Many architects use recessed brick courses to create a reveal in masonry walls. I have heard that reveals increase water penetration into the masonry veneer.
Is this situation typically a problem?
Recessing a brick course to form a reveal in masonry veneer can increase water penetration in that portion of the wall. The reveal typically creates a ledge that can interrupt the flow of water down the face of the wall and increase penetration as a result.
Also, the top of the reveal is often difficult to keep watertight and is particularly difficult to tool. Even after tooling is done properly, there is often more cleaning performed in this area to remove any mortar smears on the top surface of the brick at the ledge. Aggressive cleaning of this area further increases the likelihood of water penetration.
When standard core brick units are used, the edge of the cores are closer to the exterior face of the mortar joint. The deeper the reveal, the more serious the concern. On deep reveals, any etching or weathering of the mortar in this vicinity can expose the brick core to rainwater.
The flat surface at the reveal also tends to collect snow and ice during winter months. This situation further exacerbates the potential deterioration problem.
For all of these reasons, reveals in masonry tend to increase water penetration into the wall and may increase the potential for deterioration. Reveals, however, often add a significant aesthetic impact to a wall and, therefore, do have a place in brick masonry.
The potential for water penetration is reduced by using solid brick units below reveals. Also, the units at the base of the reveal should have a chamfered edge. A 45-degree angle on the edge of a unit directly below the reveal quickly moves water away. This sloped surface reduces the impact of the ledge that might otherwise direct rainwater or collect snow and ice, which can lead to deterioration and water penetration.
I typically do not recommend using a mortar wash at the base of the reveal because the mortar deteriorates after a short time, falls from the building, and exposes the brick wythes to the impact of water penetration described above. Using sealant to make a wash can be more effective than mortar; however, this approach is still a maintenance item. Also, sealants collect dirt, which can create stains on the face of the wall.