Sandstone cleaning and sealing in North Manly

Most North Manly sandstone sits close to the ground: paved courtyards, garden paths, low front walls and edging around beds. That makes it more exposed to moisture from below than stone on a hillside. Paving near the lagoon and the reserves tends to show three things at once: a green or black film of algae and mould, a white crust of salt drawn up through the stone, and darker damp patches that linger after the rest of the surface has dried. Front walls on Pittwater Road add traffic grime. Our technicians trial products on a small area before starting, and they check how wet the stone is with a moisture meter.

We kill organic growth with a biocide made for masonry and natural stone, allowing time for it to work through the pores, then remove it with soft brushes and a light rinse. Salt bloom is swept off dry before any water goes near it. A turbo nozzle never touches the stone, because it erodes the surface and leaves it more open to water and salt than before. On flat ground, water pools rather than running off, so we clean in smaller sections, hold each one inside bunds and recover it by wet vacuum before moving on. Everything collected leaves the site with us, well away from the lagoon and its wetlands.

Whether to seal depends on the moisture reading. Stone that dries out properly between rain, such as raised steps, wall caps and well-drained paving, usually suits a breathable impregnating sealer that slows growth and staining. Paving that draws water up from the ground should not be sealed, because the sealer stops moisture escaping and the salts it carries then break up the surface from inside. Where that is the case, we say so and suggest drainage improvements instead. For stone that is ready, you pick between natural and enhancing finishes from small trial areas, apply thin coats with no surface film, and keep a note of the product for later maintenance.