What are the unique problems associated with softwashing man-made roof slates? (Part One) (video how-to)

February 01, 2017 4 Comments

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

We need to be cautious when softwashing man-made roofing slates.

Man-made roof slates often lose their coating over time, through natural weathering.

Cleaning the "biofilm" from roof slates may expose the fibre cement or other material the slate is made from, which, before softwashing, will have been covered over by organic growths.

Although the roofing slate may be structurally sound, the coating may not be. And this will become evident after the man-made tiles have been given a softwash treatment. So we need to make our customer aware of this possibility before we begin the softwash treatment.

The test patch in the photos below shows what can happen to very old slates
How to clean man-made roof tiles by soft washing
How to clean man-made roof tiles by soft washing
The photos below show man made slates that are only seven years old, proving that the coating on relatively new coated slates can also fail quickly.The roof was eventually re-painted by the manufacturer of the slates, as they carried a ten-year colour guarantee. The roof was not softwashed or pressure washed.
How to clean man-made roof tiles by soft washing
How to clean man-made roof tiles by soft washing
How to clean man-made roof tiles by soft washing
Organic growths can also damage a roof coating. The 17 second video below shows how the growths can bind with the coating, which in turn can damage the coating.
We recommend treating man-made roof slates with Benz Bio Cleanze, after manually removing the worst of the moss and lichen.

Bio Cleanze will "creep" up inside the laps better than other cleaning products, ensuring all the growths and spores are killed. In our experience this is the best way to give a softwash treatment to clean man-made roof slates.

Important: Always treat an out of the way test patch first and look for the tell-tale pitting of the tile coating before treating or cleaning the whole roof. Always obtain your customer's agreement that the results are acceptable and get their permission to treat the remaining roof surface.

We hope this information is helpful and inspires you to succeed in your softwashing business.

4 Responses


July 31, 2017

Hi Sidney

My same comments as for your previous question apply because there are so many permutations of material involved in manufacturing man-made slates.

You could also consider treating with Benz Biocidal Wash, which should do the job without harming anything. The downside is that it can take several months to show full results and you’ll need to educate your customer to be patient while waiting to see the full effects of your work.

The rule is to treat a small test area of any surface you are not sure of before beginning full treatment. That’s the only way to know for sure if a soft wash chemical is going to be safe for a given surface.

Regarding sealing: If you rinse the roof thoroughly after treating with either Benz Blackwash or Benz Biocidal Wash there should not be a problem. To be absolutely certain you should check with the manufacturer of the sealer you want to use if there could be any possible negative implications. Send them our SDS sheets and let them know the surface will be rinsed prior to applying the sealer.

sidney murtagh
sidney murtagh

July 27, 2017

hi leo i want to spray blackwash on to a chimney to removed red algae will the run off take the coating of man made slats


May 11, 2017

Hi Sidney,

Thanks for your question. We cannot comment on all man-made slats as the materials can differ from roof to roof. The rule of thumb is always clean a small, obscure test patch first and look for the tell-tale pitting of the tile coating before treating or cleaning the whole roof. Always obtain your customer’s agreement that the results of the test patch are acceptable and get their permission to continue treatment of the remaining roof surface.

Regards sealers, we are testing a sealer now and, if all goes well, will be offering this asap. In the meantime, if you think a surface needs sealing be sure to use a breathable sealer, preferably water-based. Our observations and experience suggests that non-breathable sealers or those that put a thick coating on a surface should be avoided. The sealers we prefer soak into the surface, preventing the ingress of water, without changing the appearance of the surface.

I hope this helps, Leo

sidney murtagh
sidney murtagh

May 04, 2017

hi ben will all man made slats go white if treated with biocides just clean down a roof now im wondered what to do next need to seal roof after cleaning. thank. sid murtagh

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