The message
from Steve Walker contains these words:



My parents' garage spent a number of years with a crack that had been
patched with car body underseal - the really thick stuff almost like tar.
Lasted easily until they were ready to re-roof it.

I've used that and various other bituminous products on several
occasions. With a bit of scrim pressed into it, it makes a very solid
repair. Some of the repairs I did that way almost 40 years ago are
still holding good -- does that count as "semi-permanent?" :-)