Why Aromatic Polyurea Changes Color in UV, and When to Go Aliphatic

Every applicator has seen it. A bright white liner goes out the door, and a season later it has turned creamy tan. A red deck slowly drifts toward pink. The customer calls, and you have to explain that the coating is still doing its job. The reason is chemistry, and once you understand it you can pick the right system before the first drum is opened.

Why aromatic polyurea changes color

Most spray polyureas, including many of ArmorThane's workhorse products, are aromatic. The isocyanate side (typically MDI based) contains benzene rings. Those rings are a big part of why aromatic polyurea is tough, fast and affordable.

The catch is sunlight. UV energy and oxygen attack the aromatic groups and convert them into quinone-type structures. Quinones are colored compounds, and because they form inside the polymer backbone, the yellowing cannot be washed off or reversed. The HighLine 510H TDS says it plainly: because of its aromatic composition, it will tend to yellow or darken after UV exposure.

What about chalking?

Over long exposure, the very top of an aromatic surface also oxidizes into a dull, powdery film. That is what applicators call chalking. You see it as faded gloss and a residue that wipes off on your hand.

Aromatic vs aliphatic at a glance

Aliphatic isocyanates have no aromatic rings, so they cannot form those quinone structures. That is the whole trick, and it is why aliphatic materials cost more and are used where color counts.

HighLine 410: ArmorThane's aliphatic polyurea

ArmorThane sums up HighLine 410 in one line: your whites stay white, and your reds don't turn pink. It is a fast setting, rapid curing, 100% solids, aliphatic spray polyurea for interior and exterior concrete and metal, and ArmorThane describes it as intrinsically UV resistant. It also meets USDA criteria and can coat carbon or mild steel without a primer.

The other route: aromatic base plus aliphatic topcoat

ArmorThane's guide describes a common hybrid approach: an aromatic base coat for performance and an aliphatic topcoat for looks. ArmorThane offers two options:

• UV ColorCoat: a UV resistant, 1:3 plural-component, solvent-based aliphatic polyurethane topcoat. Coverage is 1 gallon per 300 square feet, applied by brush, resin-core roller or HVLP at 35 to 45 psi. Two coats are normal, three for maximum protection, and it allows custom color matching.
• UV Topcoat: a two-component acrylic polyurethane with a semi-gloss finish, sold in 1 and 5 gallon kits in white, Battleship Grey, Gunsmoke Grey, Stone Grey, Sandstone and Tan.

When to choose which

Go full aliphatic with HighLine 410 when:

• Color is the product, such as branded colors, safety colors or decorative work.
• You want a single system with no second trade or second cure window.
• The surface is exposed concrete or steel like parking decks, walkways or refinery structures.

Use an aromatic base plus an aliphatic topcoat when:

• You need a thick, heavy-duty build and only the surface needs to hold color.
• Budget is tight, and the extra labor of a topcoat costs less than an aliphatic build.
• The customer wants a custom color match, which UV ColorCoat is designed for.

Skip the UV plan entirely when the coating lives in the dark, like tank interiors, buried structures and under-slab containment, and you can use the aromatic material best suited to the job.

Spraying HighLine 410 right

• Precondition material to 70 to 90°F and spray above 150°F through a high-pressure plural-component proportioner.
• Keep the surface at least 5°F above the dew point.
• Agitate Side B one minute per gallon, never dilute, and keep desiccant dryers on both drums.
• Spray multidirectional passes, and remember it is for trained, commercial applicators only.

HighLine 410, UV ColorCoat, UV Topcoat and our aromatic polyureas are all in the coatings and chemicals collection. Not sure which way to go on a bid? Call the tech line at (417) 831-5090.