Galvanised steel starts to rust wherever the zinc coating is broken: at scratches, cut ends, drilled holes and worn patches. The fix is to clean the damaged area and apply a zinc-rich touch-up. For scratches and worn coatings, Micron 2200 Zinc Aluminium Touch Up Paint is an aerosol whose page lists fences, railings, pipelines and galvanised structures. For cut edges, drilled holes or large areas brushed on site, use Micron 2218 MetArmor Z, a brushable 5 L zinc-rich paint.
Why it happens
- Cutting or drilling after galvanising. Every cut end and hole exposes bare steel.
- Handling and transport damage. Chains, slings and stacking scrape through the zinc.
- Weathering. Over years, the zinc layer thins, especially on edges and in wet spots.
You will see rust starting at cut ends or scratches, and bare steel showing through the galvanising.
How to fix it
Choose by the damage and the job size:
- Scratches and worn coatings, aerosol convenience: Micron 2200 Zinc Aluminium Touch Up Paint. Its page says it forms a sacrificial zinc layer and is for repairing scratches and worn-out coatings, and lists galvanised steel structures, pipelines, fences, railings and outdoor fixtures.
- Cut edges or drilled holes: Micron 2218 MetArmor Z Paint. Its page lists repair of weld joints, scratches or cut edges.
- Large areas or many structures, brushed on site: Micron 2218, 5 L, which its page describes as easy to apply on site without spray equipment. It lists scaffolding, metal railings, pipes and tanks.
Preparation, from the 2218 page:
- Remove rust, grease, oil, dust and old paint.
- Use wire brushing, sandpaper or blasting to help the coating adhere.
- Make sure the surface is dry.
- Stir 2218 thoroughly before and during use and brush on in even strokes.
Follow the coats and drying times given on the 2218 TDS. Work the paint well into the cut face and the edges of holes, since these are the areas with no zinc at all. The 2200 page has no step-by-step directions, so follow the instructions on the can and the TDS, with the same cleaning first.
What to avoid
- Clean off rust, grease and loose paint before touch-up. Coating over rust traps it.
- Do not paint in rain or on a wet surface.
- Clean 2218 tools only with the solvents its page names (toluene, xylene or lacquer thinner), with ventilation and away from flames.
- Do not use touch-up paint as a substitute for repair where the steel itself is badly corroded.
When to ask an expert
Talk to a structural or corrosion engineer if:
- corrosion is extensive or a structural member has lost section;
- the structure is load-bearing and you are not sure it is still sound.
Ask Micron technical if the job has a coating specification, such as a required zinc content or film thickness.
FAQ
Why do cut ends rust first?
Cutting after galvanising leaves the cut face as bare steel with no zinc on it. Edges also hold water and see more wear.
Should I use spray or brush on railings?
For a few scratches, the 2200 aerosol is quick. For cut edges, many railings, or site work without spray equipment, the brushable 2218 is the practical choice.
Does the touch-up match galvanised steel?
The 2200 page says it matches existing galvanised coatings; the 2218 page says it dries to a silver-grey metallic finish that visually matches galvanised surfaces.
Can I paint over the zinc touch-up later?
The 2218 page says it also serves as an intermediate primer coat in multi-layer systems. Topcoat compatibility is not stated, so check your topcoat with Micron.
See the product: Micron 2200 Zinc Aluminium Touch Up Paint. Related: 2218 MetArmor Z Paint. More welding and fabrication fixes: welding hub.