Posted by DMB on 27/07/2022 20:23:55:
Bryan,
Thanks for that, what do you suggest?
John
The best thing I've found is intumescent sealant, as used at work for firestopping cable holes.
Cleans off with water, floats to a reasonable finish, and stays flexible. It seems to stick to anything slightly porous, if you dampen the surface first.
Bill