Can anyone give me some tips on how to clean up sandstone. The pillars in our bay window and directly below the iron gutter is looking black in places. Also, how best to remove old exterior paint (oil based) from the external window sill? Thanks for your help[/b]
I'd make a start on the sandstone by using a bit of elbow grease + scrubbing brush + water on a test patch. Remembering, of course, to keep changing the water.
As for the paint - there are lots of products available. You can choose between the liquid sort (N*****ors?) or a poultice system like Peelaway.
Others will now pop out of the woodwork with much more detailed and expert suggestions, but at least your question has slid back to the top of the list.
There are a number of ways to remove old oil paint depending on how stuck it is and how likely it may be to have lead in it.
If you suspect lead then sanding and hot air stripping are to be avoided if possible and use dust protection anyway - if that's the case then nitromors or a poultice will be best. Personally I found nitromors to be an expensive way to turn old paint into sloppy mess that stayed stuck but others have had success and recommend it - I guess it depends on the paint you won't know unless you test.
My builders also used dry scraping - pulling a wide sharp chisel backwards over the lose paint to cause it to flake and crack then finishing up with a hand sand.
I've done a lot with a hot air gun which is pretty effective - dangers are scorching the wood (no problem if you're repainting) or melting lead paint fumes.
Then finished up with an orbital hand sander or by hand.
If you want to repaint then you may only need to remove lose paint and key with a hand sand
When I bought some sandstone hinge blocks for my gate piers recently, I asked the mason at the quarry about the best way to clean sandstone. He recommended carefully rubbing it with another piece of sandstone - which, when you think about it, does rather make sense. He cut me a piece about the size of a normal cork sanding block to do this with.
So far I've only used it on new stone - to remove some mortar staining but mostly to remove the crayon that the quarry used to label the blocks! - and it works fine on that.