I had the same problem
I've Use Polymetric Sand it will get hard and no longer will be
removed when if rain
http://www.techniseal.com/products.p...=1&langue_Id=1

Remove the sand you have, replace with the polymetric sand like the
one from Techni-Seal, put in the crack 1/2 fill then spay water on in
let it dry for 4 hour then put another
this is specialy for Paver

hope it help