On Oct 29, 6:00*pm, root wrote:
Breifly, the next-door neighbour has plastic, square guttering on their side
of the two semi's. We have the original round guttering which feeds a cast iron
outlet into the downpipe. The gutter leaks badly where the square and round
types meet.
It turns out that while the new guttering does actually have a square-round
adapter, this has merely been placed into the downpipe's outlet with no sealant
or physical attachment - it just flaps around in the wind and rain.

While up t' laddter today I decided to see what remedies were possible. The
round outlet has two screw-holes in its base. The side that goes to the half-
round guttering is screwed onto the outlet, the side that goes to the adapter
isn't - it's just loose. This appears to be because of a mismatch in the
"systems": modern outlets have a rubber seal to make a watertight joint, the
original cast iron outlet expects the guttering to be screw in and doesn't
have a gasket.
The plan is to bed the loose end of the adpater into some adhesive goop and
possibly to drill a hole up through the adapter to form a physical attachment
(as opposed to simply an emotional one). Though I'm a little dubious whether
a hole + metal screw would stand the test of time.

So, the question is: do I need to consider thermal expansion in the joint?
Would an adhesive ultimately fail due to movement, and/or should a screw-hole
in the bottom of the adapter be elongated to allow expansion along it's length?

Temporaryish repair can be made if you clean up,bitumous paint and
then flashband on the inside. Lasts a couple of years.