Soot outside fireplace, cleaning?

[wildwildwest]

I'd like to get the soot off before our new insert. The black on top is soot behind and above the old shroud (see the old insulation on the top left for height). What can I use? : water & dish soap? I was hoping to avoid tsp. What are your thoughts on Paint & Peel? Whats the correct term for this, it's superficial flagstone cuts stacked to look like brick.



Thanks for any thoughts!

 

[bholler]

paint and peel works amazingly