Hello,
My floor tile grout has gotten pretty gross and I've tried so many different ways of cleaning. In hindsight, I wish we would have sealed the grout. Also, there are some areas where the grout is gone.

Can I regrout over the old grout and avoid having to remove all of the old grout? Does anyone know?

if I have to remove the old grout, does it take a long time with the tool they sell in Home Depot?

Thanks.