Efflorescence on walkway

I have an increte walkway and a white chalky substance is appearing. The walkway is sealed and it appears that it might be under the seal coating. someone told me that it could be moisture coming to the surface and being trapped under the sealer and that when things heat up and dry out it should disappear. what do you think? new york city

That explanation is not very clear. IF it was sealed to the point that moisture cannot pass through, then the white substance (efflorescence) would not appear. If it can move through, then the powder would appear on the surface. Besides, when moisture gets trapped under a sealant it will cause it to fail by de-bonding. That is why these sealants are designed to "breath" and let vapors pass through. Efflorescence is the result of moisture moving through the concrete and evaporating from the surface. Salts that are drawn from inside the concrete crystallize on the surface. Under a magnifying glass you may see the crystals. Drying does not make it go away. You can brush it or wash it away, but it will return as long as there is moisture in or under the concrete, and the top surface is exposed to dry air. Efflorescence is not considered a problem beyond appearances unless there are Sulfates in the soil in very high concentration. I really doubt that it would be a problem in your case. I am not familiar with the Increte brand name.