Hi!
I am the proud joint-owner of a large and rather old lead-covered valley between me and my (semi) next door neighbour.
It is well in excess of 50 years old and has been laid on a wood base which was covered with two layers of old bitumen roofing felt. Over time I suspect the felt has melted and fused to the lead, cracks in which have been repair with some (unidentifiable) sort of tape. There are newer cracks (probably due to thermal movement) of up to 600mm long by