Softwashing Roofs

Benz Softwash supply softwash chemicals to the professional softwash cleaning trade
We advocate three softwash systems to treat a roof.

Your choice of softwash system will depend on the nature and materials of a particular roof and the requirements of your customer.

Quick Tip: We strongly suggest you position softwashing a roof as a "treatment", not as "roof cleaning". By doing this your customer will be prepared to wait for the full results to show, just like taking a medicine for a body ailment.
Cleaning a roof using soft washing with Benz Blackwash

Above is a roof softwashed with Benz Bio Cleanze

The first softwash system (the one we recommend for most roof cleaning jobs)

Use Benz Bio Cleanze – after manually removing the worst of the growths – for cleaning most roof surfaces. We've found this to be the simplest, safest and most profitable way to clean roofs by softwashing.

Bio Cleanze has the advantage of being able to get deep into the laps by capillary action more effectively than other cleaning products. And, because it does not need rinsing, it is also the most profitable way to softwash roofs.
Bio Cleanze is the perfect product for use in the Benz "Clean & Maintain" softwash systems, which give customers a perpetually clean property and contractors a constant source of repeat business.

The second softwash system

For most roofing materials we recommend treating with Bio Cleanze – and prefer it even for non-porous natural and man-made slate because of the way the product gets deep under the laps and does not require rinsing.

Benz Lightning Cleanze can be used to give a more "rapidly clean" effect when needed. And it can work well on smooth, non-porous roof surfaces such as natural and man-made slate, especially if your customer wants a quick clean (before moving house, for example).

Quick Tip: Bear in mind that when Lightning Cleanze soaks into porous surfaces it can take considerable time to rinse. Rinsing is easy and quick on walls and horizontal surfaces but much more time-consuming on a roof. Remember to factor this time into your pricing if you use Lightning Cleanze on a roof.


Watch this short (0:30) video to see what Benz Lightning Cleanze does to white lichen



A third softwash system

Gently power wash the roof – using a low pressure setting if you have a variable pressure washer. And/or use a fan jet and keep the nozzle some distance from the surface if your power washer does not have a variable pressure control.

Do not use high pressure because this can damage the surface of the roof tiles and significantly reduce their life expectancy.

Work from the apex down (never from the gutters up because of the danger of the high-pressure water spray getting under the tiles).

Note: This is the opposite direction to softwashing with Benz biocides because we want the biocide to get under the laps.

When the roof looks clean, remember that spores will not have been killed, so post-treating with Benz Bio Cleanze will be essential.

How to softwash a roof on a hot day

Whichever softwash system you use to clean a roof, on a very hot day, especially on an elevation facing the Sun, it can be a good idea to first hose down the surface to cool it down. This reduces the possibility of the softwash biocide "boiling-off" before it has a chance to work.

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The importance of rinsing Benz Lightning Cleanze

If you use Lightning Cleanze to clean a roof, always thoroughly rinse it from the surface after allowing 30-60 minutes for the cleaning action to take effect. This ensures the small quantity of salt left behind by the break down of chlorine is removed.

Also, we advise rinsing between applications of Lightning Cleanze to remove the debris cleared from the surface by the first treatment, allowing the next coat to penetrate the biofilm to an even greater depth.

On many jobs only one application is sufficient. But if the colonisation is bad, two treatments – and exceptionally three – may be required.

We also recommend gently brushing each application of Lightning Cleanze into the surface, so that it penetrates the biological growth to the maximum depth and thus increases its effectiveness.

Note: Rinsing Lightning Cleanze thoroughly is particularly important if you are going to post-treat with Bio Cleanze to ensure the surfactant in Lightning Cleanze is removed from the surface.

Treating yellow lichen and moss balls on a roof with Benz Bio Cleanze

Re yellow lichen on roof: It can take 7-12 months for yellow lichen to fully disappear from porous roof tiles. Depending on the local environment and how long the yellow lichen has been allowed to grow into the surface, the timescale may be shorter. On non-porous slate the time-scale time-scale could also be shorter.

Re moss balls on a roof: Any moss balls over 10mm should be scraped if at all possible. Small moss balls will die after treatment with Bio Cleanze and fall into gutter. Bigger than this and it’s down to the roof pitch – the steeper the pitch, the more likely the moss balls will fall off.

If a roof cannot be scraped:

If the moss balls are heavy and/or on a shallow pitch roof, they may stay there and eventually recolonise. Allow up to a year for full results to be seen after treating with Bio Cleanze.

If the moss is still there after 12 months, re-evaluate what to do. If scraping is not an option then treat with Lightning Cleanze at 5:1 (two treatments one after the other can be particularly effective, as the product will soak in more deeply). The moss will turn to white mush after a few hours. The mush should be be sucked up and removed from the site.

This is not the best practice – as the mush can block gutters and downpipes after rinsing (downpipes should be sealed prior to treating) and may contain a certain amount of sodium hypochlorite. This is the reason for sucking up the mush and removing it from the site.

Important note regarding offers of "instant cleaning"

To get the near instant results claimed by some irresponsible contractors requires the application of extremely strong sodium hypochlorite (ie bleach).

We generally recommend using Benz Lightning Cleanze at 5:1 dilution (2% available chlorine), or exceptionately, 4:1 (2.5% available chlorine).

At 5:1 dilution Lightning Cleanze is classified as non-corrosive to metal and rubber fittings. Even at 4:1 it is only mildly corrosive, which can be offset by pre and post rinsing of vulnerable fittings.

But contractors applying raw, industrial sodium hypochlorite at 3-6% available chlorine are spraying a highly corrosive chemical onto their customers roofs.

By doing this they can work faster, then take the money from their naive customers and scarper. They are not interested in building long-term repeat business but only in getting some short-term cash.

Unfortunately this means:

  • They are endangering their own, customers and the general public's health through breathing chlorine fumes and being exposed to a highly toxic chemical that can inflict serious chemical burns.
  • They are endangering the health of animals and children who may stray into the working area.
  • The run-off and overspray will be highly toxic to plant life.
  • Metal and rubber fitting on the roof, guttering and windows fitted into the roof or exposed to spray drift will be damaged.
  • Roofing materials themselves can be permanently discoloured.
  • If run-off is allowed to enter surface drains, which discharge into waterways, it will damage our environment and is illegal.
  • Spraying unapproved sodium hypochlorite for purposes other than its "intended use" (usually disinfecting swimming pools and milking parlours) is also totally illegal.

We are not sure of the impact to a contractors professional liability insurance policy in the event of an accident, or to their customer's household insurance policy, as this will likely vary from company to company. What we are certain of though is the the consequences will not be good ...

In contrast Benz Bio Cleanze and Benz Lightning Cleanze are fully legal and have been approved by the UK government (via the HSE) and Irish government (via the PRCD) for the cleaning of exterior hard surfaces.

So the best way to avoid serious negative consequences is to "Buy Benz and Be Safe".

Evaluate the area to be treated by softwashing and calculate a price for the job

Click here to download a free “Professional Softwash Contractors Pricing Guide, which explains clearly and simply how to calculate the price per area for any given softwashing contract.


Determine how to access the roof


Cleaning a roof with biocide (BENZ Biocidal Wash) using water fed pole
Check to see if all elevations can be sprayed from the ground. If not, use a podium ladder, lightweight tower, cherry picker, or scissors lift.

In this photo Ben is using a conventional window cleaning water-fed pole to deliver Bio Cleanze to clean a badly stained chimney stack.


Walking on roofs

This was standard practice for years before H&S came in. Nowadays best practice is to use a roofing ladder and scaffolding (a tower is often sufficient). If you don't, likely your insurance would be invalid in the event of an accident.

Also, using WFP it's often possible to treat the entire roof without stepping onto the roof at all. The exception can be the need to scrape moss and lichen before treating, although even for this a scraper attached to the end of a pole often works fine.

Determine the extent of moss & lichen growth

Correct evaluation will help you work out the time the job will take, and therefore price correctly.

Protect your customer's plant life

If there’s any danger of serious spray drift, cover your customer’s plants with a lightweight sheet, ensuring that the plants remain undamaged by the covering.

Always spray all plants and lawns in the vincinity of the treatment area, or likely to receive spray drift, with copious quantities of fresh water immediately before and immediately after application of Benz biocides. 

Pre-drenching plant life helps dilute any biocide that may reach the leaves and soil. And post-spraying also washes any spray drift from the leaves and further dilutes any that reached the soil. Pre and post-drenching is a remarkably simple but highly effective way to care for your customers plants, trees and lawns.

Note: In our experience pre and post-drenching with fresh water, and minimising spray drift and run-off with skillful application techniques and Benz Softwash spray nozzles, works just fine. We've found it to be the simplest, least time-consuming and most inexpensive way of protecting your customer's plants. We have found absolutely no need to post-treat your customer's plants with any other product such as a liquid fertiliser (which could be the wrong type of nutrition for your customer's particular plants and therefore could be harmful to them). 

Important general notes about softwashing a roof

  • If there’s a light breeze, angle the spray into the wind to reduce spray drift.
  • Never spray if the wind strength will cause unacceptable drift.
  • Use a projection nozzles only in the rare situations when part of the roof is out of reach of telescopic poles and cannot be sprayed any other way (in our experience this is almost never the case). Avoid moving your pole over unprotected grass or plants when spray is being emitted.

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Setting up your softwashing equipment

Choose an area of hard standing to set up your application equipment. If at all possible do not set up your equipment on unprotected grass. If grass is the only viable option, cover it with a strong tarpaulin first.

Prepare the roof for softwashing

Remove the worst of moss, lichen and liverworts with Benz Roof Moss Scrapers. It’s especially important to remove as much moss as possible from low-pitched roofs situated in sheltered or shady locations.

Watch the video below to learn about Benz roof moss scrapers for removing moss from roofs prior to softwashing with Benz Bio Cleanze

Softwashing application procedure

Use Benz Bio Cleanze at 20-25:1 dilution. This is as strong dilution because the biological growths of roofs tend to be heavy and thick. There is often lichen on roofs, which always requires a strong treatment.

Begin spraying up from the eves, ensuring good penetration into the lap of the tile or slate. Pay particular attention to features such as a dormer back gutter, valleys, and so on as missed spots will start to show regrowth quite soon.

After spraying the whole roof up to the apex, follow with one final treatment down from the apex to ensure complete coverage of the roof.

Btw: The reason for spraying up to the apex, and not down from the apex, is that you can see more clearly where you are spraying.

Also, the slate or tile lap is where there’s the greatest build up of moss and spores. So it’s important to aim the nozzle upwards, thus achieving deep penetration into the lap joint. By spraying up you get more product onto the roof and a more even coverage without the mix running down into the gutters. If you were to spray down, the mix will just run over the lap without getting into the lap.

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Drainage systems

It is important to protect our environment by minimising run-off into sewers and surface drains. Run-off can be kept to minimum or zero by using Benz softwash spray nozzles along with skillful spray and brush control techniques. If some run-off to drains is unavoidable, block the drains and/or gutter downpipes until application has been concluded.

Watch the video below to see how Ben applies Benz Bio Cleanze using a water-fed pole fitted with a Benz softwash spray nozzle


Notes on the video above: On this particular roof, with the ridge running down the hip, Ben wanted to make sure the biocide did not run down the roof tiles and into the gutters.

Obviously all the tiles have to be treated at some point, but if the biocide is running down the roof – and starting to overtake where you are spraying – it's better to stop, treat something else, then go back to where you were spraying and continue from where you left off.

On a standard ridge Ben first cuts in, then does a few courses of tile, then sprays the top of the ridge, then goes back down and sprays a few more courses of tile until it starts running down. Then he works from the bottom up for a few more courses, then back up to the top. (you'll see Ben doing this in the video)

On a roof that has long gutters this process of spray control may not be needed – as by the time you get to one end the other end will be starting to dry.

Spraying techniques like these help keep as much biocide on the roof as possible and prevent it just flowing into the gutters, which is wasteful.

Note: On the roof in the video Ben eventually had nowhere dry left to stand, and did not want to stand on a wet soapy roof, so he sprayed the bottom of the roof from the ground. He could have sprayed the whole roof from the ground, or from a stepladder, but he could not do that and make the video showing how to spray. Always adapt your method to the needs of the individual job.

Before softwashing ...

After soft washing a roof with Benz Pro-Soft Wash biocides


After softwashing

After soft washing a roof with Benz Pro-Soft Wash biocides


Softwashing health & safety

Always wear full PPE (Personal Protective Equipment), including impermeable gloves, hair protection, chemical-resistant clothing and a full face shield.

Barrier off the working area and keep customers, the general public, children and animals away from chemicals and treated surfaces. Only allow them to re-enter when the area has been made safe.

On an area of hard standing, rinse your application and safety equipment with copious amounts of fresh water, being careful not to allow rinse water to flow into flower or vegetable beds, lawns, or surface drains.


Click here to learn more about softwashing roofs via Benz Trade Tips softwashing how-to posts

The Benz Softwash range of softwash cleaning products


Click Here to explore our illustrated softwash cleaning products

Benz Softwash Bio Cleanze DDAC biocide & Benz Softwash Lightning Cleanze SH sodium hypochlorite biocide