How to Mix Softwash Solutions Correctly
To mix a softwash solution correctly, you must know the strength of your concentrate, decide the safe target strength for the surface, measure accurately, add water first, add chemical carefully, then add any approved surfactant or additive last. The solution should be mixed only in suitable chemical-resistant containers, applied with appropriate equipment, and used in line with the product label, safety data sheet, COSHH assessment and site-specific risk assessment.
For UK exterior cleaning contractors, facilities managers and serious DIY users, correct softwash mixing is not just about achieving a clean result. It affects safety, surface protection, plant care, legal compliance, customer trust and job profitability. Over-mixing wastes chemical and increases risk. Under-mixing can lead to poor results, callbacks and unnecessary repeat applications.
This guide explains how to mix softwash solutions in a practical, professional way, including dilution calculations, common target strengths, equipment considerations, and the mistakes we regularly see on patios, render, roofs, cladding and commercial sites.
What Is a Softwash Solution?
A softwash solution is a controlled cleaning mixture used to treat organic contamination such as algae, lichen, moss, mould, mildew and biofilm on exterior surfaces. Unlike pressure washing, softwashing relies on chemistry and controlled dwell time rather than high-pressure force.
Most professional softwash systems in the UK use one of the following approaches:
- Sodium hypochlorite-based cleaning: commonly used for rapid removal of organic staining on suitable hard surfaces.
- Biocidal treatment: often used for longer-term control of organic growth, particularly where a slower acting treatment is more appropriate.
- Specialist stain removers: used for rust, oil, tannin, lead staining or other stains that are not organic growth.
- Surfactant-enhanced softwashing: where an approved surfactant helps the solution cling, penetrate and wet the surface more evenly.
SoftWash UK supplies professional soft wash chemicals for these different cleaning tasks, but the important point is that each product must be used for the correct purpose and mixed only as directed.
The Golden Rule: Know Your Starting Strength and Your Target Strength
The most common mixing mistake is guessing. A contractor may say they are using “a 4% mix”, but that could mean several different things depending on whether they are talking about container concentration, tank mix, injector output or surface-applied strength.
For accurate softwash mixing, you need to understand two figures:
- Stock strength: the strength of the concentrate you are starting with, such as sodium hypochlorite at 14% to 15% available chlorine.
- Target strength: the final strength you want in your mixed solution or at the point of application.
If you are using sodium hypochlorite for soft washing 14% to 15%, the mix calculation must be based on the actual product strength and the final volume you want to make. Never assume that all drums are the same strength, and remember that sodium hypochlorite degrades over time, especially when stored warm, in sunlight or for long periods.
The Basic Softwash Dilution Formula
The standard dilution formula is:
Litres of concentrate required = target strength ÷ stock strength × final volume
For example, to make 20 litres of a 3% sodium hypochlorite solution using 15% sodium hypochlorite:
- 3 ÷ 15 × 20 = 4 litres of sodium hypochlorite
- 20 litres final volume minus 4 litres chemical = 16 litres of water
So the mix is:
- 16 litres water
- 4 litres 15% sodium hypochlorite
- Approved surfactant if required, added according to the label
Quick Reference Mixing Table for 15% Sodium Hypochlorite
The following table gives simple examples for mixing sodium hypochlorite solutions using 15% stock strength. These are not universal recommendations for every surface. Always carry out a test patch and follow product guidance.
| Final Volume | Target Strength | 15% Sodium Hypochlorite Required | Water Required | Typical Use Case |
|---|---|---|---|---|
| 10 litres | 1% | 0.67 litres | 9.33 litres | Light organic staining on suitable surfaces |
| 10 litres | 2% | 1.33 litres | 8.67 litres | Moderate algae and biofilm on compatible masonry |
| 20 litres | 3% | 4 litres | 16 litres | Heavier organic staining on suitable hard surfaces |
| 20 litres | 4% | 5.33 litres | 14.67 litres | Severe staining where the surface is compatible and risk controlled |
| 100 litres | 2% | 13.33 litres | 86.67 litres | Larger commercial batch where accurate measuring is essential |
If your sodium hypochlorite is 14% rather than 15%, the numbers change. That small difference matters on larger jobs. A professional contractor should always calculate from the actual stock strength rather than using a rough rule of thumb.
Step-by-Step: How to Mix a Softwash Solution Safely
1. Survey the Surface First
Before mixing anything, inspect the surface. A roof, K-rend wall, block paved drive, Indian sandstone patio and powder-coated cladding panel do not all need the same chemistry or strength.
Check for:
- Surface material and condition
- Previous sealers, paints or coatings
- Oxidisation, chalking or weak finishes
- Metal fixtures, lead flashing, aluminium trims and painted details
- Nearby plants, lawns, ponds and watercourses
- Drainage routes and run-off control
- Public access and overspray risk
A good mix begins with a good survey. If you do not know what you are treating, you cannot choose the correct chemical strength.
2. Decide the Correct Cleaning Approach
Not every job needs sodium hypochlorite. Some maintenance programmes are better suited to a biocide, particularly where the objective is slower organic growth control rather than immediate whitening. Delicate surfaces may need lower strength, more dwell time and careful agitation instead of a stronger mix.
As a practical rule, use the weakest effective solution for the task. Stronger is not automatically better. Stronger can mean greater risk to plants, metals, coatings, clothing, skin, eyes and surrounding surfaces.
3. Prepare Your Mixing Area
Mix in a controlled area away from members of the public, pets, open drains where pollution risk exists, and vulnerable surfaces. Use a stable, level position and avoid mixing in windy conditions.
You should have:
- Chemical-resistant gloves
- Eye and face protection
- Suitable protective clothing
- Clean water for dilution and emergency rinsing
- Accurate measuring containers
- Clearly labelled chemical-resistant containers
- Access to the relevant safety data sheets
- Spill control materials where appropriate
For professional sites, especially commercial or facilities management work, a written risk assessment and method statement is good practice and often required. SoftWash UK provides a Risk Assessment and Method Statement pack for exterior cleaning, which can help contractors structure safety documentation properly rather than relying on generic paperwork.
4. Add Water First
Always add clean water to the mixing container first, then add the measured chemical concentrate. This reduces splash risk and helps the concentrate disperse more evenly.
Do not pour from height. Do not rush. Do not mix next to open vehicle doors, customer possessions, painted gates or sensitive landscaping. Most softwash incidents we hear about are caused by haste, poor positioning or careless decanting rather than a complicated technical failure.
5. Add the Chemical Concentrate Carefully
Measure the concentrate accurately and add it slowly. If using sodium hypochlorite, avoid contact with skin, eyes, clothing and unsuitable surfaces. Make sure all containers are compatible and clearly labelled.
Never mix sodium hypochlorite with acids, ammonia, vinegar, descalers, toilet cleaners, solvent-based products or unknown residues. Dangerous chlorine gas can be produced if sodium hypochlorite is mixed with incompatible chemicals.
6. Add Surfactant Last, If Required
A surfactant can improve wetting, cling and dwell time, especially on vertical render, cladding, fascias and textured surfaces. It can also help you see where you have applied the solution and reduce run-off when used correctly.
Use only a surfactant suitable for softwashing and follow the manufacturer’s dosage guidance. SoftWash UK’s Clever Wash Surfactant is designed for professional softwashing applications where improved cling and surface contact are useful. Do not add washing-up liquid or random detergents to a chemical mix. Household detergents are not designed for professional exterior chemical application and may create unwanted reactions, excessive foaming or rinsing problems.
7. Mix Gently and Use Promptly
Once the components are added, mix gently using the movement of the container or system circulation if appropriate. Avoid aggressive agitation that creates splashing or excessive foam.
Use mixed sodium hypochlorite solutions promptly. Once diluted, the active strength can reduce over time, particularly in warm weather or sunlight. Do not leave unlabelled mixed chemical in the back of a van for future use.
Choosing the Right Strength for Common UK Surfaces
The correct mix depends on contamination, surface type, weather, access, dwell time and customer expectation. The table below gives general guidance for professional thinking, not a substitute for product instructions or site judgement.
| Surface or Task | Typical Issue | Mixing Consideration | Best-Practice Note |
|---|---|---|---|
| Render and painted masonry | Green algae, red algae, atmospheric staining | Often benefits from lower-strength controlled application with surfactant | Test patch first; check paint condition and manufacturer guidance |
| Concrete and block paving | Algae, black organic staining, general grime | Moderate strength may be used where surface is compatible | Control run-off and protect adjacent lawns and planting |
| Natural stone | Organic growth, lichen, ingrained staining | Requires careful testing; some stones are sensitive or previously sealed | Avoid assuming all sandstone, limestone or slate behaves the same |
| Roof tiles | Moss residue, lichen, algae staining | May require specialist approach, controlled application and run-off management | Work-at-height planning, gutter control and property protection are critical |
| Cladding and commercial elevations | Biofilm, traffic film, weathering | Often suited to lower strength, surfactant and careful rinse procedure | Check coating warranties and avoid application in wind |
| Timber | Algae, greying, surface contamination | Needs specialist assessment; strong oxidisers can affect colour and fibres | Consider timber-specific cleaning and brightening methods |
Batch Mixing Versus Proportioning Systems
There are two main ways contractors apply softwash solutions: batch mixing and proportioning or injection systems. Both can work well, but they require different thinking.
Batch Mixing
Batch mixing means preparing a known volume of solution in a tank or container before application. This gives good control because you know the exact starting strength and final volume.
Batch mixing is useful for:
- Smaller domestic jobs
- Controlled treatment areas
- Jobs where a known, consistent tank strength is required
- Contractors who are still building experience with dilution calculations
The downside is that you may mix too much, leading to waste, or too little, causing interruptions. You also need to manage transport, storage and labelling carefully.
Proportioning and Injection Systems
Proportioning systems mix chemical and water at a controlled ratio during application. They can save time and reduce handling when set up properly. However, the operator must understand output ratios, flow rates and actual on-surface strength.
Equipment such as the Clever Injector Dosatron can be useful for contractors who want more controlled dosing, particularly when consistency matters across larger jobs. The key is calibration. Do not assume the dial setting automatically gives the exact percentage you think it does at the nozzle. Hose length, flow rate, pressure, viscosity and setup can all affect real-world performance.
Practical Examples of Correct Softwash Mixing
Example 1: Light Algae on a Rendered Wall
A facilities manager asks for green algae removal from a rendered commercial wall. The surface is sound but close to planted beds and pedestrian access. A sensible approach may be a lower-strength solution, appropriate surfactant, controlled application and careful plant protection rather than an aggressive mix.
Best practice would include:
- Test patch in a discreet area
- Pre-wet nearby plants
- Use controlled low-pressure application
- Prevent overspray onto windows, metal signage and passers-by
- Allow correct dwell time without letting solution dry harshly on the surface
- Rinse or post-treat according to product and site requirements
Example 2: Block Paving with Heavy Organic Growth
A domestic driveway has heavy green growth and black spotting in shaded areas. The contractor may use a stronger mix than on delicate render, but only after checking drainage, nearby lawns, edgings, metal features and any previous sealant.
On paving, the most common error is applying too much solution too quickly and allowing it to run into planted areas or drains without control. Accurate mixing is only half the job. Application control is just as important.
Example 3: Roof Treatment After Moss Removal
Roof work introduces additional risks: working at height, gutter discharge, overspray, neighbouring properties, water butts, conservatories, leadwork and sensitive landscaping. A roof softwash solution should never be treated as “just a stronger patio mix”.
Professional roof treatment requires a planned method, suitable access equipment, run-off management and clear customer communication. If you are not trained or competent to work at height and manage the chemical risks, do not attempt it.
Common Softwash Mixing Mistakes
Guessing the Mix
“A splash in a barrel” is not professional softwashing. Guesswork leads to inconsistent results, surface damage and poor pricing. Measure chemical and water properly every time.
Confusing Tank Strength with Application Strength
If you batch mix a 3% solution and apply it directly, your tank strength and application strength may be similar. If you use an injector, the chemical is diluted as it is applied. That means the tank strength is not necessarily the same as the on-surface strength.
Using Too Much Chemical
More chemical does not always mean a better clean. It can increase risk to plants, metals, clothing, seals, coatings and the operator. It also increases cost and may create avoidable odour issues.
Adding Random Detergents
Do not add washing-up liquid, traffic film remover, acids, degreasers or unknown additives to a softwash mix. Use compatible products only. If you do not know whether products are compatible, do not mix them.
Ignoring Dwell Time
A weaker solution with proper dwell time can often outperform a stronger solution that is rinsed too quickly. Softwashing is about controlled chemistry, not panic application.
Failing to Protect Plants and Metals
Plant protection is not optional. Pre-wet, cover where appropriate, divert run-off, rinse thoroughly and monitor vulnerable areas. Metals such as aluminium, copper, brass, zinc and lead can also be affected by incorrect chemical use.
Softwash Safety and Compliance Notes for UK Users
Anyone mixing softwash chemicals should understand the legal and practical responsibilities involved. In the UK, professional users need to consider COSHH, PPE, product labelling, safety data sheets, environmental protection, manual handling, public safety and working at height where relevant.
At minimum, you should:
- Read and understand the product label and safety data sheet before use
- Carry out a risk assessment for the site
- Wear suitable PPE for mixing and application
- Keep chemicals in original or clearly labelled compatible containers
- Prevent unauthorised access to chemicals and equipment
- Never mix incompatible chemicals
- Control run-off and protect drains, ponds and watercourses
- Store sodium hypochlorite away from heat, sunlight, acids and metals
- Transport chemicals securely and in line with applicable requirements
- Have an emergency plan for splashes, spills and accidental exposure
The best contractors build safety into the job from the start. They do not treat compliance as paperwork to complete after the event.
How Weather Affects Your Softwash Mix
Weather has a major effect on how softwash solutions perform. A mix that works well on a cool, overcast morning may behave differently on a hot, windy afternoon.
- Hot weather: solutions dry faster, increasing streaking and surface risk. Lower strength, smaller sections and controlled rinsing may be needed.
- Cold weather: chemical action can slow down, requiring more dwell time and realistic customer expectations.
- Wind: overspray risk increases significantly. Delay the job if you cannot control drift.
- Rain: light dampness may help pre-wetting, but heavy rain can dilute the solution and cause uncontrolled run-off.
- Direct sunlight: can accelerate drying and reduce control, especially on render and cladding.
Good softwashing is not just about the formula in the tank. It is about adapting the method to the site conditions.
Mixing Checklist for Contractors and Facilities Teams
Use this simple checklist before mixing a softwash solution:
- Identify the surface and contamination correctly.
- Check whether the surface is suitable for the proposed chemical.
- Read the product label and safety data sheet.
- Calculate the target strength using the correct stock strength.
- Measure water and chemical accurately.
- Add water first, chemical second and surfactant last if required.
- Label mixed solution clearly if it is not used immediately.
- Protect plants, metals, drains, ponds and neighbouring property.
- Apply at low pressure with controlled dwell time.
- Rinse, neutralise or post-treat only where appropriate and product guidance allows.
- Dispose of waste and residues responsibly.
- Record what was used, especially on commercial or managed sites.
Why Training Matters When Mixing Softwash Chemicals
Most softwash problems come from poor judgement rather than poor products. The operator chooses the wrong strength, fails to test the surface, overlooks drainage, mixes incompatible chemicals or applies in unsuitable weather.
Professional training helps contractors understand not only what to mix, but why, when and how to apply it safely. It also helps facilities managers and property maintenance teams ask better questions when appointing exterior cleaning contractors.
If you want to see how professional softwashing training is structured before committing to the full programme, you can try selected lessons from the SoftWash UK course for free. It is a useful way to preview the training and understand the standards, safety thinking and practical approach behind professional softwashing.
Frequently Asked Questions About Mixing Softwash Solutions
What order should I mix softwash chemicals in?
Add clean water first, then the measured chemical concentrate, then an approved surfactant or additive last if required. This reduces splash risk and helps the solution mix more evenly. Never mix unknown or incompatible chemicals.
How do I calculate a 3% softwash mix from 15% sodium hypochlorite?
Use the formula: target strength ÷ stock strength × final volume. For 20 litres of 3% solution using 15% sodium hypochlorite, calculate 3 ÷ 15 × 20 = 4 litres of sodium hypochlorite. Add this to 16 litres of water to make 20 litres total.
Can I use washing-up liquid as a softwash surfactant?
No. Washing-up liquid is not designed for professional softwashing and may cause compatibility, foaming, rinsing or residue problems. Use a surfactant intended for softwash applications and follow the manufacturer’s dosage instructions.
Is a stronger softwash mix always better?
No. A stronger mix can increase risk and cost without improving the result. The correct approach is to use the weakest effective solution, combined with suitable dwell time, surface testing and controlled application.
Can I store mixed softwash solution for later use?
It is better to mix only what you need. Diluted sodium hypochlorite solutions can lose strength over time, particularly when exposed to heat and sunlight. If a mixed solution must be stored temporarily, it should be in a compatible, clearly labelled container away from incompatible materials and unauthorised access.
Do I need different mixes for roofs, render and paving?
Yes. Different surfaces require different strengths, methods and risk controls. Roof treatments, render cleaning and paving restoration all involve different surface risks, drainage issues and application techniques. Always survey the site and test before full application.
Conclusion: Correct Mixing Is the Foundation of Professional Softwashing
Mixing softwash solutions correctly means more than adding chemical to water. It requires accurate calculation, surface knowledge, safe handling, suitable equipment, environmental care and professional judgement.
For contractors, the benefits are clear: better results, fewer callbacks, safer working, lower chemical waste and stronger customer confidence. For facilities managers and property maintenance teams, understanding correct softwash mixing helps you assess whether a contractor is working responsibly or simply guessing.
Start with the surface, choose the right chemical, calculate accurately, add water first, apply with control and never ignore safety documentation. If in doubt, reduce the risk, test first and seek proper training before taking on more complex work.
SoftWash UK supports the exterior cleaning industry with professional chemicals, equipment, safety resources and training for contractors who want to work to a higher standard. To explore suitable products and equipment for your next project, visit SoftWash UK and continue building your knowledge through practical, responsible softwashing education.
