An abutment is provided for use as a start or end post of a plasterboard partition wall or as a join between two such walls which run in different directions. The abutment comprises an elongate plaster moulding designed to run between the ceiling and the floor and having an abutment surface for abutment against the end of the partition wall. In a preferred embodiment, the abutment includes a tapered edge at the abutment surface to provide a space at the join in which a skim of plaster can be applied to provide a seamless join between the partition wall and the abutment.