Does paver sealer turn yellow?

ICPI sorts the question by chemistry and by purpose. Acrylics developed specifically for concrete pavers, in its words, “do not yellow over time.”

Aromatic urethanes are the family ICPI singles out for the opposite reason: “Aromatic urethanes should contain an ultra-violet (UV) inhibitor to reduce yellowing over time. The product label should state that the sealer is UV stable.” The same document credits water based epoxy sealers with resisting “most chemicals and degradation from UV radiation,” a line about the film holding up, with no yellowing claim attached.

ICPI's inhibitor line is written for aromatic urethanes, one kind of urethane sealer, and its check sits on the container: the label, ICPI says, should state that the sealer is UV stable. When a surface is resealed, ASCC notes, the original sealer is typically unknown, not only the manufacturer but the type.

ASCC, writing about sealers on poured and decorative concrete, defines the problem in one line, “Sealer turns yellow in areas exposed to UV rays,” and gives it three probable causes: a non-yellowing sealer that was not used in the first place, layers of sealer that have separated, and UV inhibitors that lose strength as the sealer ages.

The second cause reads as an adhesion problem as much as a color one. Separation between the layers of sealer, in ASCC's words, “will act and appear almost identically to some of the adhesion issues,” the separation of coating layers that the term delamination names. Its prevention is a thoroughly clean, dry surface before resealing, so moisture is not trapped between the layers.

None of this says whether a sealer keeps the paver's own color from fading in the sun; that is a separate question, taken up under whether sealer protects against sun fading.

ASCC's troubleshooting for its own material ends in one place: “Once a sealer has yellowed the only proper fix is to strip and reseal, otherwise the yellow coating will be trapped under the new sealer.”

That instruction is ASCC's, written for sealers on poured and decorative concrete. Its whitening entry turns to stripping only after other remedies fail; its yellowing entry names strip and reseal as the only proper fix, because a new coat would trap the yellow film under it.

What stripping a sealer means is defined on its own page, and whether it suits a given film is the sealer maker's call. Whether a worn film can take a fresh coat at all also depends on its chemistry, set out under what a sealer is carried in and what happens when it wears.