Professional methods for cleaning plaster facades

Rendering exterior walls is a common architectural practice that offers versatile texture and colour options for building facades. To ensure that the shell of a building retains its aesthetic appeal, regular cleaning must be carried out in addition to repainting when needed. Our tips below will help you with plaster facade cleaning.

Why rendered walls? Advantages and disadvantages

Exterior walls should be able to withstand the elements for many years, retaining their original appearance with minimal maintenance. Ideally, they are easy to care for, breathable and provide good thermal insulation. Rendering is a construction technique that has been around for centuries, and you can find renders that have mineral or acrylic binders.

Mineral renders have a porous structure, enabling them to absorb and release moisture, preventing it from becoming trapped inside a building‘s facade. The high pH value of mineral renders also makes them resistant to mould, fungus and moss. While mineral renders are robust and inexpensive, it takes a long time for them to dry. To maintain mineral render and ensure its protective function lasts, it’s important to clean plaster facades regularly and apply a new coat of paint when necessary. Silicate and emulsion paints are durable options that are suitable for walls with mineral rendering and can be applied several times if needed.

In acrylic renders, synthetic resin is used as the binder, which gives facades an elastic quality. This type of render can withstand different temperatures and humid weather conditions, resulting in fewer cracks. Faster drying times and the synthetic resin’s ability to bind to substrates make the application of acrylic renders easier. However, the material’s reduced breathability makes it susceptible to fungus, moss and algae infestations. Like their mineral counterparts, acrylic plaster facades must also be regularly cleaned and repainted from time to time. After a longer period of time, the render should be renewed.

What to pay attention to when cleaning plaster facades with high-pressure

High-pressure cleaners have established themselves as a standard in plaster facade cleaning and are an ideal choice. Pressure washing produces exceptional results even when tasked with removing dust and soot that has settled into the porous, rough surfaces that are characteristic of rendered walls.

Cleaning plaster facades: a matter of selecting the correct pressure, detergent and temperature

To get the best results when cleaning a plaster facade, you’ll want to first assess the type and intensity of the soiling. This will help you to identify the appropriate approach to cleaning the surface in question. Prior to starting your clean, you’ll need to decide on the optimal combination of pressure, cleaning agent and/or temperature. By testing this out beforehand, you can avoid damaging a building’s exterior. To not damage the paint or cause surface abrasion, it’s important to not spend too long cleaning one area of a wall. Additionally, working from the top of a wall downward will help to prevent runners (traces of dirty water on surfaces that have already been cleaned).

Loose dust particles can easily be removed by pressure washing with cold water. For a more intensive clean, you can use a cleaning detergent or gel cleaner. Gel cleaners are an effective option due to their ability to bind to the surface of walls. Make sure that the detergent you use is an alkaline cleaner and only use the amount specified in the manufacturer's instructions. Once the application time has elapsed, rinse the facade with water.

A person cleaning a plaster facade with a Kärcher High-Pressure Cleaner.

A man cleaning a plaster facade with a Kärcher high-pressure cleaner.

If the soiling is oily or greasy – for example, as a result of using oil or coal heating systems – using a pressure cleaner with hot water is a good option to remove such staining. Temperatures between 60 °C and 80 °C are able to dissolve encrusted dirt and other deposits quickly and thoroughly. For particularly stubborn stains, you can employ the steam setting on a pressure washer. The steam that is released can reach temperatures of up to 155 °C. At a distance of 10 cm, the steam will be measure between 60 °C and 80 °C by the time it reaches the surface of the building you are cleaning. The steam is able to penetrate the porous structure of the render, destroying algae and moss at its source and ensuring an intensive clean. In contrast to pressure washing with cold water, pressure washing with higher temperatures shortens the time needed for drying, making it possible to carry out any follow-up work directly after you are done cleaning.

Tip – Tap on insulating render before cleaning it:

Time leaves its mark in the form of crumbling render and peeling paint. By tapping on the wall, you can detect loose or drummy render. Should you detect damage, it’s best to hold off on cleaning the plaster facade. If you’re already in the process of cleaning the wall, stop immediately to prevent damage from occurring. You’ll either need to apply a new coat of render or, in some cases, it may be necessary to carry out more in-depth renovations.

Cleaning with a Kärcher hot water high-pressure cleaner

Advantages of hot water high-pressure cleaners

Cleaning with hot water: High-pressure cleaners clean even better at a constant pressure. Alongside improved results and faster cleaning and drying times, hot water high-pressure cleaners also have a measurable germ-reducing effect. When the steam stage is used, even delicate surfaces can be gently cleaned with temperatures of up to 155 °C. Furthermore, the machines allow for a reduction in the working pressure, the time required and the volume of cleaning agent that is used. This means that cleaning with hot water offers a number of advantages and various possibilities for optimising the cleaning process.

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Tips for cleaning plaster facades efficiently and gently

To protect the surface of the walls you are cleaning, you can attach a flat-jet nozzle to your pressure washer. Working at a distance of 20 to 50 cm will allow you to distribute the water pressure better. It’s also important that the pressures cleaner you are using has different settings. By being able to adjust both pressure and flow control, you can prevent too much pressure or water from reaching the surface you are cleaning. If cleaning agents were used during your clean, you’ll need to collect and dispose of any loose render according to local regulations.

Using the right technology and equipment for your clean will ensure you don’t incur unnecessary costs. Scaffolding, while necessary for tall buildings, doesn’t need to be used for residential housing with fewer storeys. There are many high-pressure cleaning systems available on the market that incorporate water-fed poles, providing you with a more affordable, ergonomic alternative for cleaning areas high up. Additionally, such systems also offer different brush options with varying degrees of stiffness. If you are cleaning thermal insulated facade systems, soft bristles are ideal.