I am soon going to attempt to repair a south facing lead lined roof gulley. The mortar has all cracked and become detached from the lead and also from the tiles. I don't see how mortar can ever successfully seal to a lead sheet, particularly when the lead to subject strong sunshine and thus differential expansion. I propose to remove the existing mortar and stick a bird deterrent "Prickle Strip" onto the lead gulley, underneath where the mortar will go, and then apply mortar above it in the usual way. The idea is that the spikes on the "Prickle Strip" will ensure that the mortar does not become detached from the lead sheet over time. Do people think that this will work ?