Effective facades cleaning – from plaster to metal

If the exterior of a building is maintained this helps retain or increase its value. Various methods are available to clear dirt from facades. But the surface should be taken into consideration when applying the respective technology. This is essential for avoiding damage. An overview about techniques and regulations.

facades cleaning

The standard: Cleaning with hot water and steam

Facades are the flagships of buildings. Often they are large, complicated surfaces made of different materials. Exposed to external environmental influences for years, dirt can settle and accelerate weathering in different ways.

Hot water high-pressure cleaners have proven an effective, economical method in facade cleaning due to their high cleaning performance by low water consumption. With trailer based variants even self-sufficient working, independently of electricity and water network, is possible.

The advantages of hot water high-pressure cleaners compared to cold water high-pressure cleaners are based on two aspects:

Unlike the cold water high-pressure cleaner, the user can, besides water volume and pressure, also use the temperature factor with hot water machines. If cleaning is done in a temperature range between 60 and 80 °C, this leads to a significantly faster breakup of encrusted dirt and deposits. Oil, grease and soot can be removed more easily. The depth penetration is also higher so that roots of moss and lichens are removed, thus preventing any regrowth.

Hot water high-pressure cleaner

A final tip when using hot water high-pressure cleaners is the steam stage: The water volume is reduced by half, and up to 155 °C steam is discharged. Very intensive cleaning is possible, which effectively tackles even stubborn dirt such as paints or bituminous coatings. The low working pressure protects sensitive surfaces.

Steam stage
Information

A preliminary test is wise:

Choose the right technology, avoid damage.

No matter which facade material is present – in order to select the correct technology, in each case a sample area should be tested extensively beforehand. Is the facade sensitive to acids, does it absorb water? Which cleaning agent achieves the desired effect in which concentration and time? Those who proceed carefully in advance achieve the desired result and avoid loss of substance or substance removal or other permanent damage due to the incorrect cleaning agent.

It's all about the material: Cleaning of different facade types

natural and artificial stone facades

plaster facades

wooden facades

metal facades

    Enhanced effect due to cleaning agents

    A cleaning agent can further enhance the effect of a high-pressure cleaner if required. The so-called two-step method is recommended in the application. Here the cleaning agent is applied first, it is then washed off at high pressure after the application time. However, when selecting the cleaning agent both the quality of the surface and the statutory provisions should be observed.

    Natural and artificial stone exists in acid-sensitive variants (marble, dolomite, travertine, jura, Solnhofen slabs, calcareous natural stones, as well as cementitious artificial stones) and acid-resistant variants (granite, slate, bricks, tiles, clinker). Pressurised hot water or steam can generally also be used on artificial and natural stone. However, the cleaning agent must be alkaline or neutral for surfaces that are sensitive to acids. Before starting the work it should be noted whether the material is porous, i.e. absorbent – if this is the case it should be watered down before the cleaning agent is applied as otherwise it penetrates the material and may cause damage.

    If the surface is very sensitive to water or the contamination is particularly severe, e.g. graffiti, dry ice is very effective in achieving the desired cleaning result in a fast and gentle manner.

    Pressurised hot water, often in combination with the steam stage, is recommended for plaster façades. The method is gentle and achieves excellent cleaning power. However, too much time should not be spent working on one spot in order to avoid dissolving the paint. A flat jet nozzle has proved to be successful with the use of high pressure for protecting the surface as the selective pressure does not become too high at the correct working distance.

    In each case the user should clean from top to bottom so that so-called runs do not arise – i.e. drops of wastewater that end up in the area that has already been cleaned. The very short drying times of both methods mean that subsequent works can be carried out directly afterwards. A neutral cleaning agent can be used if required to remove soot and oils. It is possible to use a slightly alkaline cleaning agent for finishing coats.

    Wood is probably one of the longest used facade materials and is still very popular today. Untreated wood quickly shows weathering effects; treated wood is protected against weathering with additives such as nano particles. This coating must be renewed regularly in order to retain the uniform appearance.

    Anyone who wants to restore a homogeneous look to untreated wooden façades can achieve excellent results with a hot water high-pressure cleaner. However, care must be taken to ensure that the facade is completely sealed or components that lie behind are not damaged by the water. A frost-free period should also be chosen for the work so that the wood can dry sufficiently after the cleaning. In the case of robust hardwood facades a pressure of 100 bar and a temperature between 60 °C and 80 °C have proven effective, for more sensitive timbers such as larch or spruce a pressure of 50 bar is recommended.

    In order to improve the cleaning result a neutral cleaner can be used for wood.

    Metal facades also require regular cleaning. Aluminium stands out with the formation of a natural oxide layer which protects against corrosion. For anodised aluminium this oxide layer is created artificially whereby the material is particularly hard-wearing. However, the surface is vulnerable to chemicals, from both acids and lyes. In order to prevent damage, neutral cleaning agents are recommended. In advance a sample area should be created and reference measurement be realised before and after the cleaning.

    In the case of coated or painted metal facades it is necessary to remove the so-called chalking (white stains due to washed out pigments). In order to tackle this unpleasant appearance, cleaning agents with grinding additives, as well as suitable facade pads, can be used. The work is carried out manually or with the support of electric, hand-operated polishing machines. Anyone who wants to use high-pressure technology for cleaning should use natural hair or polyamide brushes (fixed or rotating). Only low-pressure water flows out through the large opening at the brush. Thus there is no risk that the high-pressure water penetrates the insulating layer behind the facade.

    Rechtliche Bestimmungen

    Know what's right:

    Requirements and regulations.

    Facade cleaning always takes place in the public arena meaning it is important to obtain information about the requirements and regulations which vary from place to place and from country to country. Wastewater discharge is subject to approval in each case. If it is only dirty water, the water can be discharged after filtration. The solid materials collected must be disposed of. If a cleaning agent was used, the water must be collected, filtered and neutralised. Also with regard to the use of spray agents, the occurrence of dust, noise or exhaust gas, the corresponding regulations must be observed.

    For special cases: Particles and dry ice

    Particle and dry ice blasting are welcome alternatives to high-pressure cleaning. Especially if facades are not to be watered too much or water-saving methods are required. They are also good alternatives to high-pressure cleaners if no cleaning agents should be used or there's a limit for wastewater volume. Both proceedings, particle and dry ice blasting, are also appropriate for removing severe contamination, for example graffiti.

    Particle blasting

    With low-pressure particle blasting a jet gun is supplied with compressed air via an industrial compressor. In addition, a very fine, soft spray agent and water are added to the air in the mixing chamber for dust-binding work. An important factor in the selection of the spray agent is that its Moh hardness and the grain size must be individually selected for the contamination and the original façade surface. The mixture of air, water and spray agent emerges at the nozzle of the trigger gun, whereby air pressure, water volume and spray agent volume are individually adjustable. Surfaces with minimal abrasion can be cleaned in this manner.

    Partikelstrahlverfahren
    Facades cleaning with Kärcher dry ice blasting system

    Dry ice blasting

    For dry ice blasting a blaster, which injects the ice pellets into an air blast unit, as well as a spray hose with trigger gun and nozzle, via which the air-ice mixture reaches the surface, are required. A compressor with sufficient air pressure and airflow rate is also needed. The mechanical energy is decisive for the cleaning performance.

    The dry ice pellets, which have a low Moh hardness (1-2), can be shot onto the surface at a high speed of 150 m/s. This is supported by thermal energy – especially for warm surfaces such as injection moulds – when the frozen CO2 strikes at a temperature of -79° C. As a result, the dirt becomes crumbly and brittle so that it can be easily removed.

    With the barely abrasive method oil, grease, adhesives or binding agents can be removed from various surfaces, sensitive surfaces can be cleaned or paints can also be removed from metal without causing any damage.

    Hot water high-pressure cleaner
    Ice blaster

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