The white ‘bloom’ you have noticed is efflorescence and can happen if incomplete brickwork is allowed to get very wet during construction. The water carries soluble salts to the surface of the brickwork and when it evaporates, leaves behind a white, powdery coating. A brick’s salt content is classified as L for low and N for normal, so it stands to reason that low salt content bricks are less likely to suffer from efflorescence. However, salts in the mortar and groundwater can cause efflorescence too. It can be prevented by making sure that large amounts of water don’t enter unfinished brickwork. Efflorescence will in any case weather away naturally. However, it is possible to remove it by brushing with a soft bristle brush and sponging down any remaining deposit with clean cold water.