I think a netting type trellis or wooden trellis up against the wall would work much better than the single strands of string you are using now. The concrete wall will get hot and a trellis system will help the plant to cover the area and shade the wall.  This will help promote faster growth of the jasmine. I love the idea of hiding the wall with fragrant jasmine. Just remember this old gardening adage: The first year the plants sleep, the second year they creep then the third year they leap. In about three years it will look great. Keep growing, Marianne Binetti