Regrouting Tiles

[kuulteach]

Is there any product that is waterproof . Bathroom shower is in need of a returb. Done this before with so called super products to no avail long term. And, same for my tile in hob backsplash. What I'm asking for is to be able to (r e g r o u t) tile with some degree of lifespan . Not
That I'm lazy . Just want effort to equate with longevity. Allowing.g for fact that my home is a 16th c cottage listed grade. 11 listed. So cant knock too much about

[SirOracle]

Did you remove the grout completely before regrouting kuulteach ?

[buildersmate]

You don't say what is happening to the tiles. Becoming loose presumably?
If so, this is dependent on the firmness of the substrate below the tiles. If it moves, it puts pressure on the grout.
There are additives that can be put into dry grout mixes (that are self-mixed with water). These improve both the flex and the waterproofing of the product. You get these from tiling retail specialists, probably not from DIY sheds.

[kuulteach]

Nothing wrong they just look mouldy in places so I want to regrout