When should you tell customers about shadow ("ghost") staining?

May 03, 2022

Shadow stain remaining after soft washing

When deep staining from algae, etc has been allowed to remain untreated for a considerable time, some light shadows may remain visible even after giving the surface a thorough soft wash treatment.

That's just the way it is. And there's nothing anyone can do about it.

But if a contractor tries to explain this shadow, or "ghost", effect to their customer after doing the work, their customer may well think he's trying to pull the wool over their eyes and is making excuses for poor workmanship.

Fortunately there's an easy solution that keeps everyone happy. 

Simply explain the reality of the situation to customers in advance, before starting work.

When a contractor clearly explains in advance of treating their property what can realistically be achieved, and explains the reasons why, their customer will be prepared for, and accepting of, the final results.

The reasons for shadow staining

“Ghosting" – seeing the outline of underlying bricks or blocks through a coating of render, will almost certainly be the result of poorly applied render.

The render will likely not be sufficiently thick, or one of the stages of application may have been missed or done badly. For example, a sand and cement render, and some through-colour renders, have a "scratch coat" that is applied over the blockwork first to provide a foundation. The final finish is applied on top of the scratch coat. 

If the scratch coat is applied too thin, the lines of the blockwork will be visible. This effect is often seen on boundary walls,  possibly because often not as much care is taken when applying render to them as when rendering a house.

Also, if the wall is heavily colonised, when that colonisation is treated and removed the underlying "ghost" outline of the blockwork – which was partially obscured by the colonisation – becomes clearly visible.

Quick tips: 

  1. For heavily colonised walls consider treating with Benz Tornado Cleanze. We created it for this type of job and is particularly useful for treating capping stones. It is essential to treat capping stones thoroughly because spores hide in joints and crevices and, if not treated, will quickly re-colonise the rest of the wall.
  2. If black algae has been allowed to grow into the surface for a long time without treatment, the residual "shadow" stain may not be possible to shift completely.
  3. Shadow staining is usually caused by acids from biological growths – in particular red algae.
  4. If the colonisation is particularly bad we suggest, following a pre-treatment with Benz Lightning Cleanze and/or Tornado Cleanze, treating with Benz Bio Cleanze at, say, 20-30:1 and will soak deeply into the render, clean and protecting through time for up to a year.

Why treat render with Benz Tornado Cleanze?

  1. Tornado Cleanze is a thick gel and so offers the benefits of a long contact time. This long contact time, along with the formula offering 5% available chlorine and a highly effective surfactant, gives it greater surface cleaning power than any other product we know of.

    It is even stronger than Benz Lightning Cleanze, which itself has a more effective surfactant than anything else on the market we've been able to find even after years of trial and error testing.
  2. Apply Tornado Cleanze liberally, leaving a thin film on the surface. Agitate after 15 minutes. And if the colonisation is really bad, leave for a full 60 minutes activation time before thoroughly rinsing.
  3. Click here to visit the Tornado Cleanze product page which contains more detailed information about the product and the best application practices.


What's the practical value of clear communication?

The most important benefit of clear communication – as outlined at the beginning of this Trade Tips post – for you as a contractor, is a happy customer who will refer you to their friends, neighbours, family and work colleagues.

And they will be more likely to want to become your repeat customer and be put on your "Clean & Maintain" ongoing maintenance programme.


Click here to get more practical how-to tips for soft wash stain removal 

Quick tip: Enter a relevant "keyword" or short phrase into our in-site Search Engine to find answers to most of your softwashing questions (e.g. keyword for above link = "stain")


You can order Benz Softwash chemicals & equipment online or by phone:

GB (England, Scotland, Wales)

Phone: 0800 70 74 222 

Online: www.benzsoftwash.co.uk

Ireland and other countries

Phone: 00353 214 622 978

Online: www.benzsoftwash.com

Lines open Monday - Friday, 9am – 5pm

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

We sincerely wish you great success in your soft washing business, 

Ben, Leo, Fiona, Stevie & Anthony


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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