1. Grout

Option No. 1. Grout

If the gap can reach only a couple of millimeters (no more than 5), then for its location you can use grout. Get a white grout or use the seams between the tiles. The superiority of this option is the resistance of grouting to penetration of humidity and saving color for a long period of time. It is possible to strengthen this effect of grouting by processing it with a means of protection against rust and mud (Fuga-shuscum). Ground is applied with a rubber spatula.