Soluble salts within the substrate are brought to the surface during the drying out of residual moisture. Normally efflorescence has the appearance of white ‘fluffy’ crystals and once all excess moisture has dried from the substrate, these effects should cease. The presence of efflorescence in an existing building may indicate a structural problem, eg defective damp proof course or leaking pipe. All structural defects should be investigated and rectified prior to redecoration.