Efflorescence is one type of white deposit found on masonry. It is formed by water, within the construction material, reacting with the natural salts contained within them and the mortar. These salts dissolve in the water and are carried to, and deposited on the surface, by the natural evaporation that occurs by air coming into contact with the surface of the wall or floor.

External White Marks - Efflorescence or Free Lime?

Under normal circumstances, white, fluffy efflorescent salt occurs in relatively new buildings because the brickwork was not protected during construction and has become wet. This water will find its way out, through evaporation, and the salts can be brushed off and should not re-occur. However, if a lead flashing is damaged, or joints are missing and water is allowed to continuously enter the construction material, efflorescence will continue to form. In this situation the cause must be found and eradicated. There is a treatment for efflorescence, Salt Neutraliser, which can be used after the cause has been eliminated, but this will only be successful if; * No more water is passing through the wall * It can be applied to bare plaster, render, stone or brick – it will not pass through paint * Other causes of white patches have been investigated and ruled out The other causes of white patches worth checking are; * A water leak – gutter or downpipe leaks, cistern overflow running, mains pipe weeping * Penetrating damp – e.g. via a blocked cavity or poor pointing * Free Lime – the result of mortar or concrete curing, or from some clays used in brick making The most effective treatment for efflorescence and free lime staining on external surfaces is time. The natural weathering of the surface, if maintained, will remove it. For a build up of deposits on a wall, a good scrub with a dry, stiff brush will remove the worst, but make sure you follow it with a soft brush to move the salts away from the wall entirely. They will stay in the pores of the brickwork and dissolve again when it is wet. Treatments, such as acid etc, generally involve getting the surface, and the salts, wet again. This dissolves them and carries them into, not out of, porous surfaces. Mortar Stains – Residual Sand and Cement Left During Construction Mortar stains are best dealt with by using a brick cleaning acid. These are available from most DIY stores and all Builders’ Merchants. Follow the instructions on the tub and either apply the acid in diluted or undiluted form, and then wash off. Take precautions by wearing gloves and masks; acid is dangerous. For large lumps of mortar, gentle persuasion with a chisel will take them back to the surface of the wall, where a quick rub with a wire brush will take you down to the stain which the acid should remove. Do not "attack" large lumps with acid. Internal White Marks – Efflorescence on Plaster or Behind Paint and Wallpaper The white, fluffy salts that sound ‘cruchy’ to the touch can occur beneath wallpaper or paint and the crystals are strong enough to push the coatings off the plaster. This kind of sulphate crystal build up can occur in any building, new or old, where water is passing into the structure. This water will find its way out through evaporation and the salts can be brushed off, but they frequently re-occur. In this situation the cause must be found and eradicated. The treatment for efflorescence, Salt Neutraliser, can be used after the cause has been eliminated, but this will only be successful if no more water is passing through the wall. It must be applied to bare plaster, render, stone or brick – it will not pass through paint. Damaged Interior Wall Check for; * An external water leak – gutter or downpipe leaks, cistern overflow running, mains pipe weeping, and window frame mastic missing. * An internal water leak – radiator pipes, sewerage pipes, mains water pipes * Penetrating damp – via a blocked cavity or poor external pointing, high abutting garden wall Damaged Wall Plaster – How to Rectify If the damage is localised than patching is possible, but generally affected areas need to be hacked back to the bare wall. It is then essential to either replaster to the correct Specification for a damp wall (do NOT use modern, lightweight Gypsum-based plasters) or to use a Membrane Lining System. Property Repair Systems will provide free of charge calculations and costings for all types of repairs using waterproof render/plaster and Membrane Systems. Consult their experts for damp proofing, replastering and lining systems.