The castle was primarily built from bricks, with stone used for the detailing, such as doorways. The brickwork was decorated with patterns of darker bricks, called diapering, which was used to show symbols associated with Lord Hastings, as well as objects such as a jug and a ship. This style of decorative brickwork and stonework was popular across England at this time, but particularly so at Eton College, where John Cowper, the master mason on the project, had been an apprentice. Although the castle was not extensively decorated, the brickwork at Kirby Muxloe was skillfully executed, with the bricklayers cutting and shaping the kiln-fired bricks to produce spiral and domed vaulting.