My wife was burning wood in the chimenea and overloaded it resulting in burning wood falling out onto the patio where she left it until it burnt itself out.
Now we have burn makes that won't shift with a powerwasher.
I've had a google and there a number of ideas and chemicals such as baking soda and sugar soap but I think this will need something seriously powerful to shift this. Being riven sandstone and not smooth then maybe mechanically removing it?
Any ideas?
I'd go for a straight swap - take up the worst affected flags and replace with new.
You could spend a small fortune on various chemical attempts, each making little or no difference, not to mention your time, and any attempt at mechanical cleaning will disfiugure the flags, relative to their neigbours.
