Chimney flashing lead and white stain?

Just need to know why after chimney counter install, is there a white streak coming down on the roof. I grinded out and am in three quarters of an inch. What is on the lead that causes it? Or is it the chimney?and it is also sealed with geocell. Will replace shingles. Just a hassle that maybee I can avoid in the future. Have done alot these and this has happened a handfull of time Thanks for any help guys.

concrete dust got wet and streaked maybe.

gweedo

Ditto, Mortar Dust will do that…

Lime from the mortar causes those stains.

A masonry Acid Wash on hard surfaces will work, but will degrade the asphalt in shingles if not watered down and washed off quickly.

Ed

cut your groove during tear off and new shingles will never see dust

I wouldn’t think it would streak down unless it was leaking.

Taken off many lead flashings around iron pipe that were corroded with white powder.

Good advice.

Also stick the nozzle of your blower
inside the grooves of your cut.

Also if your flashing is not copper than you should paint them the color that would match your roofing.

Lead doesn’t have to be painted to last
but i think it looks a whole lot nicer and will stop the streaking.

its also a good idea to put down a drop cloth when they cut a reglet.

Thanks guys