Grinding out mortar joints - done first?

Whern doing a roofing job, wouldn’t you start preparation on chimney counterflashing first (there are 2 large chimneys to be done), so that the pieces of mortar would not be everywhere when you install gutter apron, I&W, etc ? What is your typical sequence there ?

if i understand you correctly no. you have to get to that point of the roof before you do the chimney. start from the bottom and work your way up. do not rack laminates you will have to step them.

Hope i answered your question its a little vague but you start at a edge of the roof and away you go.

I cut the reglet in the chimney during tearoff. New shingles will get dust all over them if you wait.

Its better to do before the new shingles are on because of the dust, but you can do it after the fact but make sure you lay out drop cloths.

We lay tarps around the chimney when cutting in. Before or after it doesn’t matter one is just cleaner then the other.