Hello Phil
We clean 1000's of bathrooms mainly commercial but the same principles apply to both.
Clean first with a mild alkali cleaner to get rid of body fats etc and follow up with a mild phosphoric acid based cleaner.Scrub the grout lines with a tooth brush or better still a commercial equivalent.Rub the tiles with a scotchbrite-clean again with alkali and rinse with plenty of water.The tiles should now be really smooth since the limescale should have been removed.
And this is the problem and why we got into colour sealing - the grout lines will probably be stained in areas and at best discoloured(yellow) - we found even with a steamer that this discolouring remained.
We would carry out the clean above and then just colour seal- the results are sensationsl and the grout will look brand new - better still the cleaning of it is now very staright forward so some real value for the customer.
It is a very staright forward process and saves hours of scrubbing to only end up with very mediocre results.
I have tried to add a couple of before and after photographs of a Hotel we were working in last week where they had applied the dreaded grout pen - this has to be scraped out -however most comes off with the deep clean described above.
Its the first time i have tried to put photos on so if they don't appear i will try again later or phone me (07831 249600) and i will send them to you.
Hope that helps and i haven't ambushed the post - it just happened to be something that we do all the time.
Steve