I pointed out some dips in the corners to the guy who built my shower pan and his action was to add more mixture in the corners and drag it down. He did not smooth it out, or "screed" it, I believe is the correct term, so I'm left with a situation where the new mixture ends very roughly on top of his first attempt. He has stopped work for now, while I save up some more money to finish the job (and more than likely hire someone else), but I'm wondering if I can use my grinder to smooth it out, and put another topping on it and try to screed it properly this time. I'm hoping to salvage this and not have to jack hammer this shower pan up.
Yeah, a stone grinding wheel (a wheel for grinding stone) in you grinder will be able to sort out any uneven spots.
Be sure to wear a dust mask, silica dust is nasty stuff.
There's probably no need to screed unless there are still low spots, small low spots can be accomodated handled by using extra tile adhesive when laying the tiles.