Yellowing, also called ambering, is the gradual amber or yellow tint some coatings develop over time when UV light breaks down the resin, most noticeable in clear epoxy topcoats exposed to sunlight.
Understanding Yellowing in Epoxy and Polyaspartic Systems
Standard epoxy resins are not UV stable. Sunlight breaks down the chemical structure of the cured film over months and years, producing a visible yellow or amber cast, especially in clear or light-colored coats. This is a cosmetic issue, not typically a structural one, but it’s one of the most common callback complaints on sunlit floors.
Why Epoxy Yellows and Polyaspartic/Polyurethane Doesn’t
Aliphatic polyurethane and polyaspartic topcoats are formulated to be UV stable and hold their color far longer under sunlight, which is exactly why they’re used as a clear topcoat over an epoxy base coat rather than leaving epoxy exposed as the final wear layer in sun-exposed areas.
Where Yellowing Shows Up Fastest
Garage floors near uncovered windows or open bay doors, patios, and any epoxy left as the final coat under direct or even indirect sunlight will show yellowing soonest. Areas that stay shaded or covered yellow far more slowly.
Preventing Yellowing With the Right Topcoat
The standard fix is system design, not a magic product: apply a UV-stable polyaspartic or aliphatic polyurethane topcoat over the epoxy base coat wherever a floor will see sun exposure, rather than leaving epoxy as the final layer.
Also Called
Ambering, UV Amber
