I did a small tile and grout job today. I noticed that the dining area which I think is lightly used looked near perfect as well as the garage entrance and utility room. Those all came out great, but weren't real bad to begin with. The kitchen however was a totally different story. This was all ceramic tile in all areas. I applied Grout master and gave it plenty of dwell time and scrubbed all the grout lines with a grout brush followed by an SX-12. Nothing seemed to budge much in the kitchen for some reason. I could tell there were dirty areas, but they just weren't coming out. I find out after the job is over that the customer has applied grout sealer every year for the last 15 years to this grout! It was not professionally cleaned even one time in all those years to the best of my knowledge. My guess is she not only sealed the grout, but some of the dirt and stains along with it. This was only prevalent in the kitchen, other areas looked fine accept for some small imperfections right next to the baseboards that wouldn't budge. What pains me about this type of work is the customer expects the grout to be like new perfect when you're done. Now my question is this, can a build up of old sealer be removed by cleaning, period? Is it even possible? I suggested she have the grout color sealed as it appears to be the only reasonable fix. I have no desire to color seal, but if it were my kitchen and it even would make it look good another 5 years you can count me in all the way! I read on here a discussion about "acid wash" with Viper Renew. Why would you do that and will it remove old sealer? Can color seal be applied to the old sealer or will that cause it to just eventually flake off?