Answer:
A mortar joint is available when the bricks of a wall are not laid on one, but on two, mortar strips. In this case, the mortar has to be applied to the outer edges of the support surfaces of the bricks. By using a mortar joint, restrictions in the ultimate limit state are to be expected, as more unfavorable stress diagrams occur in the wall.
Whether or not a mortar joint can be applied in a European country is governed by the respective National Annex. The German National Annex does not allow the use of mortar joints for masonry construction. Therefore, in Germany, bed joints must always be mortared over the entire surface.
