Hydrochloric acid. It's the very best, and you only need a cup full. Not now sold to the great unwashed, but just get a tradesman to get you some.
Hardware stores stock the gentler version, called Spirit of Salts, but you might need two bottles (about £3.00 each when a bought it a few months ago).
Both are very nasty to use, stink to high heaven, but get the job done once and for all.
Good Morning Wednesday 20th May 2026
Can we get rid of the nasty adverts?
