What is a thin, coarse mortar, used for pouring into the joints of masonry and brickwork; also, a finer material, used in finishing the best ceilings. Gwilt called?

grout — A thin, coarse mortar, used for pouring into the joints of masonry and brickwork; also, a finer material, used in finishing the best ceilings. Gwilt. (Webster's 1913.)

Sources