You should pull up and remove weeds by hand as and when they appear. If it is a regular problem, you might need to reseal the paving. In extreme cases, the sub layer itself may need to be re-laid. You can use weed killer, however some paving can be discoloured by stronger weed killers.
Calstock
Calstock is a civil parish and a large town in south east Cornwall, England, UK, on the boundary with Devon. The village is located on the River Tamar 6 miles (9.7 km) southern west of Tavistock and 10 miles (16 km) north of Plymouth. The church had a population of 6,095 in the 2001 census. This had actually increased to 6,431 at the 2011 census. The parish incorporates 5,760 acres (23.3 km2) of land, 70 acres (0.28 km2) of water, and 44 acres (0.18 km2) of the tidal Tamar. Ashburton Hotel and Danescombe Quay neglecting the River Tamar As well as Calstock, various other settlements in the church consist of Albaston, Chilsworthy, Gunnislake, Harrowbarrow, Latchley, Metherell, Coxpark, Dimson, Drakewalls, Norris Green, Rising Sun and St Ann's Chapel. Calstock town is within the Tamar Valley AONB, is forgotten by Cotehele residence and also yards, and pushes the scenic Tamar Valley railway. Calstock train station opened up on 2 March 1908. The village is twinned with Saint-Thuriau in Brittany, France.