Sandstone copping stones cleaning

[Craig24]

I’ve previously jet washed the coping stones (sandstone?) at the front of my house. Unfortunately they haven’t really cleaned as well as I’d of hoped. I used household bleach, scrubbed them and then jet washed them.

The black marks just won’t budge. Any tips of anything else I could use / try?

 

[Wayners]

Non bio washing powder and water with a scrubbing brush.
Or
Buy a specific cleaner online

 

[Charlie George]

Sodium hypochlorite is much stronger than normal bleach.

https://www.amazon.co.uk/JOVS-Sodium-Hypochlorite-Liquid-Chlorine/dp/B091M9XR9S/ref=asc_df_B091M9XR9S/?tag=googshopuk-21&linkCode=df0&hvadid=514530792441&hvpos=&hvnetw=g&hvrand=5687124825152270229&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046626&hvtargid=pla-1234928975405&psc=1&mcid=e488720f887c315fb683e55c0b49b9c5

 

[Wayners]

Didn't think that was ok on sandstone.
Nor vinegar

 

[jj4091]

I would not bother if I were you sand stone absorbs moisture and it will just get contaminated again in a relatively short space of time as you have already found from previous cleaning. The only thing that might improve it is one of those lances for your washer that increases the pressure and rotates the jet at the same time.

 

[Craig24]

Thanks. That’s the type of lance I used already. So sodium hypochlorite is a no go?

 

[Odds]

The stones are already weathered and worn, so using SH now would only advance the wear and tear.
Soap n' water then a stiff brush would get the grit out but don't go too far in your quest. Elbow grease, and plenty of it, is your best bet.