Short answer: National Red Oxide Primer is a general-purpose, alkyd-based anti-corrosive primer for steel in domestic and mildly corrosive environments, such as gates, grilles, railings, light frames and indoor steelwork. Prepare the steel by degreasing it, then cleaning it by hand or power tool to St 2 or blasting to Sa 2.5. Apply one coat at 30 to 40 microns dry. It covers about 14 to 18.5 m² per litre and is ready for Synthetic Undercoat after 8 to 12 hours at 30°C. Thin it with National G.P. Thinner.
When to use Red Oxide Primer
National positions Red Oxide as its everyday steel primer: good adhesion, flexibility and durability, overcoated with National alkyd enamels. Its data sheet limits it to domestic and mildly corrosive environments. Pick a different National primer when the job is harsher or the metal is not plain steel:
| Primer | National lists it for | Colour | m² per litre | Recoat at 30°C |
|---|---|---|---|---|
| Red Oxide | Steel, domestic and mildly corrosive | Red | 14 to 18.5 | 8 to 12 h |
| Red Lead | Steel structures, mild to moderately corrosive | Red-orange | 13 to 17.5 | 12 h |
| Zinc Phosphate | Structural steel, tanks, pipelines, moderately corrosive | Grey | 11.5 | 10 h |
| Zinc Chromate | Steel, galvanised steel, aluminium, brass | Yellow / yellowish green | 14 to 19 | 12 h |
Key facts
| Decorative sheet | Protective sheet | |
|---|---|---|
| Type | Alkyd anti-corrosive primer, single pack, matt red | |
| Volume solids | 56 ± 2% | 53 ± 2% |
| Spreading rate | 14 to 18.5 m² per litre | 13 to 17 m² per litre |
| Film per coat | 30 to 40 microns dry (55 to 70 or 75 wet) | |
| Drying at 30°C | Touch 1 to 2 h; recoat 8 to 12 h; hard 24 h | Touch 4 h; recoat 12 h; hard 24 h |
| Application | Brush, roller or spray (airless 2200 psi, tip 0.015 to 0.020 inch; air 50 psi) | |
| Thinning | 5 to 15% | Airless 5 to 10%, air spray 10 to 15%, brush 10% |
| Thinner | National G.P. Thinner | |
| Flash point | 38°C | |
| Shelf life | 18 months, sealed | |
Step 1: prepare the steel
National’s surface preparation guide calls preparation “the single important factor” in how a paint system performs. For steel it sets out this order:
- Degrease first. Wash with solvent and wipe dry with clean rags, or use a detergent solution followed by fresh-water hosing so no detergent is left behind. Cleaning before degreasing spreads oil around.
- Remove rust and mill scale. National’s two standard specifications are Sa 2.5, a very thorough blast close to white metal, and St 2, hand or power tool cleaning. The guide notes that power tools (St 3) cannot remove tightly adhering mill scale; only blasting does.
- Prime while the surface is clean and dry. Freshly cleaned steel starts to re-rust, so do not leave it bare.
| Swedish standard | What it means | BS 4232 | SSPC |
|---|---|---|---|
| Sa 3 | Blast to visually clean steel | First Quality (100% bare metal) | SP-5 |
| Sa 2.5 | Very thorough blast, near white | Second Quality (at least 95%) | SP-10 |
| Sa 2 | Commercial blast | Third Quality (at least 80%) | SP-6 |
| Sa 1 | Light blast | None | SP-7 |
| St 2 / St 3 | Hand or power tool cleaning | For less demanding work | |
The same guide grades the starting condition of steel from A (mill scale with little rust) to D (general visible pitting). The further along that scale, the more the job needs blasting rather than wire brushing.
Step 2: apply the system
- Red Oxide Primer, one coat at about 40 microns dry.
- National Synthetic Undercoat, one coat at about 40 microns, after 8 to 12 hours.
- National Synthetic Enamel Gloss I or II, one to two coats at about 35 microns each.
National also lists Red Oxide as the primer under Flat/Matt Enamel, Eco Enamel, Industrial Quick Drying Enamel (straight over primer, no undercoat), Camouflage Enamel and Aluminium Paint.
How much to buy
| Steel area | Red Oxide, 1 coat | Undercoat, 1 coat | Gloss II, 2 coats |
|---|---|---|---|
| 25 m² (a large gate, both sides) | 1.4 to 1.8 L | 1.5 to 1.9 L | 3 to 4 L |
| 50 m² | 2.7 to 3.6 L | 2.9 to 3.8 L | 6.1 to 8 L |
| 100 m² | 5.4 to 7.1 L | 5.9 to 7.7 L | 12.1 to 16 L |
Heavier systems in National’s specifier
The data sheet’s three-coat system suits domestic work. National’s systems specifier sets out two thicker Red Oxide systems for structural steel, referenced to BS 5493:
| Exposure | Red Oxide Primer | Synthetic Undercoat | Gloss I or II | Total dry film |
|---|---|---|---|---|
| Non-polluted air (BS 5493 Table 4F, SF 7) | 2 × 35 µm | 2 × 35 to 40 µm | 1 × 25 to 40 µm | 165 to 190 µm |
| Polluted air (BS 5493 Table 4F, SF 8) | 2 × 35 µm | 2 × 35 to 40 µm | 2 × 25 to 40 µm | 190 to 230 µm |
What the data sheet numbers mean
- Coverage = volume solids × 10 ÷ dry film. At 56% solids: 560 ÷ 30 = 18.7 m² per litre and 560 ÷ 40 = 14 m² per litre, which is the range on the sheet.
- Wet film to aim for = dry film ÷ volume solids. For 35 microns dry: 35 ÷ 0.56 ≈ 63 microns wet. Check it with a wet-film comb as you go.
- Thinner adds no solids, so a thinned coat needs a thicker wet film to reach the same dry thickness.
Our own calculations. Theoretical figures assume no losses.
Frequently asked questions
Can I use Red Oxide on galvanised steel or aluminium?
National does not list it for those. Its surface guide says galvanised steel and aluminium need degreasing and an etch primer because adhesion is poor; its data sheets name Zinc Chromate Primer for galvanised steel and aluminium. See painting galvanised metal.
Is Red Oxide enough for coastal or industrial sites?
Its data sheet stops at mildly corrosive environments. For moderately corrosive conditions, National lists Zinc Phosphate or Red Lead; for heavy duty, see the epoxy systems in our steel painting guide.
Can I put emulsion over it?
National’s system puts Synthetic Undercoat on top, and the undercoat’s data sheet says it can be overcoated with National alkyd finishes or emulsion paints.
Which thinner and how much?
National G.P. Thinner: about 10% for brushing, 5 to 10% for airless spray and 10 to 15% for conventional spray, according to the protective data sheet. See which National thinner to use.
Is it flammable?
The flash point is 38°C. Store it sealed and out of direct sun, ventilate when applying, and read the product safety data sheet.
Buy in Sharjah and Dubai
Al Tashteb Al Saree is an authorised National Paints retailer in Bu-Tina, Sharjah. We stock primers, undercoat, enamels and G.P. Thinner for complete steel systems. Send us your steel area on WhatsApp and we will price the full system, or see all National Paints products.
Sources
- National Red Oxide Primer, decorative data sheet (PDF)
- National Red Oxide Primer, protective coatings data sheet (PDF)
- National Paints surface preparation guide, Sec. A-2 (PDF)
- National Synthetic Undercoat data sheet (PDF)
- National Paints systems specifier (PDF)
- National Synthetic Enamel Gloss II data sheet (PDF)
All via AEC Online, retrieved 4 November 2026. Quantities are our own calculations. The main image is illustrative.
