It is chemistry, not product quality
Ambering is not a defect and it is not a sign of a cheap product. It is what aromatic epoxy resins do under UV, and it happens to expensive epoxy exactly as it happens to inexpensive epoxy. The molecular rings that give the resin its hardness are also what absorb ultraviolet energy and rearrange, and the resulting compounds are yellow. No epoxy clear coat is exempt from this, whatever the marketing says.
Where it shows up first
Follow the light. In a garage it is the strip inside the door where afternoon sun reaches, in a sunroom it is the area under the glazing, and in a commercial space it is under a skylight. The contrast is what makes it obvious: the yellowed area sits next to an unexposed area that has not changed, so the eye reads it as a stain rather than as gradual change. Under a couch it is invisible until the couch moves.
What actually prevents it
An aliphatic topcoat, which in floor systems means polyaspartic or an aliphatic urethane. These are formulated without the aromatic rings that absorb UV, so they hold their colour indefinitely in sunlight. This is the single reason every decorative floor we build finishes in polyaspartic rather than in an epoxy clear, and it is why we can put a white or pale floor into a glazed room without it being a two year mistake.
Can a yellowed floor be fixed
Yes, and it is a manageable job rather than a rebuild, provided the coating is otherwise sound. The ambered topcoat is abraded back mechanically and a fresh UV-stable topcoat goes over it, which restores the colour and prevents recurrence. What cannot be done is bleaching or cleaning it out. The colour change is in the cured resin itself, not on it.
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