The answer to 'grout grimy' is that grimy grout is a common problem caused by a buildup of dirt, grime, and mold. Symptoms include discolored, stained, or cracked grout lines. The best solution depends on the severity of the issue, but generally involves deep cleaning the grout using a specialized cleaner or tool, and potentially resealing the grout to prevent future buildup.
For minor grout issues, homeowners can often tackle the problem themselves with some elbow grease and the right cleaning products. However, for more extensive damage or mold growth, it's best to call in a professional cleaning service to ensure the job is done thoroughly and safely.