A few months ago I realized that my nails were becoming brittle and weak, and they started breaking/chipping all the time. I started using Sally Hansen's Hard as Nails at least once a week, hoping to add some strength to my nails. Within the second week, I noticed that my nails were able to withstand more than before. I definitely recommend buying this if your nails are weak and chip very easily. I'm now able to grow my nails long without worrying about them breaking.
A few months ago, my nails would have never grown this long without chipping.
I recently bought a nail hardener by Nabi. I'm hoping it will work as well as Sally Hansen's.