Rust marks in limestone

[MatthewC]

My house has quite a few nasty brown streaks due to embedded steel/iron in the walls. Does anyone know how to get rid of these marks without damaging the limestone? I guess where there is metal visible I could use jenolite or equivalent, but I'll have to test it somewhere inconspicuous first. However, the really visible brown marks go a couple of feet down the wall and I'm nervous about doing anything irreversible.

Ideas/experience please?

Matthew

 

[Keithj]

Gentle, careful work with oxalic acid.

 

[mardinor]

Be careful with acid on limestone!

Try Rust-ex from Lithofin. Designed to do exactly this job on stone that is sensitive to acid (such as limestone).
I used it to remove similar brown marks from marble.
I have a bottle left if you want to try it, and am just down the road from you. PM me if interested.