Wear protective gloves, goggles and clothing to prevent burning or irritation from the chemicals you'll be using.
Mix one part phosphoric acid to six parts water.
Cover fixtures, painted surfaces and concrete that has been colored with oxides to prevent discoloration from the solution.
Apply the solution to the stains using a paintbrush or a spray bottle.
Let the solution sit until the stain fades away. This can take up to 24 hours.
Repeat application after 24 hours if the stain is not completely gone.
Mix a solution of 20 to 40 grams oxalic acid to one liter of water for heavy rust stains.
Apply the solution in the same manner as you would with phosphoric acid but after the stain is removed, neutralize the oxalic acid solution using a mixture of 15 grams sodium bicarbonate to 1 liter of water and do not wash off.
Brush off efflorescence, which is a powdery deposit that often forms on brick materials, using a dry stiff-bristled brush.
Hold a dust pan beneath the brush as you work, or vacuum dislodged bits when you are finished. The salts from the efflorescence must be removed to prevent them from re-entering the brick or other porous material nearby.
Pick up remaining residue using a damp cloth. Do not use a hose to rinse, this will cause the salt to absorb into the material and reappear again after drying.
Mix one part muriatic acid to 15 parts water to clean stubborn efflorescence stains.
Brush on with a stiff bristled brush and rinse with water when the stain is gone.
Saturate the stains with paint remover containing methylene dichloride.
Scrub the area with a stiff brush to loosen the paint and rinse with water.
Scrub remaining paint with a scouring powder until all paint is removed and rinse once more with clean water.
Mix sodium hydroxide and diatomaceous earth into a thick paste to remove stubborn paint stains.
Apply a thick layer and let sit on the stain for at least 24 hours before spraying the area with a hose to rinse the paste off the wall.
Mix 500 grams of sugar soap into 2 liters of hot water.
Apply the solution to the stained surface using a brush until the stain is removed
Scrub the area with detergent and a scouring powder containing sodium hypochlorite.
Mix a solution of one part household bleach to three parts water and a bit of laundry detergent.
Scrub the solution onto the stain using a brush.
Let the mixture set for about 15 minutes and then rinse with clean water.