Grout to attach metal chimney to the masonry chimney?

[plan-g]

We have a (masonry) chimney up to about 1m above the roof. Down in it is a roughly 1.5m high metal chimney wedged and sealed.

During strong winds last fall, the sealant between the metal chimney and the masonry chimney came loose, and the metal part started to wobble.

I will now once again wedge and seal the metal chimney in the masonry chimney.

What type of sealant should I use to attach the metal chimney to the masonry chimney?
It should both keep everything in place and protect against moisture. Should it be elastic or rock-hard? I have something at home in a tube called gummiasfalt. Could that work?

 

[plan-g]

So it's this one that should be wedged down and fixed into a masonry chimney.