Tar felt has detached from wall and fallen away. How to fix?

[kez1]

Photo shows whats happened.
Tar felt is still intact and not cracked.
I haven't a big flame thrower to heat it all up and put it back.
How can I fix this without getting it re-done?
Anything that gets it satifcfactorly repaired and watertight will do.

 

[Alastairreid]

You can try a tin of cold applied tar from a tin...paint it on the wall and the felt and let it go tacky.
The felt will need to be warm and pliable so do it on a warm day....no idea how long it will last but its as quick a fix as you get.