Short answer: National Zinc Chromate Primer is an alkyd-based anti-corrosive primer for both ferrous and non-ferrous metals: steel, galvanised steel, aluminium and brass. On galvanised steel or aluminium, degrease and sand the surface, apply an etch (wash) primer, then one coat of Zinc Chromate, Synthetic Undercoat and enamel; National’s specifier puts that system at 140 to 150 microns in total. It covers about 14 to 19 m² per litre and recoats after 12 hours at 30°C.
Why galvanised and aluminium need a different primer
National’s surface preparation guide says galvanised steel and aluminium are difficult to paint because of adhesion problems: galvanising is very smooth. Its answer is to degrease, sand, and apply an etch primer, which leaves a tacky surface the next coat can grip. Zinc Chromate is the only one of National’s four alkyd metal primers that its data sheet lists for non-ferrous metals:
| Primer | National lists it for | m² per litre | Recoat at 30°C | Flash point |
|---|---|---|---|---|
| Zinc Chromate | Steel, galvanised steel, aluminium, brass | 14 to 19 | 12 h | 32°C |
| Red Oxide | Steel, domestic and mildly corrosive | 14 to 18.5 | 8 to 12 h | 38°C |
| Red Lead | Steel structures, mild to moderately corrosive | 13 to 17.5 | 12 h | 38°C |
| Zinc Phosphate | Structural steel, tanks, pipelines, moderately corrosive | 11.5 | 10 h | 38°C |
Key facts
| Decorative sheet | Protective sheet | |
|---|---|---|
| Type | Alkyd anti-corrosive primer with zinc chromate pigment, single pack, matt | |
| Colours | Yellow, yellowish green | |
| Volume solids | 57 ± 2% | 52 ± 2% |
| Spreading rate | 14 to 19 m² per litre | 13 to 17 m² per litre |
| Film per coat | 30 to 40 µm dry (50 to 70 wet) | 30 to 40 µm dry (55 to 75 wet) |
| Drying at 30°C | Touch 4 to 5 h; recoat 12 h; hard 24 h | Touch 4 h; recoat 12 h; hard 24 h |
| Application | Brush, roller or spray (airless 2100 psi, tip 0.015 to 0.020 inch; air 50 psi) | |
| Thinning | 5 to 15% | Airless 5 to 10%, air 10 to 15%, brush 10% |
| Thinner | National G.P. Thinner | |
| Flash point | 32°C | |
| Shelf life | 18 months, sealed | |
Step 1: prepare the metal
| Metal | National’s preparation |
|---|---|
| Galvanised steel, aluminium | Degrease. Sand with abrasive paper and solvent. Surface clean and dry. Apply an etch (wash) primer before the system. |
| Steel | Degrease, then clean to St 2 by hand or power tool, or blast to Sa 2.5. Surface clean and dry. |
Degreasing comes first in every case: a solvent wash wiped dry with clean rags, or detergent rinsed off with fresh water. Sanding a greasy surface only spreads the contamination.
Step 2: apply the system
| Coat | Galvanised / non-ferrous (specifier) | Steel (data sheet) |
|---|---|---|
| Etch | Wash Primer, 1 × 5 to 8 µm | Not used |
| Primer | Zinc Chromate, 1 × 50 µm | Zinc Chromate, 1 × 40 µm |
| Undercoat | Synthetic Undercoat, 1 × 40 to 50 µm | Synthetic Undercoat, 1 × 40 µm |
| Finish | Gloss I or Gloss II, 1 × 40 µm | Gloss I or II, 1 to 2 × 35 µm |
| Total | 140 to 150 µm | About 115 to 150 µm |
Ask us for National’s wash primer when you order; it is part of the galvanised system and is not covered by the Zinc Chromate data sheet.
What the data sheet numbers mean
- Coverage = volume solids × 10 ÷ dry film: 570 ÷ 30 = 19 m² per litre, 570 ÷ 40 ≈ 14.3. The specifier’s 50-micron galvanised coat works out at about 11.4 m² per litre.
- Wet film = dry film ÷ volume solids: 50 ÷ 0.57 ≈ 88 microns wet for the galvanised system’s primer coat.
How much to buy
| Area | At 40 µm (steel) | At 50 µm (galvanised system) |
|---|---|---|
| 25 m² | 1.3 to 1.8 L | about 2.2 L |
| 50 m² | 2.6 to 3.6 L | about 4.4 L |
| 100 m² | 5.3 to 7.1 L | about 8.8 L |
Mistakes to avoid
- Skipping the etch step on new galvanising. National’s guide calls for an etch primer on galvanised metal.
- Sanding before degreasing. Degrease first.
- Storing it hot. Its flash point is 32°C, lower than National’s other alkyd primers. Keep it shaded and away from flames.
- Leaving it exposed. It is a primer; finish with undercoat and enamel.
Frequently asked questions
Can I use it on plain steel too?
Yes, National lists steel along with non-ferrous metals. On mixed jobs (steel frames with galvanised infill, for example) one primer covers both.
Can I paint emulsion over it?
National’s systems put Synthetic Undercoat and alkyd enamel over it. The data sheet says it can be overcoated with National enamel paints.
Which thinner?
National G.P. Thinner. See which National thinner to use and our guide to painting galvanised metal.
Buy in Sharjah and Dubai
Al Tashteb Al Saree is an authorised National Paints retailer in Bu-Tina, Sharjah. Message us on WhatsApp for Zinc Chromate, wash primer, undercoat and enamel, or see all National Paints products.
Sources
- National Zinc Chromate Primer, decorative data sheet (PDF)
- National Zinc Chromate Primer, protective data sheet (PDF)
- National Paints surface preparation guide, Sec. A-2 (PDF)
- National Paints systems specifier (PDF)
All via AEC Online, retrieved 4 November 2026. Quantities are our own calculations. The main image is illustrative.
