Mortar is a mixture of sand, cement, and water that is used to fill in spaces between the bricks or stones in a buildings structure. Mortar can also be used as a sealant to seal the gaps between stones, bricks, or even concrete. Mortar is typically used as an adhesive for bricks and stones, and to hold them together. It is typically a mixture of sand, cement, and water. Mortar can also be used as a sealant to seal the gaps between stones, bricks, or even concrete.