Corrosion protection decides how long a metal fabrication lasts. A well-welded railing that is painted wrongly will rust within two or three years. Below are the differences between the two methods we use most often, and when each one suits.
How powder coating works
The paint is a powder. The gun charges it electrostatically, and the earthed part attracts it and is covered evenly, including edges and corners. The part then goes into an oven, where the powder melts and cures, usually at 180–200 °C.
Advantages:
- an even coat, usually 60–120 µm in a single pass
- good resistance to scratches and knocks
- no solvents
- any RAL colour, matt, satin or gloss
- the part is ready as soon as it has cooled
Limits:
- the part has to fit in the booth and the oven
- touch-ups on site are done with wet paint, so they do not look as good
- galvanised steel needs special surface preparation, otherwise blisters can appear
How wet painting works
The paint is applied in several coats: primer, sometimes an intermediate coat, then the topcoat. The total thickness and the type of paint are chosen according to the environment the structure sits in. The standard used for this is ISO 12944, which divides environments into corrosivity categories, from C1 (dry interior) to C5 and CX (aggressive industrial, marine).
Advantages:
- no size limit: beams, trusses and whole structures can be painted
- it can also be applied on site
- touch-ups after installation blend in well
- systems exist for very aggressive environments
Limits:
- it takes longer, because each coat has to dry
- quality depends heavily on surface preparation and on the conditions during application (temperature, humidity)
Surface preparation matters more than the paint
Whichever method is used, paint only holds on a clean surface. For structures with demanding requirements, the surface is blasted to grade Sa 2½ (to ISO 8501-1): clean metal, free of rust and mill scale. Expensive paint on an unprepared surface will flake off anyway.
What we recommend, in short
- Railings, parapets, interior stairs: powder coating
- Gratings, housings, small and medium parts: powder coating
- Large structures (beams, columns, trusses): wet paint
- Elements welded on site: wet paint, with touch-up after installation
- Exterior, damp or aggressive environment: galvanising + paint (duplex system)
What to tell us so we choose correctly
- where the part will be: interior, exterior, near the sea, in a hall with chemicals
- what finish you want: RAL colour, gloss level
- whether the part will still be welded or cut on site
- what service life the project requires
We do both in our workshop. See the details on the metal fabrication and steel structures page, and our other services.