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Cleaning – general

Stains and growths can be removed from concrete, although it may be difficult to remove stains completely. Concrete is a porous material so stains and cleaning solutions tend to be absorbed into the surface layers. Concrete is chemically reactive and may dissolve in the cleaning solution. Finally locally applied treatments may alter the texture or colour of exposed ‘as cast’ concrete, causing a local blemish.

Techniques for removing stains without affecting the concrete are based on chemicals that either react with or dissolve the stain. These techniques tend to be slow and inconvenient and may not always eliminate all traces of the stain. All cleaning materials must be used strictly in accordance with the manufacturer’s instructions.

Where the stain has not soaked in too deeply, it may be possible to remove the surface layer of concrete, though this will affect the appearance of the structure.

In some instances it will be appropriate to cover the stains by applying paint or some other coating over the whole surface. This may not be possible with some stains. Whatever coating is applied to the surface, there will obviously be a requirement for future maintenance.

Acknowledgement: The Concrete Society

Other references:British Cement Association, Appearance Matters 5, ‘Removal of stains and growths from concrete’.

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Visual Concrete: Weathering, stains and efflorescence