if you like me are fed up with weed killers being diluted by the rain and your paving still grouted with 'green', a quick fix that my mother used is worth using. After making a cuppa, use up any very hot water left in the kettle on the dreaded weeds. It works very quickly and well. A few weeks back I heard this method mentioned on Gardeners' Question Time, I think by Bob Flowerdew. In the picture the green in the cracks is Helexine which I love and spare the hot water.