When you've fixed all your tiles to the wall, you should leave them for the adhesive to dry. How long this takes depends on the adhesive you use, so it's best to check the manufacturer's instructions. Then you can finish off all the joints with grout (special hard filler). To finish off your tiling, you might also need to add a waterproof seal along the bottom of a splashback, and possibly mount some fixtures too.
You can buy grout in powder form to mix with water, or pre-mixed and ready to use. But whichever you choose, check you've got enough for the job first. And remember to use waterproof grout anywhere that the tiles will get splashed. You can also buy coloured grout to match or complement your tiles.
Press a small amount of grout onto the face of the tiles with a trowel. Then use a grout spreader to spread it. Make long, upward diagonal strokes and work it thoroughly into the joints between your tiles. Carry on until you've grouted all the joints - but try to do this as quickly as possible, as the grout will soon begin to harden.
As soon as you finish putting the grout on, you'll need to go over the tiles with a damp sponge to remove any excess. Remember, it'll be very difficult to shift if it goes hard. Also, take care not to drag any grout from the joints.
After leaving the grout to harden slightly, use a grout shaper to finish off the joints and make them neat and tidy. Pull the shaper along the joints in one continuous movement. If any gaps appear in the joints, press in some more grout with the tip of your finger. Sponge off any excess.
As the grout dries, a powdery film will appear on the tiles. Simply polish this off with a soft, clean cloth to leave your tiles sparkling.
Moisture from baths and showers or food spills in kitchens can stain grout and leave it looking shabby, even when the tiles themselves are fine. You can remove minor stains and fungal growths with grout cleaner. This contains detergents and biological agents that clean the grout and get rid of mould. But if your grout is particularly dingy, you might need to scrape it out and replace it.
Use a grout rake to remove the old grout to at least half the thickness of the tiles - taking care not to scratch the edges. Do all the vertical joints first and then the horizontal ones, to make sure that you don't miss any.
Replace it with new grout.
Although waterproof varieties of grout do exist, it's best to protect the joint between a basin, bath or a splashback with a flexible silicone sealant. This will help with any movement in the fitting, which could cause the grout to crack and let water through.
To be sure you get a waterproof seal around your bath, fill it with water, then apply silicone sealant and leave it for 24 hours before emptying. That way, you'll allow for any movement caused by the weight of the full bath.
Put on a continuous bead of sealant, working from one end of the splashback to the other. Try to keep a steady pressure and speed when you're doing this.
You can smooth any irregularities in the shape of the bead with a special sealant shaper (or even a soapy wet finger), but take care not to pull the sealant from the surface.