"You shouldn’t need any to apply grout sealant – most grouting is water resistant nowadays, while also frost resistant and containing microban (to reduce bacteria growth). Just make sure to check that your grouting is waterproof/water resistant on the packaging.
Answered on 26th Feb 2019 - Member since Mar 2019 - report
Be sure to leave your grouting for 3 to 5 days (brand dependant – check the packaging), to be certain that it has set through correctly (reaching the joints, not just the surface layer between tiles).
You may want to consider sealant for corners of your shower, along the vertical line where, over time, cracks can appear. This will at least keep your tiles sealed, even if cracks do occur beneath.
The only time you would specifically need sealant is if the tiles were porous, where water could get through, but this is less likely if you are using bathroom tiles specifically."