Identify and remove fungus

How to identify you have fungus

Fungal growth can occur on virtually all surfaces when the "micro-environment" on and around a particular installation is conducive to it. In general, it is believed that fungi can grow as a result of suitable conditions, e.g. the presence of fungal spores, moisture and also of nutrients from "dirt" of various types.

Photograph of a portion of a COLORBOND® steel roof showing heavy fungal growth. All building components may be susceptible to fungal growth if the conditions are right.

Photograph of lichen on a COLORBOND® steel roof. Lichen is a growth incorporating both fungus and algae. Its appearance is quite distinctive.

How to remove fungus

If fungus is suspected, it is recommended that a spot test with sodium hypochlorite solution be carried out for identification purposes. The most convenient source of sodium hypochlorite is household bleach. The bleach should be as fresh as possible and hypochlorite available chlorine concentration should preferably be above 3%. Care should be taken in handling the solution (i.e. wear the appropriate safety equipment-safety glasses, protective gloves etc), which is quite alkaline. Any tested areas should be thoroughly rinsed with fresh water afterwards.

The test procedure is basically to apply a drop of the bleach solution to a suspected area, mark the extent of the drop (unobtrusively) and wait a few minutes. If fungus is present, the dark material will be destroyed by the bleach and a clean drop area will result.

Please note: this is not a foolproof test for identifying fungus as the bleach can also affect organisms such as algae and bleachable organic matter. However, it is a valuable test as it will distinguish between fungus and normal inorganic dirt, which will not be bleached.

To restore a roof affected by fungus, it is recommended that the roof be washed down with a 2% sodium hypochlorite solution. The sodium hypochlorite solution can be made up from commercially available bleaches.

To assist in making up the solution, Table 1 below shows the dilution required for different strength bleaches to give a 2% solution. The bleach should be applied with a soft bristle broom, left for 3-5 minutes, and washed off with copious amounts of water. A small amount of household detergent may be added to the bleach if necessary to improve wetting.


If you collect rainwater from your roof, it is recommended the line between your gutters and the collection tank be disconnected before commencing cleaning to avoid contamination of the water supply.

The use of commercially available fungicides is not recommended as they may be detrimental to the long term performance of COLORBOND® steel.

Table 1: Sodium Hypochlorite Solution Dilution Guide

% Sodium hypochlorite or
% available chlorine in bleach (
by weight) (NB: 10g/L = 1%)

Dilution to give 1L of 2%
sodiumhypochlorite solution






200mL bleach + 800mL water

400mL bleach + 600 mL water

500mL bleach + 500mL water

670mL bleach + 330mL water

No dilution required

This information is intended as a guide only. For more information, please see Technical Bulletin TB 27 - Identification of Fungus in the field and Recommendations for its Removal.