In article .com,
"frank spencer" writes:
How can I remove waterproof tile cement from the face of ceramic tiles?

A thin layer will usually brush off or come off with a plastic
pan scourer, because it dries out before the cement sets.

Failing that, try something acidic to attack the cement (and
hope the waterproofer doesn't completely stop it getting in).
Brick Acid is sold for the purpose, but I have successfully
used kettle descaler for this. Be careful with any metal
tools, as the metal can easily mark glazed tile faces, but
a combination of acid followed by brute force can break the
bond.

--
Andrew Gabriel