Mortar

A paste of slaked lime, sand and water used to bind stone and rubble in walls. After the Norman Conquest, enormous quantities were needed for castles, cathedrals, monasteries and parish churches. It was usually mixed on site in pits or troughs. Lime mortar sets slowly and stays slightly flexible, which suited thick masonry walls. Stone halls and manor houses used it, while most ordinary houses were timber-built.

Sources: historicengland.org.uk