 or you want to take it all up and do a properly tamped base here and then relay it down. In terms of the space between the patio, between the pavers, I imagine these are fairly wide gaps. Usually with flagstone, they're like a half inch or three-quarters of an inch or an inch or even more. And the problem is that if you put mortar in between that, it's just going to crack into a bunch of little pieces. I think what I would use is crushed gravel.