Why a pressure-only roof clean leaves the mould stripes back within a season, how a roof-safe soft-wash kills growth at the root, and which one your roof on this coast actually needs.
Short answer: Soft-wash for roofs, render and painted surfaces, pressure for hard surfaces like concrete. A soft-wash kills the mould at the root so it stays clean for years; a pressure-only clean strips the top and the stripes come back within a season.
Pressure cleaning is fast and it looks dramatic, which is why so many operators reach for it on everything. The problem is what it leaves behind. On a roof, mould and lichen send roots into the porous surface of the tile or the coating. A high-pressure blast knocks the visible growth off the top but does nothing to the spores in the pores, so the first wet season brings the dark stripes straight back. Worse, the pressure abrades the surface itself: Colorbond chalks, the protective coating on a recoated roof thins, and painted timber bargeboards split. You pay to make the roof look clean for a few weeks and shorten its life in the process.
A soft-wash flips the order. First a roof-safe biocide is applied and left to dwell, which breaks the mould, lichen and algae down at the root rather than just removing the part you can see. Then a low-pressure rinse carries the dead material away without ever abrading the surface. The result is a roof that stays clean for two to three years instead of two to three months, with no damage to the tile, the coating or the paint. The same logic applies to render and weatherboard walls: the right detergent breaks the growth and a gentle rinse takes it off, so the paint stays exactly where it was.
The honest answer is that both have a place, and the skill is matching the method to the surface. Soft-wash belongs on roofs, render, weatherboard, painted brick and any finish-sensitive surface. Pressure, used with the right nozzle, belongs on concrete driveways, paving and exposed aggregate. An operator who uses one tool on everything is making your surfaces fit their gear, which is backwards. On this coast, where salt and humidity speed up regrowth, getting the method right is the difference between a job that holds and one you pay for twice. If you are not sure which your roof needs, that is what a free walk-around or a photo check settles. Send a few photos or give us a call and we will tell you straight whether you need a clean, a restoration, or just to leave it a while longer.
Coastline Restoration Co.