Steel Powder Coating (RAL Colours)

Powder types and where each is used

Polyester powders are the general-purpose choice: good UV resistance, good flexibility, cured at 180-200 °C for 10-15 minutes. Epoxy powders have the best chemical and corrosion resistance and edge coverage but chalk within months under desert sun, so they are limited to indoor panels and to primer layers. Epoxy-polyester hybrids sit between the two and are the usual indoor finish for enclosures and furniture. Super-durable polyesters, qualified to Qualicoat class 2 or equivalent, keep gloss and colour 2 to 3 times longer than standard polyester and are the correct choice for facades, signage and solar structures in Riyadh, Dubai and Upper Egypt.

Pretreatment decides how long the coating lasts

Powder does not adhere to mill scale, laser oxide or oil. Every part is degreased, then either shot blasted to Sa 2.5 or chemically converted. Iron phosphate is the low-cost pretreatment for indoor parts; zinc phosphate roughly doubles salt spray resistance and is the minimum for outdoor use in the UAE and Saudi Arabia. Blasting to Sa 2.5 with a 40-70 µm profile gives the best adhesion on hot-rolled S235JR plate and welded frames and removes the dark oxide left by oxygen-assist laser cutting on edges, which otherwise flakes off with the coating within a year.

For hot-dip galvanised steel a sweep blast or specific etch is needed before powder; without it the coating peels in sheets. Duplex systems (galvanising plus powder) are common for solar structures and highway signage and give 20+ years in dry inland conditions.

RAL colours, gloss and texture

Around 30 RAL colours are stocked by most coating shops in the region: RAL 9010 pure white, 9016 traffic white, 7035 light grey, 7016 anthracite, 9005 jet black, 5010 gentian blue, 3020 traffic red, 1023 traffic yellow, 6005 moss green and 8017 chocolate brown are the usual ones. Any other RAL Classic colour is available with 3 to 7 working days added for powder supply and a minimum batch of about 20 kg of powder, which covers roughly 80 to 100 m² of surface. RAL Design and Pantone matches, metallics and two-coat effects are possible but need a larger minimum.

Gloss is specified at 60°: full gloss 80-90 GU, satin 30-60 GU, matt below 30 GU. Fine and coarse texture finishes hide weld grinding marks and light scratches and are preferred for machine guards, electrical cabinets and outdoor furniture. Colour tolerance is Delta E below 1.5 against the RAL reference; two batches from different powder lots may differ by up to Delta E 1, so order matching parts together.

• Stocked colours: usually no surcharge, 3-5 working days
• Non-stocked RAL Classic: 3-7 working days added, 20 kg minimum powder
• Textured or structured finish: hides defects, adds 10-15%
• Metallic and bonded effects: 15-30% surcharge, single-source the batch
• Clear coat over metallic: second pass, adds 20-30%

Designing steel parts for powder coating

The Faraday cage effect means powder does not reach deep into narrow channels and recesses: a slot narrower than 5 times its depth will have thin coating at the bottom. Sharp laser-cut edges pull the coating thin, so a 0.5 mm edge break or deburring improves edge coverage significantly. Closed sections trap pretreatment chemicals and cure gases; add 6-10 mm drain holes at low points and vent holes in tubes. Threads, bearing seats and earthing points must be masked or re-tapped afterwards. Every part needs a hanging point: a 6 mm hole in a hidden position saves a visible hook mark.

Welded assemblies should be fully welded, not stitch welded, where they are exposed outdoors; the gap in a stitch weld collects moisture under the coating and starts rust that lifts the film. Grind welds flush only where the surface is visible; a textured finish covers the rest.

Performance in heat, dust and salt air

Powder coating on steel is stable to 120 °C continuous, which covers dark panels reaching 80-90 °C in direct sun in Riyadh or Aswan. Sand abrasion at ground level, for example on solar structure legs and gate bottoms, wears standard polyester at 5-10 µm per year; specify 100-120 µm film or a textured super-durable powder for those zones. Within 5 km of the coast in Alexandria, Jeddah, Dammam and the UAE, a zinc-rich primer under the polyester or a duplex galvanised system is the difference between 3 and 15 years before visible rust at edges.

Applications

Pricing and lead time

Powder coating cost is driven by the surface area to be coated and the part size, since large parts fill the oven and the hanging line; by the pretreatment system, where blasting and zinc primer cost 1.5 to 2.2 times a simple phosphate; and by colour and finish, since non-stock RAL, textures and metallics add powder minimums and surcharges. Quantity reduces the cost per part sharply because line setup and colour change are fixed. Coating adds 2 to 4 working days to a cutting and bending order for stocked colours and 5 to 9 working days for special colours or primer systems, giving a total of 6 to 12 working days from file to delivery.

Frequently asked questions