Sandstone steps stained by render

[mazoue]

I have have had a set of steps built in my garden with buff coloured sandstone treads. The risers have been rendered as have the walls either side of the steps.

The render used was K-rend in polar white. Unfortunately where the render has spilled onto the sandstone it has left a white stain. It is not clear how deep this stain has penetrated but it is certainly not just excess render on the surface.

I am reluctant to use an acid, such as brick acid, as I understand that this can react with the iron in the sandstone and produce another type of staining. I am also reluctant to use a jet power washer as it is not clear that it would work and I could damage the render.

Other than using sandpaper to remove the stained surface layer, does anyone know of a way of removing the stains from the sandstone?

 

[Alastairreid]

http://www.gosfordquarries.com.au/care-maintenance

 

[Micilin]

Try rubbing it with a piece of the same stone, wet.

 

[roughcaster]

It's very easy to say it, but it's "always" advisable to cover up any surface you don't want stained/marked when using cement etc,, especially window cills, steps, slabs, glass.

 

[MarkWG]

Media blasting with something like baking soda? Probably half way between power-washing and sandblasting, which will take back the surface (being as hard as the sandstone...)