Algae & Lichen
Algae can cause problems by creating areas of slipperiness underfoot, especially in shady gardens. The primary reason for its appearance is lack of sunlight and air, so if it becomes problematic, it may be possible to lift areas of low growing vegetation, to allow more light into the area.
Pressure washing will remove it temporarily, although ‘soft’ chemicals including soap, bleach or chlorine used as a weak mix will help to clean the growth. Take about 250ml of swimming pool chlorine and mix into a five-litre bucket of warm water.
Standing water sites or areas that do not drain easily may be avoided by increasing the cross fall of a paved area when designing a project.
As always, avoid using chemicals on soft sandstones and limestones.
Lichens are a symbiotic partnership between a fungus and algae, with the dominant partner being fungus, which provides the organism with its shape and fruiting bodies, that appear as mottled areas on paving, especially softer stones such as sandstone.
Some people prefer to see lichen growing on the surface, as it mellows and ages the stone, and when used in association with other reclaimed materials, is appropriate for use in older properties. (See Recycled Paving Materials.)
It is difficult to eradicate, requiring more than one application of fungicide to effectively kill the plant, although a shadow will remain where the ‘roots’ have slightly damaged the surface.
