Never pressure clean asbestos cement
It's illegal in every state to use high-pressure water spray or compressed air on asbestos materials. ASSEA, the national asbestos agency, says pressure cleaning asbestos roofs has caused contamination costing hundreds of thousands of dollars to fix, with fibres spreading to neighbours' properties, footpaths, roads and stormwater. Queensland can fine homeowners up to $10,000 for water blasting asbestos cement. If your home was built before 1990, have the roof identified first with our asbestos checker and the guide is my roof asbestos?.
When a roof clean is worth paying for
Before painting or restoring. Coatings don't stick to dirt, moss or chalky old paint, so a clean is always the first step of a roof painting job.
When moss and lichen are taking hold. They shed debris into gutters and valleys, where it blocks the flow. Our page on moss and lichen removal goes deeper.
If the roof feeds a rainwater tank. A cleaner roof means cleaner water, as long as the tank is disconnected while the roof is washed.
When you're selling. A clean roof looks better from the street. Just don't expect it to hide cracked tiles from a building inspector.
Pressure cleaning or soft washing?
| Pressure cleaning | Soft washing | |
|---|---|---|
| How it works | High-pressure water blasts off dirt, moss and the loose surface | A cleaning or moss-killing solution goes on at low pressure, then it's rinsed |
| Suits | Concrete tiles about to be recoated, heavy build-up | Older or fragile roofs, terracotta, light to moderate growth |
| Main risks | Cracks brittle tiles, forces water under tiles, strips faded colour coats | Runoff into gardens and tanks if it isn't managed, slower results |
| Afterwards | Concrete tiles may look patchy until they're recoated | The surface is left much as it was |
What can go wrong
Tile makers are wary of high pressure. Monier strongly advises against pressure washers on roof tiles because of the risk of damage, and recommends a professional roof cleaner instead.
Water going where it shouldn't is a common problem. A lance aimed up the slope drives water under tiles, laps and flashings, and the first you know about it is a stain on the ceiling.
Old tiles also crack underfoot, and the cracks may not show until the next heavy rain, so a careful roofer checks for breakages and replaces them before leaving. On metal, ask which cleaner they'll use, because BlueScope says sugar soap and some other cleaners shouldn't be used on bare ZINCALUME.
Mess counts too: slurry on walls, windows, cars and the neighbour's washing. Ask how it'll be contained.
Questions to ask before you book
- Will you pressure clean or soft wash my roof, and why?
- Is the moss being treated as well, and with what product?
- How will you protect my rainwater tank, solar panels, windows and garden?
- Who clears the gutters and downpipes after the clean?
- If a tile cracks while you're working, will you replace it, and at what cost?
- What's your licence number, and can I see your insurance?
What you can do, and what needs a roofer
You can
- Trim back branches that shade the roof or drop leaves on it
- Clear gutters from a ladder, if you're comfortable and can reach safely
- Check whether the roof could be asbestos cement before booking anyone
- Move cars and cover outdoor furniture on cleaning day
Leave to a roofer
- All pressure cleaning and soft washing. A hired pressure washer, a ladder and a slippery roof are a quick way to get badly hurt
- Moss and lichen treatment on the roof
- Replacing any tiles cracked during the clean
- Any roof that might contain asbestos
Where we'd start
If you're cleaning ahead of a repaint, have the same roofer do both, so the clean is done with the coating in mind. If you only want the moss gone and the roof is otherwise sound, ask about a soft wash and treatment instead of a full blast, especially on older tiles. And if the roof is old fibro, don't book a clean at all until it's been identified.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.
Finding a roof cleaner near you
Roof cleaning is done by roofers, roof restorers and some specialist cleaning businesses. Send us your job and postcode, and we'll pass it to one licence-checked roofer who covers your area. They'll be in touch to arrange a time to look.
The decision to go ahead is yours.