Loose grout or sealant usually causes cracks around the bathtub, shower or bathroom tile joints. If these cracks are not quickly cleaned out and filled, they can let in water that can damage your walls and the framing behind them. This provides a perfect environment for mould growth inside your walls. Cracks grow mould. Mould is increasingly recognized as contributing to health and indoor air quality problems.
Cracks should be cleaned thoroughly before installing new grout. New grout should be installed in the joints between tiles. Since tubs expand and contract slightly due to temperature differences, grout is not suitable between the tub and the tile walls. Silicone sealant is required in that location.