Efflorescence is a deposit of white chalky crystals that can sometimes appear on the surface of concrete products and other porous building materials, which have soluble salts in them.
The primary cause is moisture; moisture must be present to pick up the soluble salts and transfer them to the surface of the concrete, the water evaporates, leaving behind an unsightly white chalky powder. Natural occurring salts are found in soil, water, gravel and cement are dissolved by rain and ground water.
To minimize the appearance of efflorescence, make sure the pavers are kept dry, so providing a properly draining base for the pavers to sit on is very important.
The efflorescence will wear off over time, but if you are in a hurry, using a stiff bristle broom and water may be a quick fix, however if the process has not stopped then the efflorescence will reappear and need to be cleaned again.
In stubborn cases of efflorescence, it can be removed using an efflorescence cleaner, make sure it has been specially formulated to be used on concrete or natural stone, making sure you follow the directions as listed on the container. Be sure to test in an inconspicuous area before cleaning the entire area.