Guide · updated 26 September 2026
Softwash mix ratio chart
How many litres of sodium hypochlorite (SH) and water to put in the tank for the strength you want at the surface. Charts for 12.5% and 10% SH, starting strengths by surface, and a calculator.
The short answer: for a 1% mix, add 8 litres of 12.5% SH to 92 litres of water (8 L per 100 L). For any mix, litres of SH = tank litres × target % ÷ SH strength %, then top up with water.
Mix calculator
Add 16 L of SH and 184 L of water.
Starting strength by surface
These are the strengths at the surface that most operators start from. Growth, weather and the surface itself all change what works, so test a small area first and let the mix dwell before deciding it needs to be stronger.
| Surface | Strength at the surface | Notes |
|---|---|---|
| House washing: render, painted walls, weatherboard, Colorbond cladding | 0.5–1% | Light mould and dirt. Rinse windows and plants. |
| Brick walls and fences | 1–2% | Test first on coloured mortar. |
| Concrete paths, driveways and pavers | 1–3% | Stronger for black algae; keep it off lawn edges. |
| Timber fences and decks | 0.5–1% | Weak mix only: strong SH lightens and furs timber. |
| Colorbond and metal roofs | 1–2% | Short dwell, then rinse well. |
| Concrete and terracotta roof tiles | 3–6% | Heavy lichen and moss need dwell time as much as strength. |
Litres of 12.5% SH per tank
Litres of 12.5% SH to put in the tank; fill the rest with water. For example, a 3% roof mix in a 400 L tank is 96 L of SH and 304 L of water.
| Strength at the surface | 20 L tankSH to add | 100 L tankSH to add | 200 L tankSH to add | 400 L tankSH to add | 1000 L tankSH to add |
|---|---|---|---|---|---|
| 0.5% | 0.8 L | 4 L | 8 L | 16 L | 40 L |
| 0.75% | 1.2 L | 6 L | 12 L | 24 L | 60 L |
| 1% | 1.6 L | 8 L | 16 L | 32 L | 80 L |
| 1.5% | 2.4 L | 12 L | 24 L | 48 L | 120 L |
| 2% | 3.2 L | 16 L | 32 L | 64 L | 160 L |
| 3% | 4.8 L | 24 L | 48 L | 96 L | 240 L |
| 4% | 6.4 L | 32 L | 64 L | 128 L | 320 L |
| 5% | 8 L | 40 L | 80 L | 160 L | 400 L |
| 6% | 9.6 L | 48 L | 96 L | 192 L | 480 L |
Litres of 10% SH per tank
SH that has been sitting in the heat is often closer to 10%. The same mixes need more of it.
| Strength at the surface | 20 L tankSH to add | 100 L tankSH to add | 200 L tankSH to add | 400 L tankSH to add | 1000 L tankSH to add |
|---|---|---|---|---|---|
| 0.5% | 1 L | 5 L | 10 L | 20 L | 50 L |
| 0.75% | 1.5 L | 7.5 L | 15 L | 30 L | 75 L |
| 1% | 2 L | 10 L | 20 L | 40 L | 100 L |
| 1.5% | 3 L | 15 L | 30 L | 60 L | 150 L |
| 2% | 4 L | 20 L | 40 L | 80 L | 200 L |
| 3% | 6 L | 30 L | 60 L | 120 L | 300 L |
| 4% | 8 L | 40 L | 80 L | 160 L | 400 L |
| 5% | 10 L | 50 L | 100 L | 200 L | 500 L |
| 6% | 12 L | 60 L | 120 L | 240 L | 600 L |
Strength from an X-Jet with neat 12.5% SH
An X-Jet or proportioner dilutes whatever it draws. The strength at the surface is the bucket strength divided by the tip's ratio plus one. With neat 12.5% SH in the bucket:
| X-Jet tip | 11.4 L/min3 GPM | 15.1 L/min4 GPM | 18.9 L/min5 GPM | 22.7 L/min6 GPM |
|---|---|---|---|---|
| Black | 2.49% | 2.09% | 1.67% | 1.39% |
| Beige | 1.39% | 1.14% | 0.89% | 0.74% |
| Red | 0.96% | 0.74% | 0.6% | 0.5% |
| White | 0.54% | 0.4% | 0.32% | 0.27% |
| Blue | 0.44% | 0.33% | 0.27% | 0.22% |
From the printed X-Jet tip chart, interpolated for flow. For soap doses and other tips, use the X-Jet calculator.
Surfactant
Add a surfactant (soap) made to be stable in sodium hypochlorite. It helps the mix cling to walls and roofs and wet the growth evenly, and masks some of the chlorine smell. Dose it to its label: too much makes the mix foam in the pump and run off before it works.
Safety
- Wear eye protection, chemical-resistant gloves and clothing you don't mind bleaching.
- Wet plants and lawns before and after spraying, and rinse run-off away from gardens.
- Never mix SH with acids, acid-based cleaners or ammonia. The reaction releases toxic gas.
- Keep SH in its original container, out of the sun, and read the safety data sheet.
- Use pumps, hose and fittings rated for chlorine: polypropylene, 316 stainless and Viton seals.
Common questions
How much 12.5% SH do I add to make a 1% softwash mix?
Add 8 litres of 12.5% sodium hypochlorite for every 100 litres of mix, and make up the rest with water (92 litres). The formula is: litres of SH = tank litres × target % ÷ SH strength %. For 10% SH, add 10 litres per 100 litres for a 1% mix.
What strength SH should I use to softwash a roof?
Concrete and terracotta tiled roofs are usually cleaned at 3–6% sodium hypochlorite at the surface, depending on how heavy the lichen and moss are. Metal and Colorbond roofs need less, around 1–2%. Always test a small area and give the mix time to work before rinsing.
What strength should I use for house washing?
House washing render, painted walls and cladding normally needs 0.5–1% sodium hypochlorite at the surface. It is enough to kill mould and mildew without harming paint, and it rinses off easily.
How strong is the SH I buy?
Liquid sodium hypochlorite sold for pools and softwashing is usually 10% to 12.5% when fresh. It loses strength with heat, sunlight and age, so store it cool and shaded, buy only what you will use soon, and check strength with a test kit if a drum has been sitting.
How do I work out the strength coming out of an X-Jet or proportioner?
Divide the strength in the bucket by the ratio plus one. A tip drawing 1 part chemical to 10 parts water dilutes the bucket 11 times, so neat 12.5% SH lands at about 1.1%. The table on this page shows the result for common X-Jet tips, and the X-Jet calculator works it out for any tip and flow.
Can I mix SH with other chemicals?
Only with a surfactant made to be stable in sodium hypochlorite. Never mix SH with acids, acid-based cleaners or ammonia: the reaction releases toxic chlorine or chloramine gas.