Rust and streaks on outdoor stairs
Rust stains come from metal left on the stone, from railings and planters, from fertilisers or from iron in the stone itself. They are removed with a rust remover made for stone, and deeper ones with a poultice. Bleach does not work on rust and can set it.
Where rust on stone comes from
- Metal on the stone: planters, doormats with a metal frame, cans, nails. The stain then takes the shape of the object.1
- Railings and anchors that water runs off onto the steps.
- Lawn fertiliser that contains iron.
- Iron in the stone itself. Some granites and quartzites rust from within over time: the stains are irregular and follow the pattern of the stone.2
How to remove it
- Wash the surface with a pH-neutral cleaner and dry it.
- Apply a rust remover made for stone, following the instructions. These products turn iron oxide into a compound that can be rinsed away.2
- Wait the stated time, then rinse thoroughly with water.
A poultice for deep stains
The rust remover is mixed with absorbent powder into a paste, spread thickly, covered with plastic film and left for up to a day. As it dries, the paste draws the iron compounds out of the pores.2 Sometimes it needs repeating.
What not to do
- Do not use bleach: it does not work on rust and can set the stain.2
- Do not scrub with a wire brush, which leaves metal particles of its own.
- Do not reach for hydrochloric acid.
Prevention
Pads under planters, doormats without metal, railings with a drip groove, care with fertiliser near the stairs. When choosing stone for outdoors, ask whether the variety tends to rust.
(Sources)
-
Natural Stone Institute, Remove Stains from Stone Applications
-
Dynamic Stone Tools, Rust Stain Removal from Natural Stone: Step-by-Step
(Questions)
Can every rust stain be removed?
Not always. Deep, old rust can stay for good. The sooner, the better.
Will hydrochloric acid remove rust from granite?
It can damage the stone and the joints. Use rust removers made for natural stone.
