Roof Washing

Why high pressure is wrong for tile roofs

Concrete and terracotta tiles have a protective surface coating applied at manufacture (pigment, sealant, or both) that gives the tile its colour and water resistance. High-pressure washing strips this coating, which leaves the tile body exposed to UV and water ingress, accelerating wear. Lichen rhizines also penetrate this coating layer, so removing lichen by force pulls the coating off with it. Soft wash uses a biocide solution that kills the lichen and algae at the cellular level, dwells for 20 to 40 minutes, then rinses off cleanly without touching the protective coating. The roof keeps its sealed finish and the lichen is genuinely gone rather than just visually removed.

Soft wash chemistry for roofs

Roof soft wash uses a stronger sodium hypochlorite concentration than house wash, typically 4 to 8 percent, because lichen and moss have a thicker cell wall than the surface mould on walls. We pair it with a surfactant designed to cling to sloped surfaces so the solution does not run off before it can work. Dwell time is longer than a house wash, around 20 to 40 minutes, and we re-treat heavily affected sections rather than trying to do everything in one pass. The post-wash biocide treatment is a residual chemistry that suppresses regrowth for 18 to 24 months by preventing spores from germinating on the freshly cleaned surface.

Tile, Colorbond, concrete, decramastic: by roof type

Terracotta tiles need the most cautious approach because the surface is porous and the pigment is integral to the colour. Heavy lichen can leave a faint shadow on terracotta after cleaning where the rhizines penetrated deeply. Concrete tiles are more robust and handle slightly higher pressure, but we still avoid raw high pressure on the tile body. Colorbond responds excellently to soft wash because the colour-bonded paint finish is sealed and chemistry-resistant. Colorbond roofs typically come up like new. Concrete decramastic roofs (the chip-coated style common on 1960s-70s homes) need the gentlest approach because the chip surface can be dislodged by pressure. Slate roofs are uncommon on Brisbane homes but when we encounter them we use the lowest pressure and a neutral chemistry to avoid affecting the slate finish. Trapezoidal corrugated iron and standard galvanised sheeting both clean well with soft wash. Older galvanised that has started to rust along the seams gets a degreaser pre-treatment but the rust itself we cannot reverse. We will tell you upfront if the rust is a structural concern rather than cosmetic.

Lichen vs moss vs algae: what's actually growing

Lichen is a symbiotic organism: a fungus growing in partnership with an alga. It appears as round or branching grey-green crusty patches and grows extremely slowly (a few millimetres per year). On Brisbane roofs it usually first appears on the south and west slopes that miss direct sun. The rhizines anchor into the tile pores, which is why force removal pulls coating off with it. Soft wash chemistry breaks the symbiotic relationship and kills both organisms at once. Moss is a simple non-vascular plant that grows in moist patches: around screws, in valleys, under overhanging trees. It is faster-growing than lichen but more easily removed because the anchoring is shallower. Algae is single-cell organisms that form the flat black or dark green staining streaking down slopes. Algae is mostly cosmetic but is a strong signal the roof is staying damp for too long, which means lichen and moss will follow if untreated. All three respond to soft-wash chemistry; lichen takes the longest dwell and the most thorough treatment.

Access, safety, and walking on tiles

Most tile roofs from the 1970s onwards are strong enough to walk if you know where the rafters are. We use soft-soled boots, walk on the lower edges of tiles where they overlap with their neighbour, and avoid the ridge caps and valleys. Steep pitches require harness work, which adds setup time but is non-negotiable for safety. Where access is impossible (decramastic roofs we will not walk, very steep pitches, fragile tiles) we work from a ladder, an extension wand, or a long-reach pole. We never compromise on roof access safety. A slip on a roof is one of the most serious accidents in our trade. Properties with double-storey or steep pitch get an access surcharge that we disclose in the quote, typically 15 to 25 percent on the base figure.

What to expect on the day for a roof clean

Roof cleans are full-day jobs on a single-storey home, two-day jobs on a larger or steeper property. We arrive with the truck-mounted system, an extension ladder, harnesses if needed, and the chemistry mix already prepared. The first 30 minutes is setup: protecting downpipes (so chemistry does not pool into them), pre-wetting plants and beds, and walking the roof to plan the sequence. The clean itself is two phases: chemistry application from the bottom up across the whole roof, then a long dwell (20 to 40 minutes) while we set up the rinse, then top-down rinse on a careful schedule so no section dries before being rinsed. After the rinse, the biocide post-treatment is sprayed lightly and left on. Gutters are flushed after to confirm the rinse moved through cleanly. Total time on-site is usually six to eight hours for a single-storey roof. You can be home or out, and most customers leave us to it.

Recommended cadence by roof type and suburb

Tile roofs in Brisbane benefit from a clean every 2 to 3 years. Suburbs with heavy tree canopy (Bulimba, Carindale, Belmont, Kedron) trend toward the 2-year end because lichen pressure is higher. Open-canopy suburbs (Aspley, Mansfield, Sunnybank Hills) can stretch to 3 years. Colorbond roofs need a clean every 3 to 5 years because the sealed finish prevents lichen from anchoring as deeply. Bayside roofs (Wynnum, Manly) need attention every 2 years regardless of material because salt accelerates the surface staining. We send a reminder when each customer is approaching their next recommended clean.

DIY roof cleaning: why we don't recommend it

Roof work is the highest-injury area in trades and DIY cleaning. The risks are not just a slip and fall (although that is the main one). The second risk is the technique itself: high-pressure DIY cleaning strips the tile coating, which accelerates the deterioration the customer was trying to prevent. The third is the chemistry. Consumer-grade roof-clean products are weaker than commercial chemistry and often need multiple applications, with each application increasing the chance of run-off into the wrong places. The fourth is the biocide post-treatment; without it, lichen returns within months. If you are confident on a roof and you have the right access equipment, DIY is possible for light algae. For anything involving lichen, moss, or any tile roof older than 10 years, the professional call is the right one. The cost difference is not large; the safety difference is.

Roof cleaning vs roof restoration

Roof cleaning is what we do: soft-wash removal of growth and grime, with a biocide post-treatment. Roof restoration is a different trade involving repainting or resealing the tile surface, typically by a roofing contractor. The two are sometimes confused because the visual result of a restoration is even more dramatic than a clean. A clean returns the roof to its existing surface condition. A restoration adds a new coating layer. If your roof is sound and the lichen/moss is the issue, cleaning is the right job. If the tile coating is failing (chalking, pitting, faded irregular colour), restoration may be the better call. We can recommend a roof restorer if you need one after the clean. We work alongside several in Brisbane.

What's included

• Soft-wash technique safe for tile, Colorbond, and concrete roofs
• Lichen, moss, and algae removed at the source, not just surface
• Post-wash biocide treatment to slow regrowth for 18-24 months
• Restores original colour without stripping tile surface coating
• Includes pre-wet plant protection and runoff management
• Gutter clearing available as an add-on in the same visit
• Before-and-after photos with every job

Roof Washing by suburb

Detailed roof washing guidance for the suburbs we work in most often. Each page covers local housing stock, common concerns, and pricing notes specific to that area.

Frequently asked questions