steel.
      • WATER that has come in contact with a heavy metal (e.g. copper)
        • Heavy metals leached into water can cause corrosion of aluminum.
        • Acceptable Remedies:
          • Paint the heavy metal.
          • Coat the heavy metal with plastic.
          • Divert drainage from heavy metal away from aluminum.

Prepainted aluminum only requires additional protection when specified by the designer to abate extremely corrosive conditions.

Information provided by Zach Rubin, PE


Last Update: December 15, 2022  

March 9, 2021  Codes & Standards, Engineering  
Total 4 Votes:

Tell us how can we improve this post?

+ = Verify Human or Spambot ?

Scroll to Top