Metal door frames are typically made out of steel, and must be painted to protect them from weather-related corrosion.
If possible, paint the door frame before installation to reduce the amount of masking required to protect surrounding surfaces. Touch up any marks or scratched caused during installation.
As with any painting project, surface preparation and cleaning is the key to a quality job. Spending extra time removing any rust or loose paint will significantly extend the life of the paint.
Remove the door by pulling the hinge pins. This can be accomplished by driving a screwdriver underneath the tops of the hinge pins.
Remove any strike plates and latch hardware from the door frame.
Remove any surface rust or loose paint with a wire brush. Existing paint may be left in place if it adheres well to the door frame, but remove any paint that appears loose, has bubbles or easily chips or flakes.
Remove and replace any caulking or sealant around the door frame that appears loose or dried out.
Choose a high quality primer and paint.
Paint is available in either water or oil base. Oil base paints are more difficult to apply and clean up, but are generally considered to be longer lasting.
Paints are also available in gloss and matt finishes. Choose a finish based on your decorative preference.
Procure a paint brush appropriate for the chosen paint. Use good quality brushes for the best finish. A two inch sash brush is a good choice for door frames.
Mask all surrounding areas with painter's tape.
Clean all metal surfaces with a rag soaked in mineral spirits. This will remove any surface oils and dirt.
Apply primer to all bare metal and any areas where rust has been sanded. If painting over a previous coat of paint, consider applying primer to the entire door frame.
Apply a finish coat. Start at the top and work to the bottom. Brush paint evenly, and lightly brush painted areas with a dry brush to remove streaks and runs. Apply multiple thin coats rather than one thick coat.
Reinstall any strike plates or hardware previously removed. Reinstall the door by inserting the pins into the hinges.
Choose paint and primers from the same manufacturers to assure compatibility.
Always wear eye protection when using a wire brush and working with mineral spirits.