Follow treatment recommended for 'Mortar and mortar smear'.
In older brickwork lime staining originating from the reinforced concrete structure can be particularly difficult to remove. It is important to stop the flow of moisture through the structure to overcome the problem.
Wash down with a 20% solution of Potassium Hydroxide. Do not wash the wall with clean water afterwards. (Hydrochloric acid should never be used on vanadium stains since it 'fixes' them and turns them brown.)
6. EFFLORESCENCE (WHITE CRYSTALS OR WHITE FURRY DEPOSIT)
This usually disappears rapidly from new brickwork by the action of wind and rain. Brushing sponging down the wall at times of maximum efflorescence will also help. The salts brushed off should not be allowed to accumulate at the base of the wall, otherwise they may be carried back into the brickwork by subsequent rain.
7. LICHENS AND MOSSES
These can be killed with a solution of Copper Sulphate (1 kg to 10 litres of water) or a proprietary weed killer. Vegetable growth is generally indicative of damp brickwork and will usually reappear if this basic cause is not cured. (Green staining which does not respond to this treatment is probably due to Vanadium salts from within the bricks.)
8. RUNNING WATER
Water running regularly down the surface of brickwork produces pattern staining and this can usually be removed by scrubbing after wetting with a high pressure mist spray of cold water. If this is not effective, the treatment recommended for mortar should be followed.
Moisture movement concentrates salts and is the main cause of all staining.
9. VARIOUS OILS
Sponge with white spirit, carbon tetrachloride or trichloroethylene. Good ventilation is essential if volatile solvents are used indoors.
Apply commercial paint remover or a solution of trisodium phosphate (1 part to 5 parts of water by mass), allow the paint to soften, and remove with a scraper. Wash the wall with soapy water and finally rinse with clean water.
11. RUST OR IRON
Wash down with a solution of oxalic acid (1 Part to 10 parts of water by mass). (Brown staining which does not respond to this treatment, particularly at the junction of the brick and mortar, is probably due to manganese).
12. MANGANESE (DARK BROWN)
Brush the stain with a solution of 1 part acetic acid and 1 part hydrogen peroxide in 6 parts of water.
13. TIMBER (BROWN OR GREY)
These stains are due to water spreading tannin or resin from the timber across the bricks and mortar.
Normally they can be removed by scrubbing with a 1:40 solution of oxalic acid in hot water.
14. SMOKE AND SOOT
Scrub with a household detergent. The more stubborn patches can be removed from the brick pores using trichloroethylene, although good ventilation is needed if this is used indoors.
Except where bricks are liable to surface damage, remove excess tar with a scraper, then scrub with water and an emulsifying detergent. If necessary, finally sponge with paraffin. Do not wet brickwork with water first.
16. LARGE PROJECTS - MULTI STOREYED BUILDINGS
Sandblasting is not recommended as a solution although it has been used special instances overseas.
High pressure cleaning is suitable if well managed by experienced contractors and with agreement and pre planning between the architect, contractor, sub-contractor and brick manufacturer.
- Hand labour should be used to remove large mortar particles.
- Cleaning should only start about seven days after the building is complete, when the mortar is set.
- metal, glass, wood surfaces, etc: should be appropriately masked.
- Cleaning should commence at the top of the building, working downwards.
- The walls should be saturated with clean water before chemicals are applied.
- Choice of application pressures and chemicals are critical to the operation.