My wife and I moved into our house a little over a year ago and need to make a few minor repairs, including the floor in the 2nd bathroom. The grout between the tiles seems to me crumbling and I'm not sure what to do about it. I'm looking for an easy and/or quick fix. I'm not really concerned about the grout matching, since I'm sure we will renovate the bathroom in the not too distant future. I'm attaching some pictures to help explain what I mean. Thank you for your help.