An exterior trim assembly for use with a window or door surround in a building structure comprises at least one mantle for affixing above the window or door, and first and second pilaster assemblies for affixing on the sides of the window or door. The mantle comprises a mantle base and a corresponding mantle cover to affix to and cover the mantle base. Each pilaster assembly comprises a base and a cover element affixed to the base wherein each of the bases has a plurality of regularly repeating reinforced structural sections. At least two pilaster cover plates are provided, each pilaster cover plate is affixed to and covering one of the first and second pilaster bases.