I am looking for some advice on the best way to remove some 40 year old mortar from my back porch. It was part of a brick wall that was removed a long time ago. I have tried a metal scraper and a wire wheel drill attachment but neither really worked. I was thinking about purchasing an angle grinder (with masonry wheel) or an oscillating multi tool to help me get this finished. Which of those (or something else) do you think would work best? (photo attached)
Hard to say from that picture.
For the big chunks a brick chisle should get most of it off. If you want it to look better rent a concrete grinder.
A 4-1/2 grinder will get it off but will never leave it flat and smooth.