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Call us on (02) 9986 2126
Roof Cleaning Information

Roof Cleaning Information

Removing biological growth from your roof is easy. There are 2 main types of growth that can be found on a roof: lichen and black mould.

How to identify lichen and black mould:

Lichen often appears as a flat cauliflower-like growth, sometimes seen on rocks and logs out in the bush. Lichen is often a light green-grey colour. Lichen is difficult to remove manually as it has many natural suction-caps that anchor it to the surface it is on.


Black mould is best described as dirt that does not move. Black mould will be a very dark colour, mainly black or grey, and looks like specks of dirt however they will not come off when washed. Bleach based products can make it appear to be gone however, the mould can return quickly. Wet & Forget does not contain bleach and is specifically designed to target and kill the biological growth which keeps the surface cleaner for longer.

Treating roof growth:

We have two products that will effectively kill and decompose biological growth on roofs. These two products work the same way, however the visual results are not instant and these products will take some time to decompose the dead growth.

  • Black mould will noticeably improve within 6-8 months, however if the area is heavily contaminated it can take up to 12 months.
  • Lichen requires two applications within 15 minutes of each other and will take 8-12 months to decompose.

Wet & Forget 5L Concentrate

The original Wet & Forget 5L concentrate makes 30L of product when diluted into a garden sprayer and can cover a minimum of 100sq metres, depending on the porosity of the surface. When Wet & Forget is applied it immediately kills the spores, and then works with the weather to decompose the growth over time.

Learn more about Wet & Forget here

Rapid Application 2L Hose-End

The Rapid Application 2L Hose-End does the exact same job as the Wet & Forget 5L concentrate, the only difference is that it has been designed to be quicker and easier to use (which is why it is in a 2L bottle) and it connects to a standard garden hose. Rapid Application dilutes automatically in the bottle and will also make 30L of product and cover a minimum of 100sq metres.

Learn more about Rapid Application here


These two products, while they do the same thing, are NOT interchangeable! Wet & Forget cannot be used in the Rapid Application bottle. Learn more about that here.

Treating Lichen and Black mould with Wet & Forget OR Rapid Application

Treating Lichen

For an average 3 bedroom tile roof (approx. 150sq metres) with lichen, you will require either 3 x 5L Wet & Forget concentrate bottles or 3 x 2L Rapid Application bottles. This depends on how much of the area is covered with lichen and how porous the surface is. Lichen should be spot sprayed first and left for 10-15 minutes before treating the entire roof. After 10-15 minutes, respray the lichen and then spray the rest of the roof to the point of saturation.

This ensures that the lichen properly absorbs the product – the first application dissolves the waxy coating of the lichen, and the second is to penetrate it and kill the spores.

Treating Black Mould 

For an average 3 bedroom tile roof (approx. 150sq metres) with black mould, you will require either 2 x 5L Wet & Forget concentrate bottles or 2 x 2L Rapid Application bottles. Due to the undulations in the tile, the area being treated is actually larger than 150sq metres, and this is why we say to use 2 packs. This also depends on how much of the area is covered with biological growth and how porous the surface is.

How and When to treat your roof:

Wet & Forget and Rapid Application are best applied to a DRY roof on a cool, dry day with minimal wind. This will avoid the product being blown away as it is being sprayed on and will also avoid it evaporating too fast in the hot sun or on a hot surface. Make sure that there is no rain expected for at least 12 hours, as premature rain can wash the product off before it has properly penetrated the growth. If these conditions have been met, it is a good time to apply Wet & Forget or Rapid Application! Spray the product on the affected surface to the point of saturation. DO NOT rinse it off! If the surface you are treating is badly contaminated, you can apply a second application one month after the first.

Notes about Tank Water

If you are on tank water disconnect the water supply to your tank for at least the first 10mm of rain or 2 good downpours to avoid any chance of contamination. Check before reconnecting that the water flowing onto the ground, when raining is not foaming.

Safety Information

Please ensure when applying Wet & Forget or Rapid Application that the instructions are followed properly and that the correct PPE according to the back label is worn. Wet & Forget should not be applied to your roof without the use proper safety equipment. Avoid standing on areas that have already been treated as the area will be slippery until the product is dry.

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