What is soft washing a building, and is it suitable for commercial buildings?
Team OPPY4 min read
Soft washing a building means applying a product suited to the surface to loosen the dirt, then rinsing the facade at low pressure. For offices, hotels and industrial halls with brick, render, HPL or coated steel panels it is often a good fit, provided the product and method are chosen for each surface.
Compare a few quotes for facade cleaning and sooner or later you will meet the word softwash, or soft washing. This article explains what soft washing is, which products it uses, which commercial facades it suits and where its limits lie.
What is soft washing a building, exactly?
Soft washing is a method in which a cleaning product loosens the dirt and a low-pressure rinse then carries it away. A pressure washer works the other way round: it removes dirt by the force of the jet.
First the product goes on the facade and is given time to work. Then the facade is rinsed from top to bottom at low pressure. The chemical supplier Alliance Chemical describes soft washing as a method in which the chemistry does the heavy lifting, with a dwell time before the rinse and a pressure far below that of a pressure washer (Alliance Chemical).
The difference from pressure washing lies mainly in what happens to the surface. The Cultural Heritage Agency of the Netherlands points out that high-pressure spraying carries risks, especially for softer brick and historic mortar joints (RCE). At low pressure, that mechanical strain is much smaller. The full comparison is in cleaning a facade without high pressure.
Which products are used in soft washing?
That depends on the contractor. Many soft washing companies use a mix based on sodium hypochlorite, while others choose enzymatic or other products.
Sodium hypochlorite is the active ingredient in household bleach. Alliance Chemical calls it the standard for soft washing and combines it with a surfactant, so the mix clings better to vertical surfaces. The same supplier warns that sodium hypochlorite kills plants on contact, advises soaking plants and soil thoroughly beforehand, and advises against using it on bare steel (Alliance Chemical). The pros and cons of chlorine on facades are covered separately in cleaning a facade with bleach.
A product that kills algae or moss is a biocide. In the European Union, a biocidal product cannot be placed on the market or used unless it contains approved active substances and has been authorised (European Commission). So ask every contractor which product will go on your facade, and ask for its safety data sheet.
Which commercial buildings and facades is soft washing suitable for?
For most facade materials on offices, hotels and industrial sites, provided the product and method are chosen for each surface.
Brick, render and mortar joints are sensitive to high pressure, and that is exactly where low pressure helps. HPL (high-pressure laminate) cladding panels have a closed, non-porous surface. The manufacturer Fundermax writes that rain already washes much of the dirt off its HPL panels, that you rinse them with clean water, and that abrasive scouring pads and powders should not be used (Fundermax). The coated steel panels of warehouses and production halls need a product that does not attack the paint finish. Steelmaker BlueScope recommends washing pre-painted steel regularly with clean water, especially the parts that rain does not reach, such as wall cladding under eaves (BlueScope).
Soft washing on the facade materials of commercial buildings
| Where you find it | Point of attention | Soft washing | |
|---|---|---|---|
| Brick and mortar joints | Offices, hotels | Joints cope poorly with high pressure and acids | Suitable, with a product that does not attack brick or joints |
| Render and decorative plaster | Offices, hotels | Soft layer, green growth mostly on the north side | Suitable, low pressure is the very advantage here |
| HPL cladding panels | Offices, commercial buildings | No abrasives, follow the manufacturer's instructions | Suitable, within the manufacturer's instructions |
| Coated steel panels | Warehouses, production halls | Product must not attack the paint, seams need attention | Suitable, with a product made for coated metal |
| Historic natural stone | Protected buildings | Risk of physical and visual damage | Specialist heritage advice first |
What are the limits of soft washing?
Soft washing works best on organic dirt such as green growth, algae and a grey film of grime. Mineral deposits, graffiti and historic facades often need a different approach.
Limescale, cement residue and rust are mineral deposits. A product meant for organic growth does not dissolve them, and a targeted treatment by a specialist is then the better route. Thick crusts and graffiti sometimes need another technique.
On heritage buildings, caution is the rule. The RCE writes that cleaning can cause both physical and visual damage, that the lighter the cleaning, the smaller the risk of damage, and that test panels should be made first, on both heavily and lightly soiled areas. For a protected monument, a permit is often required (RCE). The US General Services Administration takes the same line: the gentlest method first, small test patches, and no raw acids or alkalis on masonry (GSA).
The weather matters too: the GSA does not allow cleaning when rain, snow or freezing temperatures are expected within the next 24 hours. Then there is the rinse water. It runs down the facade, over windows and frames, towards planting and drains. The GSA asks for glass, woodwork and metal to be protected from overspray, and for planting to be protected from run-off (GSA).
How is soft washing done at height?
The principle stays the same; only the way of reaching the facade changes: from an aerial work platform, by rope access, from a gondola or with a drone.
An aerial work platform needs firm ground and takes up a car park or entrance, rope access needs anchor points on the roof, and a gondola hangs from a permanent rooftop installation (BMU, building maintenance unit). With a drone, the pilot stays on the ground. Because soft washing works at low pressure, a drone can both apply the product and rinse. In rain or strong wind, a drone does not fly.
How we do it at OPPY
Softwash is one of our methods, alongside pressure washing up to 200 bar. With softwash, a product suited to the surface loosens the dirt, and we then rinse with purified water at low pressure. We choose the product and its dilution for each surface. We use enzymatic and chemical products; the enzymatic ones stay active for a while after a single spray. 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, and you can ask for the safety data sheet of every product we use.
We clean with technology we control from the ground, such as drones and robotics, and choose the most efficient approach for each building. If we spot failing joints or cracked render, we tell you before we start. Where the rinse water ends up and how we drain it away is assessed for each building, and we 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.
For the method and what sets the price, see Facade cleaning.
Sources
- Pressure Washing Chemicals Guide: Types, Uses & Selection Tips, Alliance Chemical
- Regulation on the supply and use of biocidal products, European Commission, DG Health and Food Safety
- Gevelreiniging (facade cleaning), Cultural Heritage Agency of the Netherlands (RCE)
- Cleaning historic masonry: Removal of atmospheric soiling, stains, and biological growth, U.S. General Services Administration (GSA)
- How to Clean High-Pressure Laminate Panels, Fundermax
- Easy to Maintain, BlueScope (COLORBOND steel)
Frequently asked questions
Is soft washing the same as cleaning a facade with bleach?
Not necessarily. Soft washing describes the method: let a product work, then rinse at low pressure. Many contractors use a mix based on sodium hypochlorite, the active ingredient in household bleach, while others use enzymatic or other products. Always ask which product will go on your facade and ask for its safety data sheet.
Does soft washing remove limescale or cement residue?
Usually not. Limescale, cement residue and rust are mineral deposits, and a product meant for organic growth does not dissolve them. They need a targeted treatment, often by a specialist and with a product matched to the surface.
How long does a facade stay clean after soft washing?
That depends on the exposure, the material and the product, so there is no fixed figure. A north-facing facade under trees turns green faster than a south-facing one in open ground, and a facade along a busy road turns grey faster.
Can soft washing be done with a drone?
Yes. Because soft washing works at low pressure, a drone can apply the product and rinse the facade, flown by a pilot on the ground. In rain or strong wind the drone does not fly and the job is rescheduled.
About the author
Team OPPY
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