I have a question on fixing a concrete staining project. I had a contractor do some landscaping in my backyard and as he also stained the concrete (Used Behr semi transparent stain). About 30 mins after he finished the staining, it started raining and the stain washed away in patches. I still see few areas of stain, but the stain is not uniform across the concrete.

I was hoping the contractor would come back to fix the above and redo the concrete staining. I called the contractor several times and he is not responding my calls :(

I have decided to fix the above and redo the concrete stain myself.

Couple of questions:

1) Since the contractor did the prep work prior to applying the stain, do I still have to clean and etch the surface prior to applying the concrete stain? Or can I just wash the surface and let it dry without having to etch the surface?

2) Do I need to strip and remove the old coating OR just apply another layer on top of what was sprayed by the contractor?

Please advise, I am planning to finish this work in the next couple of days.