White chalky marks on outdoor tiles, glass and pool fencing usually come from one source: irrigation. A sprinkler head that catches the edge of a paved area or a window, left running all summer, deposits dissolved mineral every cycle.
Whether it comes off depends entirely on how long it has been happening.
Two stages
Deposit. Mineral sitting on the surface. It is physically on top and it can be dissolved or lifted off. Catch it in the first year or two and it is straightforward.
Etching. The deposit has reacted with the surface, or sat long enough to pit it. On glass the silica itself is corroded. On a glazed tile the glaze is damaged. This is not a stain and nothing removes it.
The test: run a fingernail across it. A deposit has a slight raised texture. An etch is smooth and in the surface — you can feel that there is nothing sitting on top, and yet the cloudiness is still there.
The fuller distinction on glass is in salt film vs hard water staining.
Sydney water is actually soft
Worth knowing, because it changes the diagnosis.
Sydney mains water is relatively soft by world standards, so classic hard-water scale is less of a problem here than in many cities. When we see heavy mineral deposits in Sydney, the cause is usually one of:
- Bore or tank water used for irrigation, which can be very hard and often carries iron as well
- Pool water splashing out, which is concentrated by evaporation and top-ups
- Salt rather than calcium, on a coastal property
- Efflorescence coming out of the tile bed or grout, which looks similar and is a different problem entirely
That last one matters. If the white bloom is coming from the joints rather than landing on the surface, it is efflorescence, and it means water is moving through the substrate. Cleaning it repeatedly treats the wrong thing.
Removing a deposit
On porcelain, glazed ceramic and glass: a mild acid — a dedicated mineral deposit remover, or diluted white vinegar for light marks. Apply, let it dwell, agitate with a non-scratch pad, rinse thoroughly.
On natural stone: no acid. Travertine, limestone, marble and sandstone all etch, and you would be trading a removable deposit for permanent damage. Use a dedicated pH-neutral mineral deposit remover for stone and accept a slower result.
This is the single most common way people wreck a stone pool surround — reaching for the product that works on the tiles.
On glass: a proprietary mineral remover, worked gently. Never a razor blade on toughened glass, and never an abrasive pad.
Restoring etched surfaces
Glass: light etching can sometimes be polished out with cerium oxide. It is slow specialist work and it is only worth it on large panes. Heavy etching is replacement.
Stone: etching is honed out, which means mechanically refinishing the whole area so it is consistent. Specialist.
Glazed tile: damaged glaze cannot be restored.
There is no product that reverses any of these, whatever the label says.
Prevention, which is the real answer
Move the sprinkler. Obvious and almost never done. Check where every head actually throws, not where it was aimed when installed — they drift, and a head catching a window or a stone edge will do it every single cycle for years.
Rinse after pool use on the coping and surrounds.
Squeegee glass that gets regularly wet, or at least rinse with fresh water.
Seal porous stone with a breathable impregnator, which reduces absorption — outdoor tile sealer.
Deal with it early. A deposit removed this year is a clean. The same deposit in five years may be an etch.
For cleaning, see how to clean outdoor tiles or window cleaning.
