Question:Can I reapply a thin layer of grout over existing grout to look like new?Answer:Yes but you need to make sure you scuff the grout lines real well with a stiff brush. Lay the new grout on thick to allow for a build up, then wipe up gently, enough to get the excess off the tile but not to wipe off the new layer of grout. If that doesn't work to your satisfaction as sometimes it doesn't Google "Tile Grout Paint" and check out your options there.