The finish on metalwork is not decoration. It is the thing standing between the steel and the weather, and it decides whether a gate looks tired in three years or twenty. It is also the easiest place for a quote to be quietly cheapened, because the difference is invisible on handover day.
Paint: primer and enamel
The default on mild steel fabrication. A coat of red oxide primer and one or two of synthetic enamel, usually brushed or sprayed at the workshop or on site.
It is cheap, it can be touched up by anyone, and it is entirely reasonable for interior work or anything under cover. Outdoors it is the weakest of the options: expect to repaint every two to four years depending on exposure, and understand that repainting a fitted gate means masking, weather windows and downtime.
If you do choose paint for an exterior item, the primer matters more than the top coat. A zinc-rich or epoxy primer under the enamel buys years over plain red oxide for a small addition to the cost.
Powder coating
A dry polyester or epoxy powder applied electrostatically and baked in an oven, giving a hard, even film typically 50–80 microns thick. The standard good finish for aluminium windows, gates, grills and railings.
What to ask about:
- Thickness in microns. This is the number that predicts durability. A thin coat on a cheap job will chalk and fade.
- Pre-treatment. Powder sticks to what it is sprayed on. If the metal was not degreased and chemically treated first, the coating will lift in patches regardless of how thick it is. Pre-treatment is invisible and is the first thing skipped.
- Interior or exterior grade. Polyester powders are formulated for UV exposure; some cheaper epoxy powders are not and will chalk badly in direct sun.
Powder coating's weakness is repair. A deep scratch to bare metal cannot be re-powdered in place, only touched up with paint that will never quite match.
Anodising
For aluminium only. An electrochemical process that grows a hard oxide layer out of the metal itself rather than laying something on top of it. Because the finish is the surface, it cannot peel or flake.
It is extremely durable, holds up well to sun, and suits natural metallic finishes. The trade-offs are a narrower colour range than powder coating and a sensitivity to cement and alkaline cleaners — splashes of mortar left on anodised sections during construction can stain them permanently. Protect anodised frames until building work nearby is finished.
Hot-dip galvanising
Steel dipped in molten zinc, which metallurgically bonds to the surface and then corrodes sacrificially in place of the steel beneath. For exterior structural work — sheds, staircases, railings, gates in harsh conditions — nothing else in common use lasts as long.
It is not a decorative finish: the surface is a matt grey with a visible crystalline pattern. It can be powder coated over for appearance, which gives the best of both and costs accordingly. Practical constraints: items must fit the galvanising bath, there is a lead time, and the design must allow zinc to drain, so hollow sections need vent holes that the fabricator should plan from the start rather than drill as an afterthought.
Choosing, in one paragraph
Indoors or under cover, paint is fine. Outdoors and visible — windows, gates, railings — powder coating over proper pre-treatment is the sensible default, with anodising a strong alternative on aluminium. Outdoors and structural, or anywhere near the coast, hot-dip galvanising is worth the premium and will likely outlast the rest of the installation.
The coastal exception
Salt air changes every one of these answers. Within a few kilometres of the sea, ordinary powder-coated mild steel will show rust bleeding at the edges and fixings within a couple of seasons. There the real choices narrow to galvanised-and-powder-coated steel, aluminium, or stainless of grade 316. Paying for grade 304 near the sea is a common and expensive mistake — it is 316 that contains the molybdenum that resists chloride.