On Wed, 28 Oct 2020 17:02:30 +0000, Andy Burns wrote:

a lot of residue on the tile faces, now rock hard.

Residue as in a thin film or ridges of set grout? For the former just
use the shower and wipe down the tiles after every use it'll
eventually go. Even the ridges become slighly less attached after "a
while".

cover in kitchen roll and keep misting it with a plant sprayer for a day
or two?

Naw, not with a cement based waterproof grout. Spray with a mild
acid, citric or calgon or kettle descaler or WHY. Might be able to
make a paste with citric spread on scrape off hopefully with the
grout or just work it in/around with an old tooth brush. Any scraper
needs to soft and not metalic.

--
Cheers
Dave.