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Moss, lichens, algae and other growths are often associated with concrete that has a high moisture content. Growths are not normally deleterious to concrete. In circumstances where they are considered undesirable a toxic wash (containing bleach or proprietary chemicals) may be used. Thick growths should be scraped off prior to the application of the wash. Some toxic washes leave a residue that discourages subsequent growth, though this is unlikely to last for more than a couple of years. Alternatively the surface may be treated with a water-repellent coating, which should reduce the likelihood of further growth for several years.
Alternatively, growths may be removed by using high-pressure water cleaners. Moulds etc forming on internal surfaces indicate consistently damp conditions. To affect a permanent cure it will be necessary to eliminate the cause of the damp.
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Acknowledgement: The Concrete Society
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