How to soft wash a zinc coated (galvanised) roof & zinc flashing

June 23, 2023

How to soft wash a zinc coated (galvanised) roof & zinc flashing

A customer asked if Benz Lightning Cleanze biocide is suitable for cleaning a roof clad in zinc coated sheeting, i.e. galvanised steel? Also zinc flashing?

We told him that galvanised (zinc coated) steel is a material that needs cleaning with care. Like lead it can discolour if not protected by pre and post wetting with fresh water. Zinc can take on a hazy look if not looked after in this manner.

We've never cleaned a galvanised zinc roof with Lightning Cleanze, so cannot comment from experience. However, at 10:1 Lightning Cleanze is not classified as corrosive to metal. So it will probably be ok but could tend to slightly oxidise the zinc.

As always, first treat a test patch to check that your method works on the zinc roofing material you intend to soft wash.

We recommend Benz Bio Cleanze biocide for treating zinc on roofs

The chemical nature of Bio Cleanze enables it to seep between the laps of zinc coated sheets, killing the spores that hide there, better than any other chemical. It's even more effective at getting between the laps than water (because of its lower surface tension).

Quick tip: A light pressure wash will remove most of the surface biofilm and the roof will look reasonably clean. But if not killed with a biocide treatment immediately after being pressure washed, the spores will recolonise and the zinc coated roofing sheets will soon look dirty again.

A single treatment at 30-50:1 is usually sufficient if a zinc roof has been pre-cleaned by pressure washing.

But if not being pressure washed first, and the colonisation is severe, apply two treatments of Bio Cleanze. this will enable the chemical to soak more deeply into the biofilm than is possible with a single treatment.

After treating a galvanised zinc roof with Bio Cleanze, leave it (do not rinse, because you want the chemical to remain between the laps to help prevent future colonisation) and allow natural weathering to complete the cleaning.

Quick tip: The same principles apply to protecting zinc flashing when soft washing the surrounding surface as to protecting lead flashing.

We hope this information is helpful and sincerely wish you great success in your soft washing business,

Benz Team

Click here to get more practical soft washing how-to tips

How to find answers to most soft washing questions: Simply enter a relevant "keyword" or short phrase – e.g. keyword for the above link = "how to" – into our in-site Search Engine (magnifying glass icon on the main menu).

Click here to download our Product Documentation Pack (includes Application & Dilution guides, SDS, PDS, RAMS, PPE & Mask info, COSSH, sample Contract and more)

Order Benz Softwash chemicals & equipment online or by phone:

GB (England, Scotland, Wales)

Phone: 0800 70 74 222 


Ireland and other countries

Phone: 00353 214 622 978


Lines open Monday - Friday, 9am – 5pm

Please note: The above numbers are for orders only (click here for tech support)

PS: Click here to set up your "Clean & Maintain" programme
. After completing an initial soft wash treatment, put your customer on a "Clean & Maintain" ongoing maintenance programme. Your customers will enjoy a permanently clean property and you will enjoy a steady stream of repeat business.

This is clearly a win-win arrangement for you and your customers.


Click here to explore the extensive range of Benz softwash cleaning chemicals & equipment

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

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