The Emergence of Thin Brick: Understanding adhered veneer

Within TMS 402’s section on adhered veneers, there are some general design requirements for all types of brick veneers, including water-resistant membranes, flashing, weeps, and movement joints. While there is no cavity to collect water like a cavity wall, flashing and weeps are still necessary at points of support. When using proprietary thin-brick panel systems, an alternative design procedure is often employed. The alternative procedures look at load distribution and adhesion. Performance requirements include a structural analysis usually performed by the manufacturer that has had its system tested and approved.

Typically, though, prescriptive design procedures are used. If done according to these requirements, they provide the same level of safety as the alternative design procedures. The limitations on the size and weight of the unit include:

• 
not more than 67 mm (2 5/8 in.) thick;
• 
not more than 914 mm (36 in.) in any direction and be no more than 0.5 m² (5 sf) in face area;
• 
not more than 718 Pa (15 psf) in weight.

This keeps the unit size and thickness down, ensuring they bond properly to the backing. Having shear strength not exceed 345 kPa (50 psi) shows the unit can stay bonded in place. Other prescriptive requirements include the backing containing a continuous moisture-resistant surface (e.g. building felt or other moisture barrier). Finally, while there is no limit on area of the brick panel, movement of the brick (expansion) and its backing (expansion or shrinkage) must be taken into account.

One additional requirement for adhered veneers 
is found in the International Building Code (IBC). In this case, an adhered veneer cannot weigh any more than 958 Pa (20 psf), which would equate to a 51-mm (2-in.) thick brick unit. On interiors, the floor supporting the thin-brick assembly must be designed so the floor deflection is no more than the span or ‘L’ of the joist or beam divided by 600. Keeping the wall from overloading the floor, this requirement mostly relates to wood flooring, rather than concrete.

Backing systems for thin brick
The backing systems appropriate for thin-brick veneer are wood, steel studs, concrete, or concrete masonry units (CMUs). As with other wall systems, some of these materials provide a more durable backing than others.

Wood or steel studs are an appropriate backing
for thin brick, but certain recommendations must 
be met since these are more flexible backings. 
To keep deflection and bowing to a minimum, it is recommended studs be designed for a maximum deflection of L/360. This may be rather stiff for a wood stud backing and may conform to the typical design requirements for a steel stud.

Regular drywall is not an appropriate backing. The sheathing over wood or steel studs should be:

• 
fiber-cement;
• 
fiber-mat-reinforced cement;
• 
glass-mat gypsum; or
• 
fiber-reinforced gypsum.

It is also important to note the waviness in the backing wall reflects in the thin-brick exterior. A typical thin-brick veneer with a steel stud backing is shown in Figure 2. The durability and moisture resistance of the sheathing and water-resistive barrier (WRB) dictate the system’s longevity. Better materials typically result in longer life. In some cases, a drainage mesh or mat is used to create a drainage space within the wall system to redirect any water penetration.

Concrete or concrete block are a very traditional backing for thin brick. The stiffness of the backing is similar to the stiffness of the thin brick so the materials are very compatible. As with most backings, there may be some surface preparation necessary before the thin brick is applied. Thin brick can be applied to a precast concrete panel, tilt-up wall, or insulating concrete form (ICF) walls.

Modular panels are very popular since they guide the installation. These include galvanized metal sheets with tabs; plastic panels with formed grooves; and metal rail systems. Panels are produced in various sizes, but they are most commonly 1.2 x 2.4 m (4 x 8 ft).