curled lead chimney flashing


Does anyone have an idea why this happens? We had a new asphalt shingle roof put on about 5 years ago. The chimney lead flashing was replaced with new, and when all done, it was lying flat on the shingles as it should be.
About 4 months ago I noticed that one of the corners of the lead had curled up enough that wind-driven water might have been able to get into the house, so I went up on a step ladder and reached up with a very long snow roof rake to squash it back down flat. Worked easily. Now, i see that it is slightly curled up again, lifted perhaps an inch at this point.
Does anyone know what the mechanism is that is causing the lead flashing to curl up on that one corner?
Thanks.
emichael
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Could be that one side of the lead sheet is reacting to the environment and some of the Pb is being converted to an oxide or a sulphate or some other compound.

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Would that make it curl? And just one corner? I just have no idea if that would be the cause.
I wondered if maybe I'd imagined this, so went outside and checked again, and there is no doubt that it is curling again after being nicely flattened just those few months ago.
Thank you for your thoughts on this.
i wonder if there might be a mason in the group who has seen this?
emichael
John Gilmer wrote:

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I don't know. I was just throwing out an idea.
It's quite possible that a lot of lead today is "re-cycled" and the folks who produced the sheet lead might have been sloppy. Pure lead is quite soft and IF you curled it up it would "relax" on its own.

You might get a propane tourch or a soldering gun or iron and some tin/lead solder. The solder melts as a lower temperature than pure lead and you break off a corner, flip it over, and solder it back into place.

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hah, interesting idea!
John Gilmer wrote:

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