I've put a new patio in and instead of using a wooden pergola I would like to make one with cast 'concrete colums'. This is a small scale DIY operation so I only have basic tools. My plan so far: concrete footings with re-bar ( to form support for column). Use a plastic soil pipe as mould. I'm not sure if I need some sort of grease/oil in mould? Sould I cast it in one piece or a section at a time? What ratio of sharp sand/cement should I use? How long should I leave the mould on? Does it matter that I don't have anyting to vibrate the concrete to get rid of air bubbles. Or should I just experiment?