Removing Rust Stains From Sandwash Surface

[Greenside]

Our verandah has been nicely sandwashed but some places have what looks like a rust stain emanating from a piece of aggregate in the surface. Digging them out isn't really an option as repair is tricky - anyone solved this problem or have a suggestion? Strong acid, maybe?

[Soutpeel]

I would think acid maybe your only option

[Kwasaki]

Easily removed using hydrochloric acid and water, protect yourself and others.

[Greenside]

Thanks. I'll drop some acid on them.