Soft washing render: painted, pre-paint prep & painting

June 08, 2022

Soft washing painted, painting, pre-painting render

We primarily recommend using Benz Lightning Cleanze biocide for preparing surfaces, including painted surfaces, ready for painting.

Any algae, etc, living on the painted surface will be instantly killed, then rinsed off along with cobwebs and other debris and contaminants, leaving a sterile surface ready for painting or repainting.

If it is STO render then it may not become perfectly clean without steaming; but it should be clean enough to paint over. Careful observation of a small test area will determine this.

Sand & cement render requires a different approach. Click here to learn how to soft wash sand & cement render

Is Lightning Cleanze safe for using on paintwork?

We sell Lightning Cleanze to professional painters for pre-cleaning surfaces prior to painting, and have received no reports of damage to paintwork or other problems.

Plus, our own extensive testing and experience of treating thousands of properties since 2013 has also resulted in zero damage to paintwork.

Lightning Cleanze is easy and quick to rinse, and has never been the cause of any failure of a paint system.

Click here to learn more about Benz Lightning Cleanze softwash biocide, which kills and removes biological growths and spores such as algae, lichen, moss and mould.


What if your customer says their paintwork needs repainting after it's been soft washed?

Not only do Lightning Cleanze and Bio Cleanze not damage paintwork, they are used by professional painters to clean and prepare a surface, including existing paintwork, ready for painting.

What can happen is that when old paintwork is cleaned, what was under the dirty paintwork becomes exposed. It's important to realise, and explain to your customers, that any damage that is then seen was already there, and soft washing has simply made it visible.

It's always a good idea to inform customers before any soft washing job, on any surface, that pre-existing damage may be made visible. When they are forewarned and understand, most customers will not be unduly concerned.

It's also a good idea to take close-up before photos, which you can refer back to should a customer not believe that the damage already existed.

How to clean painted through-colour render

Sometimes you will come across through-colour silicone wall render that's already been painted. Be careful to check the surface, and ask your customer what's been done, before giving a soft wash treatment.

Painted through-colour render is rare. The give-away is that paint will often be peeling off, which is why it’s not a great idea to paint it in the first place.

Through-colour silicone render needs careful pre-paint preparation and treatment with Benz Lightning Cleanze biocide and/or Benz Bio Cleanze biocide, to prevent algae growing under the paint.

Quick tip: Through-colour render such as Krend must be painted with a specialised paint designed specifically for repainting through-colour render.

KRend's recommended paint supplier is a company called "Rendit". Phone 0130 288 4385. They specialise in render paints and can match KRend colours. These are the people to recommend to your customer if they want to paint their through-colour render.

Click here to learn more about painting through-colour render

Pre-cleaning render with Benz Bio Cleanze

If your customer objects to your using a "chlorine" product, even one as safe as Lightning Cleanze, you can pre-clean their through-colour render with Benz Bio Cleanze biocide.

Once dry, Bio Cleanze can be painted over but the biofilm still needs to be washed away.

After one month most of the biofilm will have gone through the natural weathering effects of sun, rain and wind. But rinsing prior to painting is still a sensible action to remove any loose debris, dust, spiders nests, etc. 

Results from a Bio Cleanze soft wash treatment will vary depending on:

  • The local environment
  • The time of year (Bio Cleanze works faster in warm weather)
  • The amount of sunshine and rain each part of the surface gets
  • The depth of colonisation
  • The time that colonisation has been allowed to grow into the surface. 

It's impossible to give an exact time for results to be seen when using Bio Cleanze. It could take a few days or several months depending on the nature of the colonisation and the factors outlined above.

Quick tip: In general, Bio Cleanze comes into it's own on porous surfaces, when it's powerful "wetting" properties allow it to soak deep into the substrate, killing deeply rooted growths and spores, while offering residual protection against re-colonisation.

None of this is possible on a non-porous painted surfaces, for which we usually use Lightning Cleanze, suppported as required by Benz Tornado Cleanze.

Learn more about soft washing render:

Quick tip:
 Some painted render, if it was not properly prepared by pre-paint cleaning with Lightning Cleanze or Bio Cleanze biocides, may have algae, etc, growing under the surface. This may only be fully visible when the surface colonisation has been killed and removed.

Not much can be done about this, other than stripping the paint and treating the algae growth prior to repainting.

This is why it's important to clearly explain the situation to your customers in advance of giving a treatment. When they understand the situation and possible results, they'll hold you blameless if some dark patches under the painted surface remain.

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

Ben, Leo, Fiona, Stevie & Anthony

Click here to get more practical how-to tips about soft washing painted surfaces

How to find answers to most soft washing questions: Simply enter a relevant "keyword" or short phrase – e.g. keyword for the above link = "paint" – 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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