I know they grab onto wood and trellis' but, do they need some kind of support to cover a cement wall?
They wll grow with little support. I have seen them climb the side of a stucco house
they mostly will but ask your self one question. Are you willing and able to pay for the damage that will occur when you decide that you no longer want that vine on on your wall? When you start to pull the vine down it will bring chunks of concrete with it where the roots have grown into the wall, is it worth it?
Those vines will grow if theirs any little cracks in the wall. But their very invasive plants, and will eventually cover, the wall completely. At least mine of a similar variety did. Even broke down the wall some over a few years.
It depends how intact the cement is. If it has little crevices (from being old and disintegrating) the vine might grow, but otherwise, it'd need a trellis or other support on new cement. I DO know that old, unpainted clapboards on a neglected house will make a trumpet vine go NUTS, like the one on a house I once rented, whose landlord was too drunk to do anything like painting, for over 20 years! But the rent was cheap and I enjoyed the many hummingbirds in summer.
