How often do you notice and think about what the door you’re walking through is made of? After this post, you might find yourself thinking about it a bit more.
What are Doors Made of?
Commercial doors can be made with a variety of materials. Most door and frame assemblies are a mixture of materials like wood, metal, and glass. Like these office doors with glass.
Most commercial metal doors, also called hollow metal or steel doors, are made with steel. They aren’t made with stainless steel, but a form of treated carbon steel called galvannealed steel, which shouldn’t be confused with galvanized.
While the doors we call metal or steel aren’t stainless steel, you can find stainless steel doors for high-humidity areas like kitchens. There are also aluminum doors, like our storefront options, which are lightweight and corrosion resistant.
Don’t get confused! Galvannealed vs Galvanized Steel
Galvannealing and galvanizing both describe a treatment process for carbon steel. They have a lot in common, but the differences in the processes and the final results are key.
The Galvanizing Process
The galvanizing process uses carbon steel and a hot dip process. First, the surface of the carbon steel is prepared in three steps. It’s degreased, which removes dirt and oils. Then, it goes through a chemical cleaning to remove any rust. Finally, it goes through fluxing which removes any remaining oxides and leaves behind a protective layer to prevent further oxides from forming.
Once the carbon steel is dry, it is completely immersed in a molten zinc bath, which is kept at around 842ºF. While in the bath, the zinc reacts with the iron in the steel to form a bonded zinc-iron layer.
When the carbon steel is removed from the bath, the excess zinc is drained away, leaving behind the zinc-iron bonding layer which adheres a pure zinc layer to the steel underneath.
The Galvannealing Process
The galvannealing process is very similar to the galvanizing process. It starts the same way, with preparing the surface of the steel and fully immersing it in a molten zinc bath, but the galvannealing process takes an additional step before the metal is ready to be inspected for quality.
Immediately after being withdrawn from the zinc bath, while the zinc is still molten, the steel enters an annealing furnace which heats the metal to a range, somewhere between 900–1000ºF for a few seconds. This additional step results in a reaction which causes the iron in the steel and the zinc to migrate toward each other and creates a zinc-iron coating. In comparison, the galvanized steel coating is pure zinc with a bonding layer between the zinc and the steel.
So, what’s actually the difference?
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The zinc coating on galvanized steel is weaker and more brittle than the zinc-iron coating on galvannealed steel
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The zinc-iron coating allows for better paint adherence
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Pre-treatment for painting is not required for galvannealed steel (most steel doors, including CDF’s, are delivered primed and ready to paint)
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Galvannealed steel is easier to weld than galvanized steel
Our Doors Use Galvannealed Steel
We use 18-gauge galvannealed steel to craft our hollow metal doors for its many fantastic benefits:
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Durability: Galvannealed steel is durable and corrosion resistant.
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Fire Rating: There are other metals, like aluminum, which can’t be fire rated.
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Longevity: With proper maintenance, a hollow metal door made with galvannealed steel can last for 30 years or more.
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In-field repair: Doors made with softer metals like aluminum can’t be repaired if they get dented, but steel doors can.
Did you know there are different gauges of metal that can be used to manufacture doors? CDF’s standard is 18-gauge steel for doors with a 16-gauge steel door frame, but there are custom options available from 20 gauge (the thinnest) all the way up to 12 gauge (the thickest).
Why Our Metal Doors Have to Be Painted
Above, it was mentioned that galvannealed steel doors don’t need any surface preparation before being painted, and while true, a proper primer will help keep your door in top condition for years or decades by helping to smooth the surface before paint is applied. That’s why CDF Distributors’ steel doors are delivered primed and ready to paint.
Painting your metal doors and frames is an important step in the process to ensure your doors stay in good condition without the need for repair or replacement. It helps to protect the zinc-iron coating from scratches or damage that could introduce moisture and produce rust.
Painting metal doors is also an aesthetic choice. If you’re replacing doors in an elementary school, for example, you could choose a color to represent classrooms and another color for restrooms or janitorial closets to help young students and school visitors navigate hallways.
