What causes fluffy crystal patches and hard, shiny film on walls?

Known as 'efflorescence', these effects appear as a result of salts crystallising in materials such as bricks and plaster or render. The fluffy deposits can be removed with coarse Hessian sacking or by dry brushing, repeated every few days until the deposits disappear. Hard, shiny efflorescence can be sanded to roughen the surface, then painted over. Conventional solvent-based paints should not be applied on new buildings where efflorescence occurs for at least 12 months, to allow the surface time to dry out thoroughly. Use Dulux Alkali Resisting Sealer prior to applying any water-based finishes. Alternatively, use Adhesion Promoting Primer for solvent-based paint.