It should be noted that the primary aim of hot-dip galvanizing is to provide anti-corrosion protection and, to a lesser extent, a decorative coating. To get an aesthetically nicer looking surface galvanized surfaces are usually painted, which also increases the products lifespan.
The painting of galvanized surfaces has some distinctive traits due to the low coarseness of the surface and the chemical compounds that form on the zinc coating. This requires thorough preparation of the zinc surface before painting. Both mechanical and chemical prepping methods are used. The most common method is a light treatment through sandblasting, but this requires extreme caution, and the following instructions should be considered. The most suitable powerwashing media is natural sand or aluminium oxide (under no circumstances should steel shot be used). The grain size of the material should be 0.2-0-5 mm, the air pressure 0.2-0.3 MPa, powerwash distance at least 500 mm, and the angle 30-60 degrees. The zinc will peel off the metal surface if the pressure is too high, the grain size too big, the blasting angle perpendicular, and the distance too close.
Chemical cleaning of different galvanized surfaces.
- Pure galvanized surface â€“ washing with an ammonia solution and then powerwash, washing with different washing solutions (phosphates etc.) from paint producers according to the instructions of the producer
- Dirty, smeared surfaces â€“ same treatment, increase the concentration of the solution when necessary, brushless
- White rust (mould) covered surfaces â€“ washing with a vinegar solution and then powerwash, washing with different washing solutions from paint producers according to the instructions of the producer, sandblasting with fine grain sand
Choosing the paint:
Not all paints are suitable for a galvanized surface. Nowadays, all manufacturers of industrial paints have their own recommended paint types for galvanized surfaces, and the manufacturerâ€™s instructions and requirements should be followed during use. Dual component paints are the most common type of paints for hot-dip galvanized surfaces. In practice, epoxy paint is used for the first layer and the first layer should be relatively thin (the paint should be heavily diluted to speed up the removal of gasses from the paint layer). When necessary experience in the painting of galvanized surfaces is lacking, paint producers should be consulted and asked for instructions.