Indian sandstone staining

[Rich H]

When I laid my first Indian Sandstone patio some years ago, I also rendered some nearby retaining walls. Even though I covered the paving, some mortar managed to migrate underneath onto one of the slabs.

After using the usual methods (boot, water, brush) I was still left with a spot, which I then decided to remove with brick acid ('Patio Cleaner').

I ended up with a bigger brown spot. This was a worthwhile lesson (I replaced the slab) in that the acid in the cleaner reacts with the ferrous sulphate naturally in the slab and creates ferrous oxide (rust!). Since then, I've been extremely careful about keeping the slabs clean but from time to time you can't help (or one of your labourers can't) getting something on them.

Does anyone know of an agent that will safely remove cement/mortar marks?

[Tony McC]

There's no non-acidic cement remover, but about 18 months ago, a contact at Bradstone told me they had a magic jollop that would 'reverse' the orangey-brown permanent stain that come from acid cleaning. He promised to send me details, but I'm still waiting, despite several reminders, both in person and by email.

I have seen Oxalic acid lighten the paler stains, but it doesn't remove the worst effects and is, in my iopinion, a waste of time and money, not to mention the fact that it's bloody nasty stuff to boot!

For anyone wanting to see just how awful acid-generated rust staining can be on these imported stone products, have a look at this page

[Rich H]

Thanks, Tony. Hadn't spotted that page before (you have so much info on this site!). I suppose the real answer is to keep them clean in the first place.