I've always been curious about the grout sponge. I have read up on them each time I come around and I am scared to try them because I am afraid they will scratch. Some say they wont and some say they will. I would think they would as the dirt doesn't always have something to fall into the sponge while it is being dragged across the clear like with a sheepskin mitt.
I would like to see a grout sponge test one a perfectly polished black car to settle the score once and for all. Polish the car, get the car pretty dirty and then wash wth a sponge. Good pictures before and after.
I don't have a black car to do soon, I have a new detail I will use it on it and take some shots, lady called me and wants it detail cost now a factor. Check web site Unlimited Auto Detail - Home