Most roof cleaning advice online treats a roof as one surface. It is not. A glazed concrete tile roof and a Colorbond metal roof respond to cleaning in almost opposite ways, and the method that restores one will quietly ruin the other.
Tile roofs: the coating is the thing you are protecting
Most Brisbane tile roofs are concrete, finished with a factory coating that gives them their colour and seals the porous concrete underneath. That coating is what you are trying to preserve. Once it has worn through, the tile absorbs water, holds moisture longer, and grows lichen faster than before.
The failure mode is predictable. Someone puts a turbo nozzle on a tile roof, strips the coating along with the lichen, and the roof looks superb for a season before deteriorating faster than it ever did. Lichen is the real problem on tiles because it does not sit on the surface, it roots into it. Blasting the visible growth off leaves the root structure behind, and it returns within months.
The right approach on tiles is a treatment first, letting it kill the growth at the root, then a low pressure rinse to lift what is left. Slower, and far better for the roof.
Metal roofs: pressure is rarely the issue, chemistry is
Colorbond and Zincalume are more forgiving of pressure than tile, but far less forgiving of the wrong product. Strong alkaline cleaners will dull the paint finish permanently, and using an incompatible product can void a Colorbond warranty.
Metal roofs also collect a different kind of dirt. Rather than lichen rooting into the surface, you get a chalky oxidised film on older paint, tea staining near the coast, and a build-up of grime in the pans where water sits. That responds to a neutral detergent, dwell time and a gentle rinse.
The other consideration is the fasteners. Older metal roofs have screws with rubber washers that perish over time. High pressure directed at a perished washer will drive water straight into the roof cavity, and the owner finds out weeks later via a ceiling stain.
What the two have in common
On both roof types, direction matters more than pressure. Water driven upwards under the laps of tiles or sheets goes places the roof was never designed to send it. Every pass should work with the fall of the roof, not against it.
Both also need the gutters cleared afterwards. Whatever comes off the roof ends up in the gutter, and leaving it there creates the next problem.
Which does your roof need?
If you have concrete tiles with visible black or orange growth, you need a treatment-led roof clean, not a blast. If you have metal and the colour looks flat and chalky rather than dirty, you need the right chemistry and a soft wash rather than more pressure. Our guide to soft washing versus pressure washing covers where that line sits.
If you are unsure which you have, send us a photo. We clean both across Brisbane, from Everton Hills and Mitchelton through to Carindale, Birkdale and Shailer Park.
