What are the most effective ways to softwash red algae stains from wall render?

May 15, 2019

Benz Softwash supply softwash chemicals to the professional softwash cleaning trade

We've been asked about the best ways to softwash red algae stains from wall render.

A customer's expectations, their desire for a speedy clean, and the type of colonisation all contribute to a contractor's choice of the best cleaning method to softwash wall render.

What if a customer wants red algae staining rapidly removed from their wall render?

Sometimes a home owner may want to sell their property quickly; or they may have an event planned and want it to look good for their guests.

In such cases the fastest approach to treating the red algae stains is with Benz Lightning Cleanze.

How long will it take for red algae staining to disappear from wall render after softwashing?

Light red algae can usually be treated using the simple "spray & walk away" application procedure of Bio Cleanze. The red algae will disappear from wall render in a few days in warm weather and in only a couple of weeks even in the winter.

Quick tip: This is also true for green and light black algae, mould, etc.

Softwashing red algae from wall render - Case study 1

Red algae, red stain, on brickwork - test area treated with Benz Bio CleanzeIn this photo, you can see how we applied Bio Cleanze at 30:1 dilution to softwash a test area, and only seven days later the brick wall has become perfectly clean.

Quick tip: We advised our customer to contact us to apply a maintenance treatment of Bio Cleanze at the first sign of colonisation (typically 2-5 years on vertical surfaces). We will contact them at the 2-year point to check on the condition of their wall render and, if appropriate, offer them another treatment.

Offering customers an ongoing maintenance programme gives them a permanently clean property and the contractor a reliable source of repeat business.

Why offer customers the Benz "Clean & Maintain" softwash system

Customers are increasingly coming to realise that they need to implement an efficient and effective long-term cleaning and maintenance programme to best look after their property.

More and more people are realising that frequent softwash treatments with Benz Bio Cleanze is an important way of caring for their property, not just a luxury. And they know that they can trust Benz “Clean & Maintain” softwash systems

Very heavy dark red algae staining on wall render can be more problematic

This is because the heavy red algae often has multiple layers of black algae or mould underneath it. These layers of black algae and mould will be exposed as a result of the first treatment. They will need some form of secondary treatment to fully restore the appearance of the property to as good as new.


Soft washing red algae from wall render - Case study 2

In the photo below you can see a heavily red stained render, which will need multiple softwash treatments to restore to its former glory.Red algae, red staining, on wall render before softwashing with Benz Bio Cleanze

There are a couple of ways to achieve this:

1) The easiest and simplest way is to treat with Bio Cleanze, then leave it work with natural weathering for a while; then complete the process with a final treatment of Lightning Cleanze.

Spray Bio Cleanze at 30–40:1 and gently brush into each elevation before moving to the next.

Brushing in Benz Bio Cleanze after spraying red algae, red staining, on wall render.jpgThe brushing is surprisingly quick when the render is still wet from the spray application.

Brushing in helps loosen the surface biofilm, which aids penetration and ensures maximum effectiveness of the treatment.


In the photo below you can see the effect after only two months following a softwash treatment with Bio Cleanze.

The heavy red algae stains have gone but there's some black staining left. A further treatment with Lightning Cleaze will remove this and leave the property completely clean.

Two months after treating heavy red algae, red stains, on wall render with Benz Bio Cleanze

In the photo below you can see the render after being given the final treatment with Lightning Cleanze and having fully dried out.

 Result: A very happy customer!


2) The way to achieve the fastest initial results, but also the most labour intensive, is to first softwash the worst of the red algae stains with Lightning Cleanze at 5:1 dilution.

This is a similar method to that which we describe on our render cleaning page.

Note that very heavy red algae staining may require multiple applications of Lightning Cleanze to get the render fully clean on the day of the job.

How to treat red algae on wall render with Benz Lightning Cleanze

1) Spray the render with Lightning Cleanze at 5:1
2) Rinse
3) Brush in a second application

3 quick tips:

1) Use Lightning Cleanze at 4:1 dilution if test results indicate this to be necessary – but take extra care and use full PPE as it is getting quite strong at that dilution.

In a short time the black stains should be gone with, sometimes, a very light brown “shadow” remaining.

This shadow will usually disappear when the render has dried out. And the action of sunlight and natural weathering over the next couple of weeks will further dissipate it.

2) The red stains often turn pink and will disappear over the course of a few days.

3) For very heavy black staining, treating with Benz Tornado Cleanze may be indicated.

Always follow up with a treatment of Bio Cleanze

It is best practice to follow up a treatment of Lightning Cleanze with a treatment of Bio Cleanze.

  • Remember to first thoroughly rinse Lightning Cleanze from the wall render, before applying Bio Cleanze at 40:1 dilution.


Quick tip: Not post-treating wall render with Bio Cleanze will leave red algae spores deep within the substrate, which will eventually re-colonise the surface.

The chemical nature of Bio Cleanze enables it to soak more deeply into the render than can other products. This deep cleaning effect means that a Bio Cleanze treatment will continue removing any remaining algae through time.

  • It will also impart residual protection against re-colonisation.

Click here to learn more about softwashing wall render on our dedicated render cleaning page

Click here to learn more about softwashing wall render via our Trade Tips posts

We hope this information is helpful.


Ben, Leo & Fiona

Click Here to explore the full range of Benz popular softwash cleaning products

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

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