Mortars are used in masonry for joining stones, bricks, blocks etc. and plasters are used for rendering on the outside and inside of walls. The differences between mortar and plaster lie in the capacity of plasters to take better finish, which depend to a very large extent on the type of sand used in the mix. For plasters we use finer sand. However the term mortar is also used loosely to refer to both plasters and mortar.