How to remove lichen (including "black spot") from concrete, brick, render & tiles

June 21, 2017 4 Comments

Note: Since we made the video, we've introduced Tornado Cleanze, which we now generally recommend instead of Lightning Cleanze for removing black lichen. For best results – and to impart residual protection against re-colonisation – give a final treatment with Bio Cleanze.

Benz Softwash supply softwash chemicals to the professional softwash cleaning trade

Several customers asked us for our suggestions as to the best way to remove lichen (including "black spot" which is black lichen) by softwashing.

Lichen are white, brown, yellow and black (i.e. "black spot") growths that grow on slate and concrete tiled roofs, as well as on concrete paths, monoblock drives, brickwork and occasionally on wall render.

Lichen can be very tough to remove and pressure washing alone is rarely effective.

Start by watching this video to get a brief overview of, and basic insights into, the best way to remove lichen (including "black spot") by softwashing:



Lichen (including black lichen, or "black spot") attach themselves to, and actually grow into, the surfaces of roofs, paths and walls

The best way we've found to remove lichen is to first kill it by treating with Benz Tornado Cleanze, neat or diluted up to 50%. 

Or, treat with Benz Lightning Cleanze diluted at 4-5:1 (dilute according to the severity of infestation and the results of your test patch).

Follow this treatment with a light pressure/jet wash, working the dead lichen spots with the jet to free them from the surface.

If some infestation remains, repeat the treatment.

Finally, treat with Benz Bio Cleanze at 25-30:1. This will continue to deep clean over several months, killing any remaining spores, while also providing residual protection against recolonisation.

Important safety tip: If children or animals will walk on the treated surface, apply Bio Cleanze at only 50:1, keeping them well away from the working area and allow the surface to become completely dry before allowing them back.

Pressure (aka jet/power) washing and wall render

Important note re pressure washing: Using a pressure/power/jet washer on lichen without first killing it with Lightning Cleanze or Tornado Cleanze – which means the growths will still be well rooted into the surface –  may do more harm than good.

The pressure will rip the roots out of the surface, potentially damaging it.

But when first killed with Lightning Cleanze or Tornado Cleanze the roots will come out much more easily.

Important note re wall render: When treating render we generally do not recommend high-pressure jet washing, as it can damage the delicate surface of some modern renders such as KRend and Weber.

Use of a jet washer, set to low pressure and/or using a wide angle fan jet, is fine for rinsing however. The pressure of the water when it contacts the render should be approximately that of tap water pressure.


The combination of Lightning Cleanze or Tornado Cleanze followed by a light pressure wash will remove the majority of lichen.

Then Bio Cleanze will then work through time – from 6 weeks to 12 months – to remove any remaining lichen and kill any remaining spores deep into the surface.

The actual time it takes Bio Cleanze to work will depend on factors such as:

  • The local environment
  • Level of infestation
  • How long the infestation has been allowed to grow into the surface
  • Prevailing weather


Quick tip: Treating lichen with Bio Cleanze only will also kill a lot of lichen (the exception being very heavy black lichen infestation such as seen in the photos, for which pre-treatment with Lightning Cleanze or Tornado Cleanze is highly beneficial).
If using Bio Cleanze as a stand-alone treatment we recommend the lichen is given two strong treatments (20-25:1) to ensure the deepest penetration. Returning in 1-2 months to give a follow-up treatment may also be indicated, depending on the severity of infestation. Brushing in with a stiff brush is also beneficial.

Time and the natural weathering of sun, wind and rain will usually lift the lichen from the surface once it is dead and it will disappear within a year.

If a customer trusts the contractor and is willing to wait for results, this can be a highly effective way of removing lichen and one that we advocate for softwashing roofs whenever possible.

However, many customers want to see immediate results, hence one of the reasons we suggest using Lightning Cleanze or, preferably, Tornado Cleanze and, if necessary, a very light jet/power wash for the first clean of paths and patios. Ongoing a treatment with Bio Cleanze will be sufficient to keep them permanently clean without further need for jet washing.

Enrol your customers onto your ongoing softwash maintenance programme

On subsequent maintenance visits, clear loose organic material with a light jet wash, then give a "spray and go" treatment of Bio Cleanze (diluted 40-50:1) every 6-24 months. The time interval varies according to multiple factors such as the materials treated, the local environment and weather conditions, and how well your customer keeps their property clear of organic matter.

Regular treatments with Bio Cleanze will usually be sufficient to keep surfaces permanently clean all year around.
Click here to learn how to set up a "Clean & Maintain" ongoing maintenance programme


We've found this multiple treatment approach to be especially powerful for cleaning deeply ingrained lichen, as in the photos below of extremely bad black spot infestation.

Patio slabs badly infested by black lichen ("black spot") before softwashing:


The same patio slabs after black lichen ("black spot") has been removed by soft washing:


A path badly infested with black lichen ("black spot") and black algae in which the black lichen had grown deeply into the concrete slabs:


The same path after the black lichen / black spot and black algae has been removed by softwashing: 

Quick tip: The pressure washer we used to achieve the above results was only a small domestic jet washer. It was the cheapest one available and we used it as an experiment to prove that it's not necessary to invest vast sums of money in complex, expensive equipment when first starting out softwashing.

We've found the following sequence to be a highly effective way to remove black and white lichen:

1)  Hose down, or lightly pressure wash, the surface to remove loose organic matter.

2)  Treat with Tornado Cleanze, neat or diluted up to 50%. Or treat the area with Lightning Cleanze at 4-5:1 dilution, brushing the chemical into the lichen to help penetration (multiple treatments can be beneficial for badly infested surfaces).

3) Rinse and observe the results.

4)  If necessary apply repeat treatments of Lightning Cleanze or Tornado Cleanze.

5)  Lightly pressure wash any remaining black lichen, which will now be dead and its roots will more easily lift from the surface. (even a domestic pressure washer will do the job after a softwash treatment, as we have proved).

6) Apply Bio Cleanze at 25-30:1. This will find its way deep into the surface, clean out any remaining lichen spores, and provide long-term residual biocide protection against re-colonisation.

7)  When the first signs of algae or lichen growth return, or as a regular 6-24 month regular re-treatment, it is usually sufficient to apply Bio Cleanze at 50:1 (40:1 in cold weather) as an ongoing maintenance plan.

Quick tip: Offering your customers a "Clean & Maintain" ongoing maintenance plan will give them a perpetually clean property and will give you a continual stream of lucrative repeat softwash business.

Lichen usually takes a long time, even years, to return but sometimes, in damp, shaded areas of paths and patios, algae will be noticed sometime during the 6-24 months following treatment with Benz Softwash biocides.

At this point a quick "spray & go" with Bio Cleanze is all that is required to keep the surfaces immaculately clean and your customer very happy.

Click here to learn about our free online softwash training

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Click here to visit our softwashing how-to YouTube channel

Benz soft washing how-to videos cover every aspect of soft washing. We show you how to soft wash domestic and commercial roofs, paths and drives, tarmac, concrete, walls, wall render (including KRend, Monocouche, Weber), wet pour safety surfaces, tennis courts, car parks, wood decking, fences, sheds and more ...

Our sincere wishes for a good life and a profitable business,

Ben, Leo & Fiona


Click here to explore the full range of Benz popular softwash cleaning products
Benz Softwash Bio Cleanze DDAC biocide & Benz Softwash Lightning Cleanze SH sodium hypochlorite biocide

4 Responses


November 12, 2018

Hey Keiron,

Thanks for letting us know. That’s not a use we’ve heard of before and great to add it to the list of uses Benz Lightning Cleanze can help with.



Keiron Bradley
Keiron Bradley

November 12, 2018

Guys, thought you might be interested to know that I recently treated some tannin stains on render with Blackwash and it significantly reduced staining. It had leaked from wooden trellis on to newly rendered walls so after trying a small test patch I just sprayed it on, left for half an hour, rinsed and repeat.
Gave it several treatments without any agitation and stain was still faint but much better than it was, and the owner was well pleased.


June 24, 2017

Thanks Andrew!

andrew marling
andrew marling

June 21, 2017

Great informative videos.

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