Pressure Washing Chemicals: What's Used & Is It Safe?

If a pressure washing operator tells you they don't use any chemicals — just water — they're either misleading you or doing a job that won't last past the next rain.

Real pressure washing and soft washing relies on chemistry. The water removes; the chemistry kills the things that grow back. Both matter. Here's exactly what's in the bottle, what each one does, why it's safe when used correctly, and what to ask before you book.

The three core chemicals

Most legitimate Sydney operators use the same handful of products. Brand names vary, base chemistry doesn't.

1. Sodium hypochlorite

What it is: the active ingredient in pool chlorine and household bleach. We buy it in 12.5% concentration (commercial grade) and dilute it down for spraying, usually to 1–4% depending on the surface and the severity of staining.

What it does: kills algae, mould, mildew, lichen, gloeocapsa magma (the black streaks on roof tiles), and the green wash on shaded render walls. This is the chemistry that makes a soft wash last. Pressure-only cleaning blasts the surface dirt off; sodium hypochlorite kills the colony so it doesn't grow back in eight weeks.

Where we use it: roofs, render, painted brick, fibre cement, eaves, fences, anywhere with biological staining. Pre-treatment on driveways and paths before the rotary cleaner pass.

Dilution rates we typically run:

• Roof tiles: 3–4% (heavy biological load)
• House render and walls: 1–2% (lighter load, gentler on plants)
• Driveway pre-treatment: 2–3%
• Light surface mould: 0.5–1%

2. Alkaline degreasers

What it is: a high-pH cleaner, usually based on potassium hydroxide or sodium hydroxide with surfactants. Ours runs around pH 12–13 in concentrate, diluted to pH 10–11 in use.

What it does: breaks down oils, grease, traffic film, exhaust deposits, and the embedded grime that water alone won't shift from a driveway or garage floor. It's what gets motor oil out of concrete pores and tyre marks off pavers.

Where we use it: garage floors, driveways with vehicle stains, commercial loading zones, restaurant kerbs. Not on render or painted surfaces — alkaline cleaners can lift paint at higher concentrations.

3. Surfactants

What it is: soap, basically — but engineered to be compatible with the active chemistry. Non-ionic surfactants for soft wash, anionic for degreaser blends.

What it does: reduces surface tension so the chemical actually wets and clings to vertical surfaces long enough to do its job. Without surfactant, sodium hypochlorite sprayed on a vertical wall runs off in 20 seconds. With surfactant, it dwells on the surface for 5–15 minutes — enough time to kill the biological growth.

This is the bit that separates a real soft-wash setup from someone with a pump sprayer full of pool chlorine. Surfactant choice is also where allergen concerns come up, so we use products with full SDS (Safety Data Sheets) available on request.

What about acids?

You'll see some operators using muriatic acid (hydrochloric acid) for rust stain removal or efflorescence on brickwork. It works, but it's aggressive. We avoid it where possible — modern oxalic-acid-based rust removers do the same job with much less risk to surrounding plants and finishes. If a job genuinely needs acid (deep efflorescence on a sandstone wall, for example) we'll quote it specifically and explain the trade-offs.

We never use acid for general cleaning. There's no shortcut there worth taking.

"Eco-friendly" and "chemical-free" claims

Be sceptical. Truly chemical-free pressure washing exists and it's used in heritage applications where chemistry would damage delicate stone — but for a residential driveway or roof clean, "no chemicals" is code for "pressure-only", which means the staining returns within a season.

There are better and worse chemicals. Sodium hypochlorite at proper dilution, applied correctly, broken down by sunlight and water within hours of application — that's not the same risk profile as a heavy-metal fungicide. The stuff we use is, fundamentally, dilute pool chlorine plus soap.

Safety: plants, pets, kids

The real-world questions every customer asks. The honest answers:

Plants. Sodium hypochlorite at house-wash concentration can burn foliage if it lands on the leaf and isn't rinsed off. Our process is to wet down all garden beds and shrubbery within 2 metres of the work area before we start, then rinse them again after. Wet leaves dilute the chemical on contact and we've not had a plant casualty in years using this method. Sensitive plants (azaleas, ferns, anything with very thin leaves) we'll cover with drop sheets if they're directly in the spray path.

Pets. Keep pets indoors during the work and for an hour after. Once the surfaces are dry and rinsed, the residual chemical breaks down rapidly in UV. Pet-safe by the time the crew packs up. We've cleaned thousands of properties with dogs in the next room and never had an issue.

Kids. Same as pets — indoors during work, fine after surfaces are dry. The post-clean residue is essentially the same as a chlorinated swimming pool, which is to say negligible. We always rinse three times more than the chemistry strictly needs, partly for finish quality and partly to leave nothing behind.

Drinking water tanks. If the property has rainwater tanks plumbed off the roof, divert before a roof clean. Always.

Dwell time and rinsing — where the craft is

Chemistry isn't dump-and-blast. The skill is:

• Mixing rate — too weak and you waste a trip; too strong and you risk surface damage or plant damage.
• Application pressure — soft wash chemicals go on at under 500 PSI through a chemical injector or dedicated soft-wash pump. High pressure aerosolises the chemical and that's a respiratory issue for the crew.
• Dwell time — 5 to 15 minutes typically. Watch the staining lighten in real time. Too short and the chemistry hasn't done its job. Too long on a sunny day and the surfactant dries out and leaves a residue.
• Rinse volume — proper rinse is at least double the volume of chemical applied, with a low-pressure clean-water pass. This is where shortcut operators cut corners.

A crew that can articulate all four of those things on the job is a crew that's done it before. A crew that says "yeah we just spray it on and pressure wash it off" is a crew that's about to damage something.

What to ask before you book

If you've got plants you care about, kids, pets, or a tank — ask:

1. "What chemicals will you be using and at what concentration?"
2. "How do you protect the garden beds during application?"
3. "Can you provide an SDS for the products?" (Any legitimate operator can, on request.)
4. "What's your rinse process?"

Vague answers = walk away. Specific answers = you've found a crew that takes the work seriously. We cover most of these on our FAQ, and the same products we use on every pressure washing and exterior cleaning job are documented with SDS available to any customer who wants to read them.

The chemistry is the part of pressure washing that actually delivers a 12-month result instead of a 12-week one. Skipping it is how operators come in cheap. Knowing how to use it is how a clean home stays clean.