Assembly of segmented seals can be problematic in areas of limited space for an introductory tapered mandrel and where there are the problems with damage to the seal surfaces 23, 24. By the present method and arrangement, a seal formed from segments 22 is expanded to an expanded state and then retained at that state by the use of a sacrificial material 26 in the gaps 25 between the segments 22 opened by expansion. The sacrificial material 26 is typically a low melting temperature wax and so is removed when the seal arrangement reaches its operating temperature.