Start with the asset and exposure

Document whether the steel is new carbon steel, previously painted, galvanised or another metal; whether the work is shop-applied or field-applied; and whether the asset is accessible for future repair. Identify rain, condensation, salt deposition, process contaminants, abrasion, temperature and direct sunlight. Atmospheric exposure, splash and tidal exposure, immersion and chemical containment are separate service conditions. A system proposed for exposed building steel should never be assumed suitable inside a tank or below water.

ISO 12944-2 provides a framework for classifying environments. ISO 12944-5 addresses paint-system selection for specified environments and preparation grades. Neither standard awards an ISO category or durability classification to an ALKA system merely because it contains zinc, epoxy or polyurethane. The project specification must state its environment, intended durability, preparation and evidence requirements.

What the preparation specification must cover

Clean before and after abrasive work

Remove oil and grease by an approved method before abrasive blasting; abrasive impact can spread contamination rather than eliminate it. Blasting then removes rust and scale and creates a profile suited to the selected primer. Specify an actual preparation grade, rather than the vague instruction “blast clean.” ISO 8501-1 addresses visual assessment of rust and preparation grades; ISO 8503-1 covers surface-profile comparators. An AMPP near-white metal blast-cleaning standard defines another specific route. Select the one called up by the project and primer; this article does not prescribe one grade for every job.

Visible cleanliness does not establish that water-soluble salts are acceptable. In salt-bearing environments, specify a sampling method and acceptance limit rather than assuming blasting has removed them. ISO 8502-6 describes extraction of water-soluble contaminants using the Bresle method, with ISO 8502-9 covering conductometric determination. Inspect and remove dust and spent abrasive before coating. Recheck steel if rain, condensation or a long delay occurs after preparation.

Give details their own preparation step

Weld spatter, sharp cut edges, laminations, crevices, bolt assemblies and drainage traps demand attention before the full coat. ISO 8501-3:2025 addresses preparation grades for welds, edges and other imperfections. Confirm the specified grade and repair of fabrication defects with the project team. A stripe coat on edges, welds and difficult geometry can help achieve continuous coverage, but it does not replace the specified full coat or correct an inaccessible design. Record what was prepared and inspected before subsequent layers hide it.

Select a complete ALKA system

Each layer has a separate job: a primer protects the steel interface, an epoxy intermediate builds the barrier and an exterior polyurethane finish maintains the specified appearance. ALKA’s published system pages provide these starting points:

“Surface tolerant” still requires contaminant removal and a defined preparation standard. For simple enamel work, ALKA-401 is described as a short-oil alkyd zinc-phosphate primer for compatible alkyd or synthetic enamel systems; it is not interchangeable with a zinc-rich epoxy specification. Another published system, ALKA-9931, calls ALKA-416 a zinc-phosphate epoxy primer, whereas the ALKA-416 product information identifies a one-pack zinc-rich cold-galvanising coating. Resolve that product-code and chemistry discrepancy with ALKA before incorporating ALKA-416 into an approved build.

Turn the concept into an inspectable specification

For each coat, identify the actual product, component set, colour, nominal and permissible dry-film thickness, method of application, maximum and minimum overcoating intervals, and required surface condition before the next coat. Agree any seal or mist-coat step over zinc-rich primer, stripe-coating sequence and procedures for handling damage during transport and erection. Set the environmental limits, cleaning and repair method from technically approved product data; a generic system diagram is not a mixing or application instruction.

Hold points should cover prepared-steel acceptance, contamination tests where specified, surface profile, primer continuity, edge coverage, coat thickness and finished appearance. ISO 19840 gives a procedure for checking dry-film thickness on rough surfaces; use the measurement and acceptance method named in the contract. ISO 12944-7 addresses execution and supervision in shop and field work. Retain the records of batches, conditions, readings, deviations and repairs for later maintenance.

Send ALKA the asset drawings, environment, substrate history, access, preparation constraints and performance requirements. Obtain a coherent, current, technically approved coating schedule and SDS set before work starts. Where severe chemical, immersion, splash or tidal conditions apply, ask for a separately specified system.

Frequently asked questions

Can a new coating go over old steel paint?

Possibly, if the existing paint is sound, adherent and compatible after the specified cleaning and preparation. Trial the proposed complete repair build and inspect the interface. An unknown or delaminating coating should not become the foundation of a new protective system.

Is visual blast cleanliness enough to accept the steel?

No. Profile, dust, soluble salts where relevant, welds, edges and current weather conditions also matter. The agreed inspection plan determines which tests and acceptance limits are required.

Does a zinc-rich primer make an external steel system suitable for immersion?

No. Atmospheric, splash, tidal and immersed duties require separate assessment and specifications. The approved complete system, substrate preparation and documented exposure determine suitability.

Technical references

• ISO 12944-2, environment classification; ISO 12944-5, protective paint-system selection; ISO 12944-7, execution and supervision.
• ISO 8501-1, visual cleanliness; ISO 8501-3:2025, welds and edges; ISO 8502-6, water-soluble contaminant extraction; ISO 8503-1, surface profile.
• AMPP guidance on structural-steel coating systems; ISO 19840, dry-film thickness verification on rough surfaces.