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The primary sign your grout has gone bad is clumping or a lumpy appearance during a project. If you notice this and can’t remember the original purchase date, it’s best to head back to the hardware store. If you use expired grout, you risk having it deteriorate as it dries and your tile falling apart weeks or months later.

If applied properly and with non-expired materials, grout shouldn’t “go bad” after application. Grout does have an average lifespan of about 15 years, after which you may need resealing, repairs, or replacements.

It is possible to put a layer of new grout over the existing grout, but removing the old grout is always better before regrouting. Otherwise, the new layer can be flimsy and may not attach properly to the old layer, eventually flaking off and leaving visible patches of the old grout. If you're nervous about removal, hire a professional.

No, do not seal the grout in your shower. Because the product is porous, it absorbs liquids. Sealer soaks in and makes the grout waterproof, but this means it can't "breathe," meaning the water that seeps behind the tile won't evaporate. Instead, install a waterproof membrane behind the shower tile. If you have natural stone, seal it before grouting. Ceramics and porcelain don't require sealing.

A waterproof membrane in a tile shower, also known as sheet membrane, is a barrier of plastic compounds between the bonding and cement backer board behind the tile. You can purchase waterproof membrane in the form of adhesive plastic sheets or a paint-on liquid that dries to form a barrier. The waterproof membrane creates a seal beneath the tile that prevents moisture from reaching the underlying surface.

Two coats of grout sealer are needed for most tiled walls and floors, but you don’t need a grout sealer for all projects. First, smooth a thin layer with an applicator or toothbrush. Wipe off any residue, and let it dry for at least 24 hours. Apply a second coat, remove the excess, and allow it to dry for another 24 hours.

The best tool for removing grout is an oscillating multi-tool (with a grout removal attachment). You can also use a reciprocating saw. Power tools will make the majority of the work go faster. When doing detailed work, use a manual grout saw or removal tool to get into difficult-to-reach or small areas. Wear protective equipment like safety glasses, and have a vacuum on hand for cleaning up the dust.