What Is Soft Washing?
Understanding Sodium Hypochlorite and Biocide DDAC in Exterior Cleaning
When it comes to cleaning exterior surfaces—especially roofs, render, patios, and cladding—high-pressure washing isn’t always the best or safest choice. For more delicate materials or stubborn biological growth like algae, moss, and lichen, soft washing is the industry-standard solution.
At Aqua Pro Exteriors, we often get asked about the chemicals we use for soft washing. The two main options are Sodium Hypochlorite and Biocide DDAC (Didecyldimethylammonium Chloride). In this article, we’ll explain what they are, how they work, and when each should be used.
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What Is Soft Washing?
Soft washing is a low-pressure cleaning method that uses specially formulated chemical solutions to treat and remove organic growth on exterior surfaces. Unlike pressure washing, which uses force to blast away dirt, soft washing targets the root cause of staining—killing algae, moss, and lichen at their source.
This makes it particularly suitable for:
• Roof tiles and slates
• Rendered walls
• Painted surfaces and uPVC
• Timber decking
• Patios, stonework, and garden features
Choosing the right chemical solution is critical to achieving safe and lasting results.
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Sodium Hypochlorite – Fast and Effective Surface Cleaning
Sodium Hypochlorite (often referred to as “Hypo”) is a strong oxidising agent widely used in the exterior cleaning industry. It’s the active ingredient in bleach but is used in stronger concentrations in professional soft washing, typically diluted down to 3%–6% depending on the surface and conditions.
How it works:
• Quickly kills moss, algae, mould, and lichen
• Breaks down organic staining on render, stone, brick, and concrete
• Produces visible cleaning results within minutes or hours
Advantages:
• Immediate impact with dramatic visual results
• Cost-effective and efficient for large surface areas
• Ideal for surfaces with heavy soiling or biological build-up
Considerations:
• Requires skilled handling to prevent damage or discolouration
• Run-off can harm plants if not properly controlled
• Surfaces must often be rinsed or neutralised afterwards
At Aqua Pro Exteriors, we use Sodium Hypochlorite only where appropriate and with full attention to surrounding areas, ensuring we protect your garden and property while delivering powerful cleaning results.
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Biocide DDAC – Long-Term Protection Against Regrowth
DDAC (Didecyldimethylammonium Chloride) is a quaternary ammonium compound used in exterior cleaning as a long-lasting biocide. It works differently from Sodium Hypochlorite—rather than providing instant cleaning, it gradually kills and inhibits the growth of biological matter over time.
How it works:
• Destroys algae, mould, and moss at a microbial level
• Prevents regrowth for extended periods (up to 12 months or more)
• Slowly restores surfaces without damaging finishes or pointing
Advantages:
• Offers long-term protection against staining and regrowth
• Safer for sensitive surfaces such as coloured render, cladding, or painted walls
• Generally safe for plants and surrounding environments when used properly
Considerations:
• Does not offer instant visual results (takes several days to weeks)
• Often used after a clean rather than as a primary cleaner
• Higher material cost per treatment compared to Sodium Hypochlorite
DDAC is commonly applied by Aqua Pro Exteriors as a final treatment after cleaning to prevent regrowth and extend the cleanliness of the surface.
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Choosing the Right Treatment
Both Sodium Hypochlorite and DDAC biocide have their place in soft washing. The decision depends on the surface, level of soiling, desired outcome, and environmental considerations. Below is a quick comparison.
Sodium Hypochlorite DDAC Biocide
Fast visual cleaning Yes No
Deep organic removal Yes Yes
Long-term prevention No Yes
Surface safety Requires care Generally safe
Environmental impact Requires run-off management Low if used responsibly
Ideal usage Heavy stains, render, patios Roofs, render, after-clean treatments
At Aqua Pro Exteriors, we assess each property individually and select the appropriate solution—or a combination of both—to ensure the best possible results.
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Health, Safety, and Environmental Responsibility
All chemicals used in soft washing are handled in accordance with UK regulations and COSHH guidelines. We are fully trained, insured, and take every precaution to protect your home, family, pets, and garden. This includes:
• Using the correct PPE and dilution rates
• Pre-soaking or shielding plants and delicate areas
• Containing and neutralising run-off where required
• Never overapplying or leaving chemicals to dry on surfaces
Your safety and the long-term condition of your property are our top priorities.
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Book a Professional Soft Washing Service
If you have render that’s stained green, patios that look tired, or a roof showing signs of moss and lichen, Aqua Pro Exteriors can help. With the right chemical treatments, we can clean safely, effectively, and leave surfaces protected for months to come.
For a free consultation or no-obligation quote, get in touch today.
Call: 07830384856
Or please reach out to us via our contact form
