Steel Door Inc.

Avoid Premature Failure of Your Hollow Metal Doors and Frames

Steel is strong. But you need to specify the correct type of steel to ensure your doors and frames perform to their potential. The use of galvannealed coatings on carbon steel sheets can make a major difference in extending the life of doors and frames that are exposed to moisture.

Moisture can get on the exterior surface or inside of a door or frame in several ways:

  • From the top, for example when rain water runs down the side of the building;
  • From the bottom, if there is flooding;
  • Through the hinge and lock preps, with water sprayed from a sprinkler.

Many specifications only call for cold rolled steel doors with factory-applied primer, however this type of coating only protects the outside surface of the door. The raw, uncoated cold rolled material on the inside of the hollow metal door remains unprotected, resulting in the door rusting from the inside out. Galvannealing, used in conjunction with a rust inhibitive factory primer results in a very durable finish.

The iron-zinc coating created in the galvannealing process protects the steel by:

  1. Acting as a barrier between the steel and the environment;
  2. Sacrificing itself if galvanic corrosion occurs.

The iron-zinc coating thickness determines how long protection will be provided, although thicker coatings may result in reduced paint adhesion. The Steel Door Institute recommends A40 and A60 coatings, as a minimum. The heavier A60 coating is recommended for openings where rust is a concern. See SDI 112 (Zinc-Coated Steel Doors and Frames) for more information.

Prevent premature corrosion of your exterior doors and frames by specifying a galvannealed coating. Your clients will be glad you did.