Lichens (pronounced LY-kens not litchens) are slow growing fungi and are actually a good indicator of a healthy environment.
Lichen and moss can grow on roof tiles but this does not indicate a deterioration of the tiles, nor will it affect the performance of tiles.
Lichens are unlikely to make any significant difference to water absorption through the tile, even though they obviously can hold more water against the tile for a longer period.
Lichens and moss can be removed by:
- High Pressure Cleaner – You can hire a medium to high pressure cleaner to remove lichens and moss but be careful that you do not blast holes in the valley flashing or gutters if they are rusty. Also take care not to damage the mortar or tiles as they can become brittle over time.
- Stiff Bristle Broom or brush
- Copper Sulphate (bluestone) – Can be purchased from your local hardware store. Two kilograms should treat an average house; or
- Household detergent or bleach. Note: While lichens may succumb to household bleach or detergent, there is no long-term eradication effect.
Step 1 – Remove all dirt, moss, lichen, mould and all other surface contaminants by detergent (or bleach) washing and using a stiff bristle broom or brush.
Step 1 – 2kgs of copper sulphate to 45 litres of water should treat an average house. Follow the manufactures instructions to remove the lichens and mould.
Note: The bleach and copper sulphate will corrode the coating on gutters. This can be minimised by running water through the gutters during the operation, but light corrosion could occur as the growths may retain some corrosive solution whilst dying and dispersing.
It is important that in both cases, you the disconnect gutters from any rainwater tanks until after the first rainfall to avoid possible poisoning.
Be careful that while cleaning the tiles you do not crack them.
A Guide to Removing Lichen And Moss On Roof Tiles,