I bought my house 3 years ago with the pool and spa already built, and the house was only 7 years old at time of purchase, so the pool is not that old. The previous owner choose flag stone coping for the top layer over the tile upper edge. Well, two pieces have not only come loose, but fell into the pool when our dog walked over them. Can I replace them myself by cleaning the area and using thinset and then grout after a couple of days?