window keystone

A window keystone is a usually wedge-shaped polyurethane decorative element placed at the centre of a window arch or the top of a surround. In classical architecture it is applied above the window as an ornamental element that emphasises the centre of the arch and completes the surround line. The polyurethane material is lightweight and is fixed directly with mounting adhesive; it resists moisture and impact, does not crack, blister or peel, and can be painted. Being very light compared with real stone, it is easy to install at high points on the facade and is not eroded by rain. Because it is mould-cast, the stone profile is identical on every piece. Polure produces window keystones in a range of sizes and models.