Brickwork is readily stained by many agents including plant growth, building materials, paint and just plain grime. Here’s the solution to 3 common brickwork stains.
Plant stains
The most effective way to remove root trails without damaging the brickwork is to dry-scrub with a stiff brush, helped along with a blow torch on low, to encourage suckers to let go. Don’t forget to remove the heat source before scrubbing, especially when working with a nylon brush. You may have some success with low-pressure water washing. This is best used to wash the wall down after the brushing treatment.
If you intend to repaint the wall afterwards with an oil-based coating, use a wire brush for dry-scrubbing, as any stains from the wire will be covered by the paint.
Moss on southern walls
Make up a weak solution of bluestone or copper sulphate, say 200g to 4.5 litres of water, and coat the wall liberally with a broom. You may need to repeat it several times, especially if the wall is freshly painted. Over the period of time, the copper salt will kill the moss growth, and the wall can be hosed clean. The action will take a little time, usually a week or so, but is effective.
The presence of copper sulphate left in the wall will prevent the problem from recurring again for some time.
Mortar stains
While the bricks are being laid, clean off any lumps. Clean off most of the mortar stains with water and vigorous scrubbing about 1 or 2 days after the bricks have been laid. Remove older and more stubborn mortar stains by using a weak 5% to 10% solution of muriatic acid -- that is, one part commercial grade muriatic acid mixed with about fifteen parts water (1:15) -- remembering to add acid to water, not vice versa. Don’t use stronger solutions because they will stain the bricks.
Soak the walls first so the acid will stay on the surface. If the acid soaks into the bricks, it will attack the mortar and, over a period of time, evaporate as acid fumes. Acid fumes will cause metal fittings to corrode, and may cause a problem with sarking and aluminium window fittings. You also need to be careful of using high-pressure water jets, because too high pressure may cause the mortar joints to erode.
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