Soft washing a roof from algae, lichen, moss & mould

The unsightly red, green or black staining you see on a roof usually comes from algae, lichen, fungi, moss or mould – or a combination of them.

Algae, lichen, fungi, moss and mould can begin to appear on a new roof after around 2–7 years. Exactly how long this takes depends on the surrounding environment and prevailing weather.

Lichen on roofs

Lichen appears as round white, brown or black spots. You will often see it on slate and concrete tiled roofs.

Lichen attaches itself firmly to the roof surface, which is why power washing often fails to remove it.

The most effective way to deal with lichen is to kill it and allow the dead growth to gradually release itself from the surface.

This can take anywhere from a few weeks to several months depending on the degree of colonisation and the local environment.

Where lichen colonisation is particularly heavy, a second application of Bio Cleanze after around one month can speed up the process.

Moss on roofs

Moss often grows in the joints between roof tiles.

This can interfere with drainage and allow water into areas where tiles overlap.

Moss holds water and adds weight to a roof. When this water freezes, it expands and can damage tiles and gutters.

Even relatively small amounts of moss can reduce the full drainage capacity of a roof.

Moss will often begin to appear around a property after 2–7 years and particularly likes concrete roof tiles.

On many buildings, moss starts growing on the roof before spreading into the gutters and eventually onto paths and driveways.

Keeping a roof clear of excessive moss helps protect the property from the damaging effects of uncontrolled moss growth.

Preparing a roof for soft washing

Remove established moss and other heavy growth by manually scraping the roof before treatment.

Many roofs only get cleaned once the moss build-up has become severe, so this stage is important.

If the roof pitch is suitable and the tiles are sound, a trained and competent roofer may be able to carry out the work directly from the roof.

Where the roof is too steep or fragile to walk on, you can carry out scraping and spraying from the ground or another safe working position using equipment based on water-fed pole technology.

Protect gutter outlets before you begin to stop moss and other debris from blocking the downpipes.

You can also lay tarpaulins around the perimeter of the property to catch falling moss and debris.

Protecting plants

Run-off and overspray from Bio Cleanze and Lightning Cleanze can discolour leaves and flowers.

Thoroughly drench vulnerable plant life with fresh water immediately before treating the roof and rinse it again afterwards.

This simple process provides effective protection against accidental overspray.

Click here to learn more about protecting your customer's plant life when soft washing

What about solar panels?

Whenever possible, treat the roof before solar panels are fitted.

Once panels are installed, it can become almost impossible to remove biological growth living directly underneath them.

Treating the roof beforehand with a strong working dilution of Bio Cleanze gives you access to the whole roof surface before the panels restrict access.

Can you treat a moss and lichen-covered roof with Bio Cleanze alone?

Bio Cleanze treats the biofilm on the roof rather than removing heavy moss itself.

First remove established moss manually using Benz professional roof moss scrapers.

After scraping, apply Bio Cleanze at approximately 25:1 to treat the remaining biofilm and biological growth.

How long the treatment takes to show its full results depends on the local environment, prevailing weather and roof pitch.

The steeper the roof pitch, the greater the natural self-cleaning action from sun, wind and rain.

These natural weathering processes gradually remove the remaining dead lichen and biological growth.

The cleaning action of Bio Cleanze continues for many months after treatment. On porous surfaces it can also provide a degree of ongoing protection against re-colonisation.

Quick tip: Explain the progressive cleaning action of Bio Cleanze to your customer before starting the job. This is an unusual characteristic of a cleaning chemical, and customers need to understand that the roof will continue to improve after you leave.

Soft washing equipment for roof cleaning

You can use a window cleaner's water-fed pole to gently brush treatment across a roof while avoiding ladders on many properties.

Low-pressure application systems with telescopic poles allow you to reach large areas while working from the ground or from suitable scaffolding.

Use a coarse spray made up of relatively large droplets wherever possible. This helps minimise spray drift.

Quick tip: Roof soft washing can make a profitable additional service for roofing contractors who already have the equipment, knowledge and skills needed for working safely at height.

How long does a softwash roof treatment last?

Several factors influence how quickly biological growth returns.

• Exposure to sunlight
• Nearby trees
• Humidity
• The porosity of the roof tiles
• The condition and surface texture of the tiles

If someone has previously power washed the roof, they may have altered the porosity and surface characteristics of the tiles.

Biological growth can then return more quickly and, in severe cases, it may not be possible to completely restore the original appearance of the tiles.

Most roofs will remain clean for around three years before biological regrowth makes another treatment necessary.

Concrete tiled roofs can often stay clean for longer before visible regrowth appears.

Restoring and cleaning old roofs

Some people see moss, lichen and algae on an old roof as part of the character of the building.

But biological growth can damage the roof structure if you allow it to develop unchecked.

Bio Cleanze allows you to gently clean and restore old roofs without using the aggressive action of high-pressure washing.

Apply Bio Cleanze evenly across the roof surface.

If you need to brush the treatment across the surface, do so gently and carefully.

The biofilm will die without aggressive mechanical cleaning.

Quick tip: Where you find severe black lichen colonisation, applying a strong working solution of Lightning Cleanze before treating with Bio Cleanze can be an effective approach.

Non-aggressive soft washing allows you to clean old slate and tiled roofs without subjecting the surface to the potentially damaging force of high-pressure washing.

What if the property also has sandstone?

Older properties sometimes have sandstone walls supporting or surrounding the roof.

If your customer asks you to clean these at the same time, remember that sandstone is relatively soft and needs particular care.

Benz biocide products allow you to treat sandstone without the aggressive cleaning action that can damage the surface.

Health & safety

Always assess the site for Health & Safety considerations before starting work and establish a safe working method.

Wear appropriate PPE when handling and applying softwash chemicals.

Wash exposed skin thoroughly with fresh water before eating, drinking or smoking and again when you finish the job.

Never compromise safe working practices when carrying out roof cleaning or working at height.

We hope this information helps you achieve great results and continued success in your soft washing business.

The Benz team

Click here to explore the full range of Benz softwash cleaning chemicals and equipment