Cleaning sandstone

Anyone know how I would get my sandstone window sills cleaned ?

I have tried brick cleaner, a stone foam cleaner and pressure washing but none have shifted the black soot and grim off them

You can have them sandblasted,but it sounds like you have the grey millstone grit type so they will be a dark grey colour.

Wire brush?

A solution made up with caustic soda (sodium hydroxide) which can be bought from a chemist or wilko. Cant remember the actual dosage though and as with stuff like this wear goggles and protective gloves etc.

Have you sorted it out yet? I used thick bleach on my patio stones and it worked. They had been really black with dirt before. I'd tried a water pressure blast but it hadn't worked. I applied the bleach with a wet hand brush and then spread it out a bit. Wear goggles and protective gloves etc. You then have to give the process about half an hour and monitor it. When they are clean wash the bleach away with plenty of water, taking care with where it goes. All this is at your own risk of course.

Evening all, I found a company That came and painted on a chemical and then hot pressure washed it off, come up great

I'll vouch for the bleach idea, did exactly the same with mine 2-3yrs back. Couldn't believe how well they came up. The worst one needed a couple of attempts and a once over with a stiff wire brush. But well worth all the effort. I've since used bleach for ALL outdoor cleaning tasks. I usually buy thick bleach in 1 gallon containers.

I would certainly give it a try before lining someone else's pocket.

Evening all, I found a company That came and painted on a chemical and then hot pressure washed it off, come up great ��

Glad its sorted but what chemical was used?