This white stuff is known as efflorescence. All concrete products contain cement which produces lime or water soluble calcium oxide. Lime can also be in the bedding sand, aggregate base materials, or soil. Moisture from rain, sprinkler systems, underground sources, poor site drainage or dew enters the microscopic capillaries that run from the interior to the surface of the paver. Calcium oxide inside the paver reacts with the water in the capillaries and forms calcium hydroxide. This rises to the surface and reacts with carbon dioxide in the air, and forms a white haze of calcium carbonate. When moisture on the surface evaporates, the white haze of efflorescence becomes visible. This is not a permanent condition nor is it a defect. It is a natural byproduct of hardened concrete and will stop when all of the calcium hydroxide is released from the pavers. Cleaners are available to speed up the process.