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.
Tywyn
Tywyn, previously spelled Towyn, is a town, area, as well as seaside resort on the Cardigan Bay coastline of southern Gwynedd, Wales. It was previously in the historic region of Merionethshire. It is renowned as the area of the Cadfan Stone, a rock cross with the earliest well-known example of composed Welsh, as well as the residence of the Talyllyn Railway. At the time of the 2001 census, 40.5% of the population were recorded as Welsh speakers. By the 2011 census this had actually reduced to 37.5%. These fairly high figures (provided the town's population analysis) show the use of both Welsh and also English as the medium of instruction in Ysgol Penybryn, the town's primary school. An Estyn examination record in 2010 noted that about 11% of the kids at the college originated from homes where Welsh was the primary language.