Rust on Flagstone
by Mike Siegel
(Geismar, LA - USA)
I recently installed a flagstone patio and walkway in my yard. The stone is blue/gray color and has a fast absorbtion rate. It is not acid sensitive as it does not "fizz" when muratic acid is applied (even full strength).
The problem I am having is that some of the stone has a reddish "rust" colored tint that I would like to remove. Some of the rust is somewhat loose (like dirt or sand) and can be removed with a brush and water, while other parts appear to be permanently rust stained and the stains can't be removed. Muratic acid has little effect on the rust color. This project is not grouted in - it is in a sand and limestone base with aggregate between the stones.
I would like to remove this rust color for the most part and then seal the stone to maintain a wet look that is not slippery. Some rust color enhances the look of the patio, but some stones are 100% rust red color. Do you have any ideas on how to remove the rust stains?
I attached pictures for clarity. I have scrubbed these stones with a brush and muratic acid solution up to 50% acid/water solution.