Industrial Coatings & Surface Treatment

Powder wins where its conditions are met: a conductive part that can take the bake, a desire for thick, durable, uniform film in one coat, and volumes that fit a coating line, with essentially no solvent emissions to permit. Liquid systems win where parts cannot be baked, where films must be very thin or exactly color-matched across materials, where field application and repair are required, and for the engineered multi-coat protective systems that structures and immersion service demand. Recesses challenge electrostatic application either way, and finish quality is better in both runs on pretreatment than on the topcoat. Many parts could go either way, in which case the deciding factors are the bake tolerance, the required film build, and which local shops run which process well.

They are different products sharing a chemistry. Zinc electroplating deposits a thin, smooth, paintable layer suited to indoor and mild service, specified by class and usually paired with a supplementary conversion treatment. Hot-dip galvanizing immerses the fabricated part in molten zinc, forming a much thicker, sacrificial coating that protects it for decades outdoors, at the cost of a rougher finish, dimensional growth on threads, and design rules for venting and draining that the galvanizer should review before fabrication is finished. Between them sit zinc-rich paints and mechanical zinc. The words are not interchangeable on a drawing: cite the governing specification with its class or grade, and choose by the environment and life required, not by which word the last drawing used.

Anodizing converts the aluminum surface itself into oxide, in types the governing specification defines: the common decorative and corrosion-protective anodize, thin, dyeable, and the default for housings and machined parts, and hardcoat, many times thicker, built for wear surfaces, slides, and abrasion, at the cost of dimensional growth that the drawing must allow for and a limited color range. Choose hardcoat when parts wear against something, and the standard type otherwise. Two properties surprise buyers: anodize insulates, so grounding points must be masked and called out, and color consistency across lots has limits the finisher should discuss honestly. Specify the type, class, thickness where it matters, sealing, and masked areas; the callout is complete.

It tells you how a coating performed in a standardized fog cabinet for that many hours, which is a legitimate comparison between coatings tested the same way and a good check that a finisher's process has not drifted. It does not reflect years of service because the cabinet's continuous salt fog resembles almost no real environment, and rankings can even reverse between the cabinet and the real world, which is why cyclic tests that alternate salt, humidity, and drying exist. Use salt spray in specifications as a benchmark, with a stated duration and evaluation criteria; use cyclic testing when you need greater realism; and use the corrosivity category framework to specify what the coating must actually survive. Distrust any translation of cabinet hours into a warranty.

The part: drawings or models with material and its exact alloy or grade, dimensions, weight, and quantity, because mass drives bake and racking drives price. The finish: the specification with type and class, thickness, color and gloss with the standard they are judged against, and every masked area defined unambiguously. The duty: the environment or corrosivity category, any adhesion, corrosion, or thickness acceptance tests with their methods, and certifications required with shipment. The constraints: temperature limits, sealing surfaces, threads, and where rack marks may fall. And the logistics: packaging, protection, and turnaround. The items most often missing are the masked areas and the acceptance methods, both of which are cheap on the RFQ but expensive in a dispute.

The surface, not the coating. Failures overwhelmingly trace to preparation and pretreatment: contamination left under the film, a cleanliness grade or profile the system never got, blast-cleaned steel that waited too long before priming, a skipped conversion coating, or a cure the part's mass never actually reached. The coating that peels was usually never attached. This is why specifications lead with preparation grades, profile, and pretreatment, why inspection during application, of preparation, thickness per coat, and cure, outperforms inspection of the finished job, and why a finisher's pretreatment line and process controls deserve more of your qualification attention than their color booth. When a failure occurs, the failure mode and location usually indicate the missing step.

That several traditional finishes, chromate conversion coatings, some passivates, and decorative chromium historically used hexavalent chemistry that is restricted or burdened in major markets by European product rules and controlled as a workplace exposure in the United States. That leaves trivalent and alternative chemistries to serve most uses. The buyer's problem is that the same callout can often be satisfied either way and the part looks identical. So: know which markets and customer requirements your product faces, specify the chemistry family explicitly rather than only the finish name, obtain compliance declarations for the exact process used; and requalify anything sensitive when a finisher converts chemistries, because performance is close but not always identical. Silence in the specification means the shop decides.

It is the environment classification in the international protective coatings standard, running from heated interiors through industrial and coastal atmospheres to the severest exposures, with separate categories for immersion, each mapped to proven coating system types at defined durability levels. It exists so an owner can state the problem instead of guessing at solutions: classify the environment, state the required durability, and let systems be proposed against that requirement. Use it in RFQs for structures, equipment, and assets exposed to weather or chemicals, and use it to test bidders, because a coating proposal that cannot situate itself within the framework is marketing. For factory-finished products, the framework still helps you say how hard the service is in words the industry shares.

When the coating is protecting an asset whose failure is expensive: structural steel, tanks and linings, bridges, marine and immersion service, and any field-applied protective system with a meaningful warranty. The industry association operates contractor qualification programs and training. It certifies coating inspectors and owners in the protective world, routinely requiring both, because application quality, preparation, ambient conditions, coat thickness, and cure are where systems succeed or fail. Independent inspection during the work is far cheaper than litigation after it. For shop finishing of manufactured parts, the equivalent is qualifying the finisher: their pretreatment, process controls, and acceptance testing. Scale the formality to the consequence of failure, and put inspection hold points in the contract, not in hindsight.