though. After you kill or remove the weeds,you need to replace these areas with polymeric sand. It helps prevent new weeds from growing. If you keep the maintenance up on your sand,you will keep the weeds out. You can usually get this sand at Lowes or Home Depot. You fill the cracks, then sweep the excess into the joins and make sure you try to get all of the excess off of the pavers while leaving sand in the joints. Spray a fine mist over the entire area. The polymeric sand will cling together and harden like grout.