If your bathroom is tiled, or if there is a tiled splashback around the bath, the simplest solution is to bridge the gap with quadrant tiles the ceramic equivalent of wooden quadrant beading.
These are normally available singly as straight lengths with both ends cut square, or with one end finished in a bullnose, and in mitred pairs for coping with internal corners. One drawback with quadrant tiles is that they are becoming difficult to obtain, and it’s worth bearing in mind that not only can they work out quite expensive, but they also come in limited range of colors (designed to existing bathroom suites rather than tile ranges).
If you’re going to seal the gap in course of actually tiling the wall splashback, then you can fix the tiles in position and grout them in the way, 12-24 hours after the last has been pressed into place. In to accommodate any movement, you should make sure that the Wes bedded in a thick layer of silicone where they rest on the bath’s lip. On the other hand, if you’re faced with existing round the edge simply bed the tiles in mastic from start to finish. using instead of grout as well.
Quadrant tiles can be used successfully in situations where the wall is not hied—pew painted, papered, or timber-ciad.
However, in the last case it’s worth considering the use of timber quadrant beading as an alternative. All you have to do is pin it to the cladding or fix it to clean, bare plaster using an epoxy resin adhesive.
Again, make sure that the timber is bedded in mastic where it rests on the lip of the bath, shower tray or basin. Do remember to treat the timber with a good-quality preservative (one that can be painted or varnished over) and then paint or varnish it all round, including any cut ends, before fixing it in place.