Column casings are formed by face fixing your chosen flat cladding panel/board close to its outer edge (using mechanical screw fixings) into a suitably prapared packer or the structural element behind. A suitably sized corner protector/angle is then bonded into position to cover the face fixings and to provide functional impact protection and/or a decorative finish.
A range of proprietary and bespoke corner protectors/angle can be provided made from materials including plastic, aluminium & stailess steel. The drawing below shows a typical detail for this method of construction.