Red algae staining on walls is a common problem throughout modern construction. The best and easiest way to remove red algae from exterior walls is by using specialist chemical biocide cleaners and low pressure rinsing. Depending on the type of chemical cleaner used, the algae will be gone within a few hours or a couple of weeks by following the steps below.

Quick Steps:

  1. Identify what type of contaminant is present
  2. Choose the chemical most appropriate for the building
  3. Apply the chemical at low pressure and repeat as needed
  4. Rinse the walls with fresh water to remove any chemical residue
  5. Stand back and look at your sparkling walls!

Why has my wall gone red with algae?

There was a time when most residential homes were built out of brick. As more modern surfaces finishes have been developed, the construction industry now favours coloured renders.

These render coatings produced by the likes of K-rend, Monocouche and Parex often have a very porous texture which allows for the capture and holding of water droplets for a much longer time than the smooth impenetrable face of a clay brick.

This combined with better insulation in homes, leads to the perfect environment for algae to grow and flourish. Once established, the alage quickly colonise the surface of the wall, leaving unsightly red and black staining.

What is the best method for removing algae on rendered walls?

The new render coatings are enriched with colour pigment, this takes a way the need to paint the walls. The renders are often soft in texture and would be damaged by power washing in an attempt to remove the algae staining.

The safest way to remove algae from outside walls is by the process of soft washing. This method uses specialist chemical cleaners applied at very low pressure ensuring that the integrity of the walls surface is not damaged.

Removing algae from concrete walls or red algae from pebble dash is just a matter of applying the chemical and letting the cleaning action take place.

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So what is the process for removing algae on rendered walls?

The first step in the cleaning process is to identify the type and severity of the biological contaminant present on the render. Moss, algae and lichens can all be treated effectively by softwashing.

The second step is to asses which application method of cleaning is best suited to the type of substrate (rough/smooth) and the level of contaminant

Now that the render has been fully assessed, the cleaning area is made safe to prevent accidental access by the public and all items such as bins, pots, chairs etc are removed from the walls to a safe area.

The most common way we apply the cleaning solution is by a specialised pole and brush system. This is fed by a quiet 12v electric van mounted pump and supply tank, the solution is always applied at low pressure.

Working from the bottom of the wall to the very top, the chemical is applied in a pattern that maximises the coverage and penetration in to the render substrate.

The chemical application is repeated until the walls are free from red algae, moss and lichens. Between each coat we usually allow 30 mins for the chemical to take full effect.

Once the render walls are free from red staining and clean, they are rinsed down with a heavy but low pressure flow of water. This removes any remaining chemical and biological debris. This ensures an even, clean finish.

As professional cleaners we do our best to keep splashing of the chemical treatment to a minimum. It is inevitable that with soft washing the reveals and other areas, render cleaning chemical will find its way on to other surfaces, so in this stage we wash down all paving, window sills, lead flashing and your windows are treated to a pure water clean.

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