When paint on steel fabrication fails and rust creeps underneath, the usual gap is a sacrificial zinc-rich base layer and proper surface preparation. Micron 2218 MetArmor Z Paint is a brushable zinc-rich coating whose page says it serves as an intermediate primer coat in multi-layer protective systems and lists use as a base primer for heavy-duty anti-corrosion coating systems. Check compatibility with your topcoat before you start.
Why it happens
- Edges, welds and corners. Paint pulls thin over sharp edges and weld beads, so these are where rust usually starts first.
- No sacrificial base layer. A topcoat alone is a barrier. Once it is scratched or chipped, rust spreads under it. A zinc-rich layer corrodes in place of the steel and slows that creep.
- Poor surface preparation. Paint applied over mill scale, rust, oil or dust has nothing sound to hold onto and lifts early.
You will see the topcoat failing, rust creeping from scratches and edges, and a need for a galvanic base under paint on tanks, pipes, railings or fabricated structures.
How to fix it
Use a zinc-rich primer under your topcoat, on a properly prepared surface.
- Zinc-rich primer, brushed: Micron 2218 MetArmor Z Paint, 5 L. Its page describes a high zinc content that offers cathodic protection and lists base primer for heavy-duty anti-corrosion coating systems, pipes and tanks, scaffolding and railings, industrial enclosures and marine equipment.
From the 2218 page:
- Prepare the surface. Clean thoroughly to remove rust, grease, oil, dust and old paint. Use wire brushing, sandpaper or blasting to help the coating adhere. The surface must be dry and free from contaminants.
- Mix. Stir thoroughly before and during use so the zinc particles stay evenly dispersed.
- Apply. Brush on in even strokes.
- Dry. Follow the coats and drying times on the 2218 TDS (it states touch dry, handle dry and full cure at 25°C and 50% RH) before applying the topcoat.
Pay extra attention to weld seams, edges and corners when brushing. These are the spots where paint is thinnest and where rust usually starts, so make sure the primer covers them fully. If parts are already galvanised and only damaged areas need priming, the 2218 page also lists touch-up of galvanised steel structures and repair of weld joints, scratches or cut edges.
What to avoid
- Do not apply over rust, grease, dust or old paint. The page is explicit that the surface must be clean and dry.
- Clean tools with toluene, xylene or lacquer thinner only, as stated on the page, and keep those solvents away from sparks and flames, with ventilation.
- Do not let the zinc settle in the tin while you work. Stir during use.
- Do not assume any topcoat will go over it. The page does not list compatible topcoats.
When to ask an expert
Hand off to Micron technical if:
- you need compatibility with a specific topcoat system;
- the job has a coating specification, such as a dry film thickness, zinc content or a standard;
- the structure is in a marine or chemical environment with a design life to meet.
FAQ
What does a zinc-rich primer do that normal primer does not?
The zinc corrodes in place of the steel where the coating is damaged. The 2218 page calls this cathodic protection, preventing rust beneath the coating.
Can I topcoat over 2218?
The page says it serves as an intermediate primer coat in multi-layer systems, but it does not list compatible topcoats. Check your topcoat with Micron before you commit a job.
Can I weld through it?
The page mentions post-cure weld-through compatibility "for certain applications" only. Ask Micron about your specific case before welding over it.
Is it a spray or brush product?
2218 is brushable and supplied in 5 L. Its page says it can be applied on site without spray equipment.
See the product: Micron 2218 MetArmor Z Paint. More welding and fabrication fixes: welding hub.