Why does my render looks sad?

If you are asking yourself that same question, you are not alone!

Many people buy Rendered homes, they look great once built, only find out a few years later when Algae starts to grow on the render  making the building look unsightly

If you’re thinking about re-painting, Let me stop you there, Painting render is one of the worst things you can do to a rendered building, K-Rend and other renders are porous and are designed to breath, so potentially your trapping the moisture in!

by painting you will have potentially stopped the house being able to breath trapping the algae under the paint which will ultimately over time keep growing. It’s got to grow somewhere right?

That’s right, its going to blow the paint work and potentially the render, causing extensive damage.

Let’s firstly look at how the render has got in that state in the first place.

There was an in depth study done in Sweden which you can read on more

Linked here: (http://portal.research.lu.se/portal/files/4086826/1963564.pdf)Citation for published version (APA): Johansson, S. (2011). Biological growth on rendered façades Lund University, Division of Building Materials

Here is the general rule of thumb on why you have Microorganisms growing on your render.

For hundreds if not thousands of years mould, algae and spores have been growing in many different areas way before you and I were born! as the world is teeming with different organisms on stones and vertical cliffs, Modern buildings and houses have given new opportunities for some organisms to expand by using buildings as habitats.

Contamination on Render is not only of aesthetical character as these microorganisms are actually eating and decomposing your surfaces at an alarming rate. Biological growth on buildings is highly unwanted and can be harmful or degrade the building itself.

Moisture is the single most important factor for biological growth on render

There are 4 main culprits which are growing on your render


Algae, sometimes called terrestrial algae, can live in terrestrial environments as, for instance, on tree trunks or on rendered buildings


When the right moisture conditions are available, the render can achieve a black-coloured mould Cladosporium which is a common saprotroph organism, therefore also often found in the air.

Another common air-borne mould that can be found on rendered buildings is  Alternaria is a genus of ascomycete fungi. Both these moulds are black because of the pigment melanin that protects them against strong UV-radiation


Lichens are composite organisms, a symbiotic association of fungi (the mycobiont) and algae or cyanobacteria (the photobiont) that are lich. Organisms on façades enized in a unique morphology. Lichens are by now described by the mycobiont and are therefore a part of the fungal kingdom,  but were in long time thought of as plants, just as fungi were.


Mosses belong to the kingdom of plants which have many characteristics in common with green algae. Mosses are placed in a division of spore-bearing plants (Bryophyta). Mosses are photoautotrophic organisms, using light as energy source by photosynthesis

how do you stop this growing on your rendered house?

Slight problem you can’t it’s one of those things you have to manage and maintain, moisture is always going to be around in this country, we have the good old English weather to thank for that!

However you can kill what is already there by getting it cleaned and treated on a regular basis or every few years. It will be more cost effective than getting the render painted, also will maintain the look of your building for a longer period of time without causing damage to your render.

Using bleach based solution killing the Microorganisms at route bacteria, moulds, fungi, protozoa and algae, among others. Bleach kills illness-causing microorganisms by attacking the proteins that make up the bacteria, algae, etc. This causes the proteins to unfold and break apart which leads to the death of the microorganism.

Leaving your render looking great again, sanitising and cleaning the area with proven success.

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