Cement grout vs epoxy grout
Standard cement-based grout is fine for most walls and floors, is easy to apply and easy to repair. It is porous, so it stains and needs occasional cleaning and sealing.
Epoxy grout is effectively non-porous and chemical resistant, which makes it a strong choice for shower floors and wet rooms. It costs more, sets fast and is far less forgiving to apply, so it should be fitted by someone who has used it before.
Where silicone belongs and grout does not
Every joint where two different planes meet - wall to floor, tile to bath, tile to tray, internal corners - must be silicone, not grout. Those joints move. Grout is rigid and will crack, and a cracked corner joint lets water straight into the build-up.
This single rule prevents a large share of the bathroom leaks we repair.
Choosing the right silicone
Use a sanitary-grade silicone containing a fungicide for all bathroom joints. Cheap general-purpose silicone blackens quickly and bonds poorly to acrylic baths.
For baths, fill the bath with water before sealing so the joint is sealed at its widest loaded position. Sealing an empty acrylic bath is a guaranteed split joint on the first bath night.
Realistic maintenance schedule
Inspect corner silicone once a year. Re-grout hairline cracks as they appear rather than waiting. Replace perished or blackened silicone rather than applying fresh silicone over it - new silicone will not bond to old, and you get a sealed-looking joint that leaks.