Standard wall and floor grout is not suitable for grouting worktops. Only an epoxy grout, such as Larsen's Epoxy Grout, should be used for grouting worktops.
This is because normal wall and floor grout is water resistant, which means water and other liquids can penetrate the surface of the grout and not affect the grout. This is not ideal for where food preparation is taking place. Epoxy grout is impervious so nothing can be absorbed into the surface of the grout. Larsen's Epoxy Grout is suitable for swimming pools and commercial kitchens.