Most purchase orders for painted aluminum sheet name a color and a gauge and stop there. That is not a coating specification, and the difference shows up four or five years later on a south elevation.
Two coils can carry the same RAL number, the same substrate, and the same thickness, and still be different products. One holds its color for a decade. The other chalks and fades inside five years. Nothing on the order distinguished them.
Here is what actually goes on a coating spec, and how to read the one a supplier sends back.
What prepainted actually means
Prepainted coil, also sold as color coated aluminum coil, is produced on a continuous coil coating line. The strip unwinds and runs in sequence through cleaning, a chemical conversion pretreatment, primer, then topcoat, each cured in an oven before the coil is rewound. Line speed, oven temperature, and film thickness are controlled and logged across the whole coil.
Three consequences follow from that, and they are the reason coil coating exists as a separate process rather than a cheaper version of spray finishing.
- Film build and color are measured continuously rather than sampled after the fact, so variation across a coil and between coils of the same order is small.
- Coil coatings are formulated to be applied flat and bent afterward. The T-bend test exists specifically to qualify that.
- Both sides in one pass. Backcoat goes on in the same run, which matters for anything that will be laminated, foamed, or exposed on the reverse.
The tradeoff is that the coating is chosen before the part exists. You cannot decide the color after forming, and the coating has to survive whatever forming comes next.
The specification framework that matters in North America
North American architectural work is written against three voluntary specifications published by AAMA, now part of the Fenestration and Glazing Industry Alliance. They cover organic coatings on aluminum extrusions and panels, and all three carry a coil coating appendix, so they apply directly to coil coated product and not only to spray applied finishes. The current revisions are the 2026 editions: AAMA 2603-26, 2604-26, and 2605-26.
The tiers are usually described as good, better, and best, but the real difference is how long the coating sat outdoors in South Florida before it could carry the designation.
| Specification | Florida exposure | Salt spray | Common coating chemistry | Where it fits |
| AAMA 2603 | 1 year | 1,500 hours | Standard polyester | Interior, residential, mild exposure |
| AAMA 2604 | 5 years | 3,000 hours | Super durable polyester | Most commercial and institutional work |
| AAMA 2605 | 10 years | 4,000 hours | Fluoropolymer, commonly 70% PVDF by weight of resin solids, though FEVE systems also qualify | Facades, monumental work, coastal and high UV |
The gap between the tiers is not incremental. AAMA 2603 sets no gloss retention requirement at all, while AAMA 2605 requires at least 50 percent gloss retention after ten years of south facing Florida exposure, a color change of no more than 5 delta E, and a chalk rating of 8 or better. A product can fully comply with AAMA 2603 and still visibly chalk and fade on a building within a few years.
That is worth knowing on both sides of the order. If you are buying, an unqualified reference to AAMA 2603 in a spec gives a fabricator a defensible route to submit something far below what the architect intended. If you are selling, quoting against the wrong tier is how a job turns into a warranty claim.
Resin families and where they land
Coating systems are usually named by resin family. The names describe chemistry, not a guaranteed performance level, and actual durability depends on formulation, film build, pretreatment, and the service environment.
- Polyester (PE). The volume system. Interior work, ceilings, light commercial, and applications where the finish will be replaced or repainted on a shorter cycle.
- High durable polyester (HDPE). Reformulated for longer exterior service. This is the family that super durable polyesters qualifying to the five year tier come from.
- Polyurethane and polyurethane polyamide (PU, PUPA). Chosen where the coating has to take abrasion and handling, including roller shutter slats and products that get worked hard after forming.
- Fluoropolymer chemistry, and the usual route to the ten year tier. Architectural specs frequently call for 70 percent PVDF by weight of resin solids, though the standard itself is written around performance rather than resin content, and other qualifying fluoropolymer systems such as FEVE can meet it.
- Epoxy and epoxy polyester. Primarily backcoats and applications where adhesion under lamination matters more than weathering.
Cost generally rises with coating system performance and complexity, though metallic pigments, layer count, film build, and small color runs can upset the order. The practical question is not which resin is best, it is which tier the application actually needs, because specifying a fluoropolymer for an interior ceiling panel is as much of an error as specifying standard polyester for a coastal facade.
What the tests actually measure
A coating datasheet is a list of test results. These are the ones worth reading.
| Test | What it tells you |
| T-bend | Whether the coating survives forming. The number is how many thicknesses of the substrate the bend radius equals. Lower is more demanding. |
| Cross-hatch adhesion | Whether the coating system is bonded to the substrate. Failures can point to cleaning, pretreatment chemistry, cure, or primer and topcoat compatibility. |
| Salt spray | Corrosion resistance at cut edges and scribes. The requirement climbs across the tiers: 1,500 hours for 2603, 3,000 for 2604, 4,000 for 2605. |
| Accelerated UV | Early indication of fade and gloss loss, run per ASTM G154 or G155. It supports the Florida data, it does not replace it. |
| Gloss retention | Percentage of original gloss remaining after exposure. AAMA 2605 requires at least 50 percent after ten years. |
| Color change (delta E) | How far the color has moved. AAMA 2605 caps it at 5 units. |
| Chalk resistance | Surface powdering as the resin erodes, rated per ASTM D4214. AAMA 2605 requires a rating of 8 or better. |
Ask which standard each result was run under. Outside North America, the same properties are commonly reported against EN references rather than AAMA and ASTM, and the numbers are not always directly comparable. A supplier shipping into multiple markets should be able to tell you which reference set a given result belongs to.
Film build, sides, and the backcoat nobody asks about
Two specification details get left off orders routinely and cause problems later.
The first is film thickness. Minimum dry film build increases across the three tiers, and the extra build is part of how the higher tiers reach their performance. Do not carry a number across from a spray applied spec, though: the coil coating appendices set their own film thickness provisions, and they are not the same as the main body requirements. Check the appendix for the tier you are specifying. If a quote comes back cheaper than expected, film build is the first place to look.
The second is what happens on the reverse. Coil can be coated on one side, or on both sides with primer on the back. Which one you need depends on whether the reverse face is exposed, bonded, or in contact with insulation or another metal. It is a cheap decision to make at order time and an expensive one to discover after forming.
Protective film is a third item worth naming explicitly. On dark colors and on anything handled repeatedly before install, it is the difference between a clean job and a punch list.
The mill behind the coil
Coating capability varies more between producers than substrate capability does, so it is worth checking against the spec rather than assuming.
Primealux Alloys supplies coil produced by Orbit Aluminum Industries, which runs casting, rolling, and coil coating on one site in Aqaba, Jordan. Prepainted coil is available up to 1350 mm wide and 1.60 mm thick, coated one side or two side with primer, on aluminum or steel substrate. Coating systems include PE, HDPE, PVDF, PU, PUPA, epoxy, acrylic, and epoxy polyester, in any RAL reference or custom match, with solid, metallic, woodgrain, brushed, and textured finishes available.
Coated product is tested against ASTM or EN references depending on the destination market, covering salt spray, UV, T-bend, adhesion, gloss retention, and color difference, with material certificates issued per batch. Where a project calls for a specific AAMA tier, ask for the qualification on that system rather than inferring it from the resin name. Recycled content coil is available on select alloys and traceable to the cast batch.
What to put on the order
A coating specification a supplier can quote against answers all of these:
- Alloy, temper, thickness, width.
- Coating system. Resin family, and the performance tier if the project names one.
- Film build. Total dry film thickness, and the layer structure.
- One side, or two side with primer, and what the reverse face has to do.
- RAL or a submitted sample, gloss level, and whether a single production lot is required.
- Surface finish. Solid, metallic, woodgrain, embossed, brushed.
- The tightest bend the coating has to survive, stated as a T-bend requirement rather than described in words.
- Protective film. Yes or no, and peel timing if the product sits before install.
- Test reporting. Which standard set, and whether certificates ship with the material.
Quotes on coil to a submitted specification, including custom widths and custom colors, go through Primealux Alloys for North America. Material is produced to order by the mill against the spec rather than pulled from standing stock, so the answers above are what gets made rather than what happens to be on a rack.
One thing to check on every painted order
Ask which specification the coating system is qualified to, and ask for the document. A resin name on a quote is a description of chemistry. A qualification is evidence of exposure. On a facade that has to hold its color for the life of the building, only one of those is worth anything.
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