Q: Are there any code required tolerance provisions for brick veneer walls? Would the construction tolerance requirements under ACI 530.1-05/ASCE 6-05/TMS 602-05 (2005 MSJC Specification) apply?
A: For most buildings, the short answer to these questions is “No.” Section 3.3.G.1 of the MSJC specification lists the site tolerances for the cross section or elevation; mortar joint thicknesses, which include bed joints, head joints, and collar joints; grout space or cavity width; variations from a line, from level, and from plumb; and location of the elements in the plan or elevation.
However, the commentary for Section 3.3 states: “Tolerances are established to limit eccentricity of applied load and load carrying capacity of the masonry construction. Since masonry is usually used as an exposed material, it is subjected to tighter dimensional tolerances than those for structural frames. The tolerances given are based on structural performance, not aesthetics.”
Therefore, although the MSJC specification does not specifically state that the tolerances do not apply to masonry veneers, the commentary suggests that the tolerances of exposed masonry, such as masonry veneers, could be tighter than those listed in the MSJC specification. Consequently, many architects establish tolerances within their specifications.
The 2003 International Building Code (IBC) does not require tolerances for masonry veneers. Chapter 14 - Exterior Walls in Section 1405.5.1 - Tolerances states: “Anchored masonry veneers in accordance with Chapter 14 are not required to meet the tolerances in Article 3.3 G1 of ACI 530.1/ASCE 6/TMS 602.” This information is restated in Chapter 21 of the IBC in Section 2104.1.1-Tolerances, where masonry veneers are again excluded from meeting any tolerance requirements.
The 2003 International Residential Code (IRC), in Section R607.2.1 - Mortar Joint Thickness Tolerance, actually provides tolerances that are more restrictive than those in the 2005 MSJC document. However, as with the other codes, this section also goes on to exclude masonry veneers from these tolerances.
Although the MSJC specification suggests that tighter tolerances may be required for aesthetics, and many architects include tighter requirements in their specifications, there are many cases where achieving tighter tolerances than those listed in the MSJC specification may not be possible. Depending on the brick selected for a particular project, tighter tolerances may actually exceed the allowable size variations of the brick themselves.
It is also important to note that tighter tolerances do not necessarily translate into better walls. There are many architectural veneers — in order to achieve different aesthetic effects — that intentionally vary joint widths more than these tolerances.
Q: How is flashing sealed where reinforcing extends through it?
A: Flashing is used in reinforced masonry walls that are not grouted solid. Water that penetrates the exterior surface can flow within the cells that are not grouted. Flashing is needed at the base of these cells to direct this water back to the exterior.
The flashing must be sealed watertight to be effective. With conventional versions, water can flow laterally on the surface of the flashing. If the flashing is stopped short of the reinforced cells, water can bypass the flashing at this point and flow into the area beneath it.
The flashing must be sealed at the grouted cell to prevent leakage in these locations. In a typical reinforced masonry wall with grouted cells, a hole is cut in the flashing where the reinforcing bar extends through. The hole is smaller than the cell so that the edge of the flashing projects into the cell. When the cell is filled and vibrated, the edge of the flashing is embedded in the grout.
Filling head joints
Q: I have heard that it is important to fill head joints with mortar. The Brick Industry Association (BIA) in its Technical Notes 7B includes a drawing showing mortar being placed on all four edges of the brick. I don't believe I have ever seen a mason do it this way.
Is this necessary? For structural reasons? To reduce water penetration?
A: Filling head joints is desired to resist water penetration. Head joints do not significantly contribute to the strength of the wall. In running bond, the strength of the wall to span horizontally is based on the brick units above and below the head joint and not the flexural strength of the head joint itself. In stack bond walls, reinforcing is provided because the bond of mortar in head joints is not relied on.
Partially filled head joints have less resistance to water penetration. Once water penetrates the outer portion of the joint, it can easily pass through the thickness of the wall. For this reason, care should be exercised to fill head joints.
BIA Technical Notes 7B states: “The best head joints are formed by completely buttering the ends of the brick with mortar and shoving the brick into place against previously laid brick.” Although Fig. 6 in this document shows a head joint where mortar appears to have been applied on all four edges, I believe that the point of this drawing is to show complete filling of the joint and not necessarily the method of placing mortar in the joint.
Most masons do not apply mortar to all four edges. The important point is that sufficient mortar is installed to fill the head joint. This scenario can often be confirmed by observing mortar squeezing out the top, back, and front when the units are placed. Another test is to remove random brick units immediately after they are placed to make sure that there are no voids and to confirm that the procedure is adequately filling these joints.