Removing stains from brickwork
by Megan Macpherson
Mortar stains can be removed with hydrochloric acid, but what about other stains that can build up over a long period of time? The Clay Brick Association of NSW has some ideas for cleaning stains caused by timber, iron, grime, graffiti, smoke and oil from clay bricks. If you don’t know what the cause of the stain is, then test a cleaning method, and wait until it dries to see if it has worked or not. Any neutralisation of acid on a wall can be done with bicarbonate of soda solution.
Unsealed timber near brickwork will cause stains on bricks as water mixes with tannin and resins in the wood. Clean timber stains by scrubbing with a solution of 120 grams of oxalic acid per four litres of hot water, and then neutralising the wall. Another method is to use a bleaching solution containing sodium hypochlorite and allow it to dry on the wall.
Soil and dirt which has stained bricks can be cleaned by scrubbing with a bristled brush using detergent and hot water. Grime stains are prevalent in city areas, especially around industrial zones or train stations. To remove these stains scrub with a fibre brush and use liquid detergent.
Rust from steel, as well as welding stains on bricks can be removed by using a strong oxalic acid solution which should be a mixture of 500 grams of acid to four litres of hot water. Neutralise the wall afterwards.
Blue or green stains on bricks could be water running from something made from copper or bronze onto the brickwork. This can be removed by using either acetic or phosphoric acid. The ratio for the acetic acid mixture is one part acetic acid (80 percent or stronger), to one part hydrogen peroxide (30-35 per cent or stronger) and six parts water. The ratio for the phosphoric acid is one part phosphoric acid to three parts water.
If you have been doing renovations, there is a chance that there could be oil, bitumen or tar stains on your bricks. To remove these, you will need a commercial emulsifying agent, or degreaser. Mix an emulsifier with kerosene to move the stain and then clean the kerosene off with emulsifier only mixed with water. With petrol, blot the stain with absorbent towel but do not rub or wipe. The area should then be covered with an absorbent material such as Fullers Earth or Portland cement. Repeat these steps until the stain has gone.
Smoke stains caused by fireplaces can be removed by mixing 500 grams of sugar soap into two litres of hot water and brushing it onto the stain. After the stains disappear scrub with a mixture of detergent and household scouring powder containing sodium hypochlorite.
Removing graffiti from bricks can be done with a commercial paint remover containing methylene dichloride. Pour over the area for a few minutes, scrub to loosen the paint then rinse with water. Then scrub with a scouring powder until the paint has gone.