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.
Builth Wells
Builth Wells is a market town and area in the area of Powys and also historical county of Brecknockshire (Breconshire), mid Wales, lying at the convergence of rivers Wye and Irfon, in the Welsh (or top) part of the Wye Valley. It has a population of 2,568. A number of the town's buildings, including the 1876 Market Hall, were built from rock from Llanelwedd Quarry. Much of the dealing with and other dressed rock utilized in the building and construction of the Elan Valley dams was additionally quarried below. The quarry produced the first occurrence of laumontite in Wales. The quarry is currently run by Hanson Aggregates. Builth is a longstanding anglicization of the Old Welsh Buellt/Buallt which integrates bu be, similar to some Middle English orthography), indicating "ox" with gellt (later gwellt), indicating "lea or leas"; the same form is made use of regardless of gender of the animal. The town added "Wells" in the 19th century when its springs were promoted as a site visitor destination. Its modern Welsh name Llanfair-ym-Muallt implies "Saint Mary in Ox Leas".