pressure cleaning

I'm quite new to pressure washing and a customer has some spots of tar on a some of the sandstone papers, any ideas for a good product/method to get this off please. It has just been laid so is covered in a layer of dried concrete residue, would a hypo wash sort this out beforehand or just...

Hope you can help me. I have problem with left striping after cleaning. I have tried to change the way of wand moving when cleaning, distance from surface but with no results. I am using Honda Gx 200 3000psi and 12 lpm with 030 nozzle. Any suggest what to change or what should I do? Pictures...