What causes bubbles in paver sealer?

Concrete is porous, and ChemMasters notes that exterior concrete usually contains a meaningful amount of air. Euclid Chemical, writing about concrete sealers, describes the ordinary case: "Outgassing from the concrete surface during sealer application should be free to quickly move through a thin, wet sealer film." Its example of that film's thickness: "one coat of an acrylic concrete sealer should be about 5 mils thick when wet. When dry, the sealer is only about 2 mils thick," against a sheet of copy paper at about 10 mils.

A film that thin lets escaping air pass through it while it is still wet. The trouble starts when the film is thicker than that, or hardens before the gas underneath can get out.

Euclid names the direct mechanism: "When the sealer is applied too heavily, the air displaced through the surface can't escape, and it forms a bubble in the sealer surface." ChemMasters, writing about acrylic sealers on concrete, calls over-application "the third, and most common cause of bubbling," and separately names an overly vigorous roller as its own cause: "When applying the sealer with a roller, it is possible for an overly vigorous application to entrap air in the sealer; a common occurrence when using a long nap roller." Roller technique in general is covered on sealer roller marks and back-rolling.

The second path runs through temperature rather than thickness. Euclid explains that bubbling can also occur when application happens in hot weather or direct sun: the sealer skins over and dries on the surface before all of the solvent underneath has evaporated, and the pressure of that trapped solvent trying to escape forms the bubble.

ChemMasters names a related, porosity-driven version of the same problem: rising surface temperatures can expand the air already inside porous concrete enough to blow bubbles in a sealer applied on top of it. Named temperature limits for sealing, and the makers' own numbers for them, are covered on what temperature is too hot to seal pavers and sealing pavers in Naples summer heat.

ASCC's glossary defines bubbling by timing: gas trapped in the film "while it's soft, but after it has hardened sufficiently to prevent the gas from escaping." Its troubleshooting table adds that sealer placed on a hot surface will bubble or crack shortly after installation.

Bubbling of the hot-weather kind, in ASCC's words, leads to peeling or flaking; how a sealer peels is covered on why paver sealer peels. ChemMasters' name for the milky look the same over-application can leave is defined on the blushing glossary entry, and too much sealer shows in other ways too, set out under other signs of an over-applied sealer.

Correcting a bubbled film, whether by a solvent re-form or removal, is the sealer maker's procedure to publish, not a general instruction. Once a sound film has cured, the everyday questions take over: whether it still collects grime, covered on whether sealed pavers still get dirty, and whether it can take a pressure washer, answered on pressure washing sealed pavers.