Is it strong enough? Do you need reinforcement of the mortar? What sort of material are you going to use to cover the mortar or is the mortar a finish?
Before installing the mortar make sure the wall is clean and free of debris. You may need to pressure wash the wall before installing the mortar. Following the mixing instructions of the mortar carefully. Apply the mortar evenly with a trowel. Try not to get mortar on your hands, or use gloves, as it tends to dry out your skin.
Stucco. Pressure wash the brick and scrub all mold and mildew off. Use lots of bleach. Then buy some masonry mortar or stucco mix and apply a scratch coat (rough coat) on the brick. Then after it dries you can add a second or third layer with a finish of your choosing.