Facade cleaning methods: which one suits your building?
Team OPPY4 min read
Facade cleaning can be done with high pressure, softwash at low pressure, chemical products, enzymatic products, steam or hot water, gentle abrasive methods and poultices. The right method depends on the facade material, the type of soiling and the condition of joints and render. High pressure suits hard, dense materials, and a test patch settles it.
Anyone having a facade cleaned is soon offered a choice of methods: pressure washing, softwash, a chemical product, enzymes or steam. Each has its place, but not on every facade. Below you will find which facade cleaning methods exist, which one suits which facade material and how to choose.
Which facade cleaning methods are there?
Broadly three families: cleaning with water, with a product and by mechanical means. Below we mainly follow the Dutch Cultural Heritage Agency (RCE) and the US National Park Service (NPS).
Pressure washing
With pressure washing, the force of the water jet loosens the dirt. According to the RCE, high pressure is mainly intended for hard, dense materials such as granite and brick masonry, and should be applied with care because the surface can easily be damaged (RCE). The NPS warns that water at too high a pressure can etch marble, other soft stones and some types of brick. Grains of stone or sand in the run-off suggest the pressure is too high (NPS).
Softwash at low pressure
With softwash, a product does the work: it is given time to act, and the facade is then rinsed at low pressure. The NPS describes the same sequence for chemical cleaners: wet the masonry, apply the cleaner at very low pressure, let it dwell and rinse it off (NPS). There is more in what is softwash and facade cleaning without high pressure.
Chemical products: acidic, alkaline and biocides
According to the NPS, acidic cleaners suit materials that are not acid sensitive, such as granite, most sandstones, unglazed brick and concrete. Alkaline cleaners are meant for acid-sensitive materials such as limestone, marble and glazed brick. Both can leave salts or stains if they are not rinsed off properly (NPS). Why household bleach is a poor choice is covered in bleach on facades.
The RCE notes that biocides are mainly used to kill fungi, algae, mosses and lichens. Such a product falls under the EU Biocidal Products Regulation (EU) 528/2012: it may only be placed on the market or used if its active substances are approved and the product itself has been authorised (European Commission).
Enzymatic products
According to the RCE, enzymes are proteins that can break down the attachment of biological soiling. They therefore target organic dirt. How that works and when you see results is explained in enzymatic facade cleaning.
Steam or hot water
The RCE describes cleaning with saturated steam at 100 to 150 °C as relatively safe, because the facade surface and any patina are usually left intact (RCE).
Gentle abrasive methods
Blasting works by abrasion. The NPS considers abrasive methods generally unsuitable for historic masonry and accepts gentle, controlled abrasive cleaning only on limited, hard-to-clean areas under the supervision of a conservator, never on an entire building (NPS).
Poultices
A poultice is a paste of an absorbent material, such as kaolin, mixed with a liquid. As it dries, it draws stains and graffiti out of the stone (NPS).
Which method suits which facade material?
Hard, dense materials tolerate more than soft or coated surfaces. The table gives a first direction; the manufacturer's instructions and a test patch decide.
Facade cleaning by facade material
| Suitable approach | What to watch out for | |
|---|---|---|
| Brick | High pressure on hard brick masonry, otherwise a product at low pressure; an acidic cleaner can suit unglazed brick | Joints must be sound; abrasive blasting removes the fired skin of the brick |
| Natural stone | Granite tolerates high pressure; limestone and marble need low pressure, steam or an alkaline cleaner | Acids attack limestone and marble; seek advice first on heritage buildings |
| Render | Softwash: a product suited to the render, rinsed at low pressure | Thin top layer; have cracks and loose areas checked first |
| Concrete | Pressurised water or steam, depending on how dense the concrete is; an acidic cleaner can suit | Test patch for colour and texture |
| HPL and Trespa | Water with a general household cleaner, soft sponge or nylon brush, then rinse | No abrasive or polishing agents; follow the manufacturer's instructions |
| Coated steel and sandwich panels | Regular rinsing with clean water, with a product intended for coated metal | Sheltered areas the rain does not wash, such as under eaves |
| Aluminium | A mild product, following the coating or system supplier's instructions | Do not damage the coating or anodised layer; test patch |
| Glass | Pure water or a mild, non-abrasive glass cleaning solution | No acids on glass; account for rinse water running down from the facade |
According to Trespa's cleaning documentation, the surface of its HPL panels is closed and virtually pore-free, cleaning agents with abrasive or polishing components should not be used, and recommended concentrations and soaking times should not be exceeded (Trespa). Steel producer BlueScope recommends regular washing of its pre-painted steel with clean water, especially the areas the rain does not reach (BlueScope). For glass, the US National Glass Association states that cleaning solutions should not contain acids (NGA). Why window cleaners work with pure water is explained in what is osmosis water.
How do you choose a method for building facade cleaning?
First establish what needs to come off and from which surface, then have test patches made, starting with the gentlest method. These points carry the most weight.
The type of soiling. The NPS starts every cleaning project by identifying what is to be removed (NPS). Organic soiling such as algae and moss needs a different product from mineral soiling such as lime and cement residue. The causes of green growth and how to deal with it are covered in green growth on facades.
The test patch. The RCE advises having test patches made before a method is chosen, on both heavily and lightly soiled areas.
The condition of joints and render. Before any water cleaning, all mortar joints should be sound and the building watertight; otherwise water can seep through to the interior (NPS).
Heritage status. Cleaning can cause physical and visual damage, and in the Netherlands a protected monument requires an environmental permit (RCE). For a listed or protected building elsewhere, check which consent is needed before you start.
The weather. Do not clean with water when frost is expected. Water that freezes in the masonry can cause spalling and cracking, and a wall may take over a week to dry after cleaning (NPS).
In Belgium, Buildwise Technical Information Note 296 (2025) covers the types of soiling, the methods and the precautions for facade cleaning (Buildwise).
How we do it at OPPY
We assess every facade first and choose per material between softwash at low pressure and high pressure up to 200 bar: softwash where the facade is sensitive, high pressure where the surface can take it and the dirt calls for it. We work with purified water and with enzymatic and chemical products, depending on the dirt and the surface. The enzymatic products break down organic dirt and keep working after a single application. For sandwich panels and metal cladding we use specialised products. We only claim an effect against algae or moss for a product authorised for that purpose.
If we spot failing joints, cracked render or loose elements, we tell you before we start. We clean with technology we control from the ground, such as drones and robotics, and rinse the windows in the facade with purified water. In rain or strong wind we don't fly. Thick crusts or graffiti sometimes need another technique, and when that is the case, we'll tell you.
To see how a cleaning job runs, go to Facade cleaning.
Sources
- Gevelreiniging, Rijksdienst voor het Cultureel Erfgoed (RCE, Dutch Cultural Heritage Agency), Kennisbank
- Preservation Brief 1: Assessing Cleaning and Water-Repellent Treatments for Historic Masonry Buildings, U.S. National Park Service, Technical Preservation Services
- Gevelreiniging (Technische Voorlichting 296), Buildwise
- Regulation on the supply and use of biocidal products, European Commission
- Cleaning and maintaining Trespa Meteon (technical documentation EN-US3064, version 3.1), Trespa (document hosted by distributor CEI Materials)
- Easy to Maintain, BlueScope (COLORBOND steel)
- Glass Technical Paper FB01-00 (2023): Proper Procedures for Cleaning Architectural Glass Products, National Glass Association (NGA)
Frequently asked questions
Which facade cleaning method is best?
No method is best on every facade. The facade material, the type of soiling and the condition of joints and render decide. Heritage bodies advise making test patches and starting with the gentlest method that removes the dirt.
Is pressure washing bad for a facade?
Not by definition. The Dutch Cultural Heritage Agency describes high pressure as mainly intended for hard, dense materials such as granite and brick masonry, applied with care. On marble, other soft stone, some brick and weak joints, water at too high a pressure can damage the surface.
What is the difference between chemical and enzymatic facade cleaning?
A chemical cleaner, acidic or alkaline, dissolves or loosens the dirt and is then rinsed off. Enzymes are proteins that can break down the attachment of biological soiling, so they target organic dirt such as algae and moss. Lime or cement residue needs a different product.
Do you need a permit to clean a facade?
For an ordinary facade, usually not. For a protected monument in the Netherlands, the Dutch Cultural Heritage Agency says an environmental permit is required, because cleaning can cause damage. For a listed or protected building elsewhere, check with the local heritage authority first.
About the author
Team OPPY
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