CategoryPowder Coating
Powder coating for steel: cure, film thickness, colour and what a quote needs
Powder coating is a dry, electrostatically applied finish that is baked onto the steel in an oven, giving a durable decorative and protective final coat. This page covers what actually decides the outcome: the cure window the part must survive, the film thickness it ends up with, how colour is specified, which features need masking, and what changes when the coating goes over hot-dip galvanized steel rather than bare metal.
What drives the price
- RAL colour or a custom match
- Film thickness requirement
- Part size and oven fit
- Surface prep and masking complexity
- Total volume
- Extra pretreatment if the part is already galvanized
What to send for a quote
- Grade or material number
- Form and dimensions
- RAL colour, or a sample to match
- Required film thickness, if specified
- Masking requirements — threads or machined faces
- Substrate — bare steel or already galvanized
- Whether you need an inspection certificate
- Delivery address and required date
Traceability and EN 10204 certificates
Standard for steel purchases: 3.1
The certificate belongs to the material, not to the coating. Powder coating does not create an EN 10204 certificate — the real question is whether traceability survives blasting, pretreatment and the bake, and how the coated piece is marked so that it does.
Standard-defined
Source: EN 10204 defines inspection-document types.
Cure temperature and time
Cure time is measured after the part itself reaches temperature, not from when it enters the oven.
Indicative figures. Confirm the exact cure schedule and film thickness with the powder manufacturer's data sheet for your product.
Indicative
Film thickness
Indicative figures. Confirm the exact cure schedule and film thickness with the powder manufacturer's data sheet for your product.
Indicative
Colour — the RAL system
Colour matching outside the standard RAL palette is possible; oven scheduling and any minimum quantity for a custom batch are provider-specific.
Standard-defined
Maximum part size
One supplier's published figure, not an industry norm. The maximum part any provider can coat is set by their own oven and pretreatment-bath size.
Supplier-published
Powder coating over hot-dip galvanized steel
Powder coating over hot-dip galvanized steel needs an extra step: thermal pretreatment before the powder is applied, to stop the zinc coating outgassing during the bake and blistering the finish.
Reported combined durability: roughly 1.5 to 2.3 times the lifetime of galvanizing or powder coating used alone.
Standard-defined
Masking
Threads and machined or mating faces are masked before coating and unmasked after cure — a coated thread risks cross-threading, and a coated mating face risks fouling a tolerance or a seal.
Indicative
Services
What cure temperature and time does powder coating need?
Standard epoxy and polyester powders on steel typically cure around 160 to 200°C, held for roughly 10 to 25 minutes once the part itself — not the oven — has reached that temperature. Those figures are trade consensus, not a spec: the actual cure schedule for a specific powder is set by that powder manufacturer's own technical data sheet, so confirm it with your provider for the product you're using.
How thick is a powder-coated finish?
General industrial powder coating typically builds a dry film of about 60 to 100 µm in a single coat, measured with an electronic gauge per ASTM D7091 or ASTM D1186. Heavier-duty and marine coatings are commonly reported thicker. Treat the range as indicative and confirm the specified thickness against the powder manufacturer's data sheet.
How is the colour specified — do I have to use RAL?
Colour is normally specified by its RAL Classic number — for example RAL 9005 for jet black or RAL 9010 for pure white — rather than by a verbal description, so the provider and the powder supplier agree on exactly the same shade. Matching outside the standard RAL palette is possible, but oven scheduling and any minimum quantity for a custom batch are provider-specific — ask before committing to a non-standard colour.
Can you powder coat over hot-dip galvanized steel?
Yes, powder coating is regularly applied over hot-dip galvanized steel as a decorative or extra-protective final layer, but it needs one step a bare-steel job doesn't: thermal pretreatment before the powder goes on, following the preparation practices in ASTM D7803, to stop the zinc coating outgassing during the bake and blistering the finish. Done correctly, per the American Galvanizers Association, the combined system reportedly lasts roughly 1.5 to 2.3 times the lifetime of either galvanizing or powder coating used alone. Tell your provider up front that the part is already galvanized.
Will threads and machined faces be masked?
Threads and machined or mating faces are masked before coating and unmasked after cure. A coated thread risks cross-threading against its mating part, and a coated mating face or bore risks fouling a tolerance or a seal — both are avoidable by masking rather than fixing afterwards. Tell your provider which features must stay bare.
Is there a maximum part size?
Maximum part size is set by the individual provider's oven and pretreatment-bath dimensions, so it varies. One supplier publishes a maximum of 10′ × 10′ × 28′ for their line as an example of the scale involved — check the actual oven size with your provider before you commit to a job.
Do I get an EN 10204 3.1 certificate?
This is the question worth asking carefully. EN 10204 defines inspection document types 2.1, 2.2, 3.1 and 3.2, and 3.1 is the usual buyer default in steel procurement. But powder coating does not create a certificate — the certificate belongs to the material. What matters is whether traceability survives blasting, pretreatment and the bake, and how each coated piece is marked so it stays linked to its heat. Ask the provider that directly.
What information do you need for a quote?
Send the grade or material number, the form and dimensions, the RAL colour or a sample to match, and the required film thickness if you have one. Say whether features like threads or machined faces need masking, whether the substrate is bare steel or already galvanized, whether you need an inspection certificate, and give the delivery address and the date you need it. That turns an enquiry into a firm price rather than a range.
Is there a minimum order quantity?
There is no industry-wide minimum order quantity for powder coating; it varies by provider, and some price small or single-piece jobs in a way that makes them impractical. Ask as part of your enquiry rather than assuming.
What is the lead time?
No general lead time can be stated honestly — it varies by provider, and with part size, colour availability and their current oven schedule. Ask for a committed date with your quote rather than planning around a general figure.
What is the difference between powder coating and priming?
Priming is a preparatory layer that protects the steel temporarily and gives a following coating something to bond to — it is not meant to be the finished surface. Powder coating is the finished, decorative and protective final layer, baked on and expected to stay on the part in service. A part can be primed and later powder coated; the two are different stages of the same protective build-up, not alternatives to each other.
What does powder coating cost?
Powder coating is not priced from a single rate, so any figure quoted here would mislead. What drives it is the colour or custom colour match, the required film thickness, part size relative to the provider's oven, surface prep and masking complexity, total volume, and whether the part is already galvanized and needs the extra pretreatment step. Send the items in the quote checklist and you will get a firm price instead of a range.
