I had porcelain tile installed on my back porch. I wanted dark grout but ended up with white grout (another story). I am going to use polyblend grout renew to darken it. First of all, does any one know if polyblend renew is a penetraing product? Also reading on the internet, I see alot of problems with water causing the color to fade. Overtime there will be snow, mud and water from the dog dish that I might not be able to clean up immediately. Could I use polyurethane over the grout or does the grout need to breathe? Thanks for any advice.