Galvanised steel requires special surface preparation prior to painting. The steel has been treated with a special zinc coating to reduce rust. This coating must be properly cleaned and roughened for the best adherence of the primer prior to painting. A well-done paint job on galvanised steel will last a long time without peeling or flaking. The additional protection offered by the paint also should help prolong the life of the piece by staving off rust and corrosion.
Wash the galvanised steel with hot soapy water and rinse with hot water. Allow it to dry thoroughly.
Make a solution of 1 to 2 per cent ammonia with water by mixing equal parts of water and ammonia. Household ammonia is approximately 5 to 10 per cent ammonia so cutting the amount of ammonia in half should yield a solution that is strong enough to prepare the zinc for painting. Rinse with hot water and allow it to dry completely.
Use 240 grit sandpaper and sand the entire surface. If there are handles or parts that can be removed, remove them and sand each part separately. If the part cannot be removed because it is welded or riveted to the main piece, be sure to get the sandpaper into every crevice as well as you can.
Wipe the entire piece down with a tack cloth. A tack cloth is available in the painting section of most hardware stores. It is a cloth that has a sticky substance built in to pick up all the fine sanding dust to prepare surfaces for painting.
Spray metal primer over the entire surface. Work in smooth strokes from top to bottom to avoid runs, sags and drips. Allow it to dry completely according to the recommended drying time printed on the primer can label.
Inspect for runs, drips or sags. If needed, sand any imperfections and apply a coat of primer to the area.
Spray the entire surface with metal paint of the same brand as the primer. Each brand of primer and paint are formulated to work best together. Work in smooth strokes from top to bottom to avoid runs, sages and drips. Allow it to dry completely according to the recommended drying time printed on the paint can label.
Inspect for runs, drips or sags. If needed, sand any imperfections and apply a coat of paint to the area.
Keep the spray can moving while applying primer and paint to avoid drips, runs and sags.
Work in a well-ventilated area while painting. Do not inhale paint fumes. Read and follow all recommended precautions that are printed on the primer and paint can labels.