I am writing this blog not only because my own lower-face mesh mask came unglued after I left it in my car during a hot summer day in the high desert of Southern California, but because I know several other people who have also had similar issues with their masks. Not to sound like a cheap-skate, but I can't say I was too interested in shelling out another $20 bucks for a new mask, so I decided to see about just fixing the one I had.  I was very glad about my decision in the end.
Lower-face mesh mask
Photo by Tom Harris for the Pyramyd Airsoft Blog
*I added an asterisk in the title of this post because if you don't have the correct tool(s) already for this procedure, then it would not technically be free for you.  This is assuming you already have something that would work.