Why Do Metal Doors Rot?


Why Do Metal Doors Rot - rusted door in New OrleansEver wonder why lots of metal doors in New Orleans and the surrounding areas are rotted-off at the bottom?  Obviously, they didn’t use a B&M galvannealed door!”
Seriously though, it’s a common question and there are a few major factors why metal doors rot. As you may have noticed, the weather here in New Orleans, Louisiana has very high humidity all year round. It could also be that the doors were not galvanized or galvannealed. Maybe they didn’t get a finish coat of paint over the primer coating or the wrong type of paint was used. In any case moisture has entered the interior of the door and collected at the bottom instead of passing through the door or evaporating as intended.

Poor Paint Coverage

You can install a Cold Rolled Steel (CRS) door on the exterior of a building.  However, in New Orleans humidity, you won’t have that door for long. Properly painting all six sides of the door with a Direct To Metal (DTM) paint will help a CRS door slow the rot process.  However, even a perfectly painted CRS door will not last as long as a properly painted Galvanized or Galvannealed door.

Galvanized or Galvannealed?

Why Do Metal Doors Rot - Rotting Door in New OrleansGalvannealed or galvanneal results from the combined process of galvanizing and annealing (heating a material, maintaining temperature and then slowly cooling) to produce specialized sheets of steel. Galvanization is made through the hot-dipping process and an immediate in-line annealing and gives a very fine greyish matte finish. Galvanneal does not flake off when formed, stamped, and bent. The very fine matte finish acts like a primer, allowing paint to adhere easily, and is very rust proof. Galvanneal sheets offer good paintability, weldability, corrosion resistance, and formability as well as a long reliable service life.

B & M’s Door Stock

B & M stocks Cold Rolled Steel drywall frames for interior use only. However, for external use, all our stock metal doors and masonry frames start with CRS material but then are Galvannealed (A60) for exterior use as well as interior. We can also order our metal products Galvanized (G90).

B & M’s stock galvannealed steel doors & frames are fabricated from carbon steel sheets that have been coated with zinc on both sides by the continuous hot-dip process and then heat-treated. This coating is referenced with an “a” designation (A60). If your construction requires, we can order galvanized steel doors & frames fabricated from carbon steel sheets that have been coated with zinc on two sides by the continuous hot-dip process. This coating is referenced with a “g” designation (G90). Of course both galvannealed and galvanized doors and frames are available prime painted.

Right Material for the Job

Just remember that for exterior applications starting with a Galvanized or Galvannealed door and frame is best but as mentioned above combining it with properly painting both sides of the door and all four edges and painting the frame with a DTM paint before hanging adds the most protection. This combination will ensure that your customer will be able to have the benefits of the longest life span possible for the metal doors and frames. Your benefit is receiving a great reputation with your clients for using material that lasts a long time.

Have Questions?
A cheap or poorly installed metal door doesn’t stand a chance in our harsh, tropical environment. We love answering questions about metal doors and helping our customers choose the right products to ensure they don’t wind-up with a rotten door.

Have questions about how to avoid winding up with a rotten door?  Contact us today!