Most of the products I see advertised turn out to be bleach in various concentrations...are there any products that really do restore sandstone paving to its former glory?
I could be wrong but I do not think you will ever get sandstone paving to look like it did when it was new..... I cleaned mine with good old soapy water and a scrubbing brush year before last, not a massive area at all and it came clean but it had lost it's powdery newness, and it has started looking grubby already. I thought about trying a sealer but then this would dull it's looks anyway. How big an area do you have to clean.
Non bio own brand cheap washing powder mixed with hot water and stiff brush I used. Brushed about. Left for an hour and another brush then hosed off
I had sandstone put down 5 yrs ago. It still cleans up ok with a pressure washer but some marks like black spots can't be shifted. Or at least I've not found anything yet. Sealing with a good sandstone sealer does enrich the colour which has faded over time and makes the stone water repellent . The sealer is expensive and not that long lasting. Basically sandstone looks stunning when first laid but it's porosity does not make it very durable as a long term solution in my humble opinion! I wouldn't use it again.
Use a pressure washer with a deck cleaning rotary head, it will break away any loose bits from the sandstone, so don't do it too often.