The answer to 'grout buildup' is that it is a common issue caused by a buildup of dirt, grime, and mineral deposits in the porous grout between tiles. Symptoms include discolored, cracked, or crumbling grout that can make the entire tiled surface look dirty and old. The good news is that grout buildup can often be addressed with some DIY cleaning, but in some cases, it may require professional grout cleaning or even grout replacement.
For minor grout buildup, you can try scrubbing the grout with a stiff-bristled brush and a mixture of warm water and mild detergent. For tougher stains, you may need to use a grout cleaner or a solution of vinegar and water. If the grout is severely damaged, you may need to regrout the entire area, which is typically a job best left to a professional tile and grout cleaning service.