hi Pattimac, in the street of the big DIY, but then on the opposite side of the road, a bit closer/direction to the Tuesday market, there is a shop that sells grass seeds, lawnmowers, etc. They have the right stuff to kill weeds in pavements or garden paths. It is a liquid, that needs to be mixed with water and sprayed on the areas where you need to get rid of weeds. The owner can give you good advice (as he gave to us)
Good luck!