Salt Attack

a Report by David Young

Read Page 45 or Paragraph 14.3

"Captive-Head Washing

These systems use a water jet spray within a hood or jacket which also contains a powerful vacuum to capture the dirty water and prevent it being spread over the masonry. They are used principally for cleaning dirt and grime from walls, and have some potential to remove surface and near surface salts, although there is limited experience with their use for this purpose. They will only ever be partially effective, as they must compete against the initial high capillary suction of the masonry, which will draw some of the water inwards, taking some salt with it.
Captive-head washing may be a useful way of reducing surface salts in bricks and stones prior to sacrificial repointing of the joints. That way the new mortar will have less salt to contend with and should last longer. An alternative would be to use a poultice, which would remove more salt, but which may not be warranted in many cases, particularly given the relative ease and speed of the captive-head washing. The choice will be a compromise between the need to remove salt and the complexity and cost of the treatment.
Other washing treatments have been tried without much success. They have generally been based on a period of spraying the walls with a fine mist, followed by a drying phase to bring the salts to the surface, and then either flushing the salts off with more water, or sponging them off by hand with damp sponges."

Salt Attack by David Young

Link to the report can be found here at the NSW Goverment website

To download click here