I Had a similar problem it was iron product so i rang marshalls technical advice and they told me there was not alot i could do but try 1 in 10 mix of brick acid. sand stone quickly sucks in the product.
hope this helps.
What Phil says is the most likely outcome. All natural stone has traces of iron in and it is just a case of the oxidisation process bringing it out. When we started out in the stone business, as well as stocking our own products we would also display some global stone products. We installed some of their yellow glory limestone at our showroom and after a couple of weeks we were horrified to see that there were rust patches everywhere. After 4-5 weeks it was gone.
I would not worry about it. It will just rust away with time.
All the best
phil smith said:
it could also be that the stone already had traces of iron in them when they were mined, and now they have been laid and they have been out in the elements of our weather they are naturaly going rusty.
the good thing about sandstone is its fairly easy to clean. If it is a surface lichen then a good scrubbing off with either a wire brush, or stiff broom and damp sharp sand works wonders. personally i try and avoid any chemicals on sandstone as it can cause so much immoveable damage
try eco-chem biodegradable moss & algae remover spray.......
if not jet wash lightly?
fail: relay new replacement slabs :)