Blushing

The ASCC Decorative Concrete Council's glossary defines blushing this way: "Commonly used to describe a sealer or cure & seal that has turned milky-white in appearance." The entry sits among coatings terms written for poured and decorative concrete, not for interlocking pavers.

The same guide treats sealer whitening under its own heading, in its troubleshooting pages rather than the glossary, and defines it by cause: "sealer whitening occurs when moisture (water vapor or solvent) is trapped in the layers of sealer. Can also be a result of sealer application taking place in cool or damp conditions resulting in poor film coalescence." The glossary entry for blushing names a look, and the guide keeps the two as separate entries.

The sealer makers use the word less strictly. Euclid Chemical, writing about solvent based concrete sealers, treats blushing and whitening as one condition, and ChemMasters, writing about acrylic sealers, calls a milky or whitened look under the film blushing.

Euclid Chemical, in a company article on concrete sealer problems, names two contributors to blushing in a solvent based concrete sealer. The first is application to a wet surface, where the sealer floats on trapped water instead of bonding. The second is "applying it too thick."

ChemMasters, writing about acrylic sealers on concrete, also ties the milky look to over-application: the same excess that traps solvent and raises bubbles in the film can leave a milky or whitened look underneath it, which it calls blushing. The bubbles themselves are covered at what causes bubbles in paver sealer.

Techniseal, a paver sealer maker, does not use the word, but its Product Guide gives the paver version of the wet-surface warning, a white film left where a Protector meets moisture. The wet-pavers question itself is answered at what happens when sealer goes on wet pavers.

ASCC's troubleshooting pages carry a warning worth reading before putting a name to any white surface: "Efflorescence and sealer whitening are commonly mistaken for each other." Efflorescence is a deposit that reaches the surface from the concrete or from what lies beneath it; a blushed or whitened sealer is a change in the film on top, from moisture or solvent caught in or under that film.

The deposit itself is defined at efflorescence.

ICPI, writing for interlocking concrete pavers, lists the conditions under which a sealer may whiten without using the word blushing. That list, in ICPI's own words, whiten and cloudy, is under why sealed pavers turn white or cloudy.