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

June 21, 2017

Note: Since we wrote this article and made the video, we've introduced Tornado Cleanze, which we now generally recommend instead of Lightning Cleanze for removing black lichen. For best results 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 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 by softwashing:



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

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

If some infestation remains, treat again with Lightning Cleanze.

Finally, treat with Benz Bio Cleanze at 25-30:1. This product will continue the cleaning process over several months while also providing a degree of "residual biocide protection" against recolonisation.

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

Pressure washing and wall render

Important note re pressure washing: Using a power 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 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 followed by a light pressure wash will remove the majority of lichen.

Then Bio Cleanze will 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 as seen in the photos, for which pre-treatment with Lightning Cleanze was 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.

Time and the natural weathering of sun, wind and rain will lift the lichen from the surface once it is dead and it will disappear in 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 and, if necessary, a light power wash on a first clean of paths and patios.

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 12-24 months.

This will usually be sufficient to keep surfaces permanently clean.
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.

Patio slabs badly infested by black lichen before softwashing:


The same patio slabs after lichen has been removed by softwashing:


A badly lichen infested path in which the lichen had grown deeply into the concrete:


The same path after the lichen 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 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 lichen:

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

2)  Treat the area with Lightning Cleanze at 4-5:1 dilution, brushing the chemical into the lichen to help penetration.

3) Rinse and observe the result.

4)  If necessary apply a second treatment of Lightning Cleanze.

5)  Lightly pressure wash any remaining 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).

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 a degree of long-term residual biocide protection against re-colonisation.

7)  When the first signs of algae or lichen growth return, or as a regular 12-18 month regular re-treatment, apply Bio Cleanze at 50:1 (40:1 in cold weather) as an ongoing maintenance plan.

Quick tip: Offering your customers a 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 path, algae will be noticed sometime during the 6-24 months following treatment with Benz Softwash biocides. At this point a quick "spray & go" is all that is required to keep the surfaces immaculately clean and your customer very happy.


We hope this information is helpful.


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

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