Using Thin Brick for Lean Construction

OCT_Thin.doc, 2398 words, 8 pics

Using Thin Brick for Lean Construction

Thin and full bricks face off

by Randy Wilson

In addition to being budget-conscious and schedule-driven, many building owners are concerned with environmental issues. Architects are expected to give owners designs that balance these criteria and provide structures that project the community image. Their relationship begins with dialogue to uncover the owner’s building philosophy and explore the natural balance of meeting expectations with construction realities.

If the final decision includes a masonry appearance, the architect should not automatically select a traditional full brick/cavity wall. A thin brick wall assembly offers many options and benefits to the owner, and can perform as well as, if not better than, a full brick/cavity wall solution.

Used for centuries, full brick is a 102-mm (4-in.) thick material. In the United States, many durable and impressive structures were constructed with load-bearing full brick walls (typically of two or three brick thicknesses that carry the loads of all floors).

In the early 1900s, long-span members such as steel and cast-in-place (CIP) concrete eliminated the need to use full brick as a load-bearing wall. During the 1940s, architects began to use full brick as a veneer—the only function the masonry units served was to give the appearance of a structural brick wall. Full brick veneer walls (practically the only brick wall used today) are made to look like load-bearing walls.

Brick’s appearance is in high demand—it has always typically conveyed wealth, security, and prestige. Thin brick is primarily used to project this image.

The material

The standard specification for typical thin veneer brick units is ASTM International C 1088-07a, Standard Specification for Thin Veneer Brick Units Made from Clay or Shale. Thespecification[by ‘it,’ do you mean the specification or thin bricks?] was created in the early 1950s by the Brick Industry Association (BIA), which perceived the need for thin brick units for renovation and re-veneering projects. The material’s physical properties and appearance characteristics are very similar to full brick as shown in Figure 1 (page XX).

ASTM C 216, Standard Specification for Facing Brick (Solid Masonry Units Made from Clay or Shale) and ASTM C 1088 share identical material characteristics because the two products are made from the same raw materials and manufacturing equipment. In most cases, thin brick has been traditionally produced by cutting the face off a full brick.

As demand for thin brick grew, alternative products offering better performance emerged in the marketplace. These materials exceed characteristics of ASTM C 1088 and ASTM C 216 as follows:

1. Dimensional tolerance for 203-mm (8-in.) material: +0 to –1.59 mm (–1/16 in.)

Tighter size tolerances reduce labor cost and allow material to be used with cast-in-concrete wall systems.

2. Distortion tolerances for 203-mm material: –1.59 mm.

The material is flat and true which saves labor and reduces breakage due to shipping.

3. Water absorption: Maximum six percent by five-hour boiling test. Materials yielding less than three-percent water absorption are considered vitreous. Brick’s porosity, permeability, and water absorption are important factors that influence resistance to freeze–thaw cycles.1

When using thin brick in concrete, these standards should be followed. ASTM C 1088 is adequate when adhering thin brick to the wall (not casting in concrete). This new, unclassified, thin brick material meets the above standards and is produced to finished size in a similar process as that used to manufacture traditional products such as acid brick and quarry tile. For the remainder of this article, ‘thin brick’ refers to this type of material.

Manufacturing

Thin brick is made with the same raw materials as full brick (i.e. shale, clay and additives) but is extruded and fired in much the same manner as ½ “ thick quarry tiles. Thin brick produced in this manner are denser, less expensive and use less raw material and energy than their full brick counterpart. Quarry tiles are known for their exceptional strength and durability. They are commonly used in the most demanding interior and exterior applications such as commercial kitchens and pedestrian walkways.

Most domestically produced quarry tiles are vitreous, having absorption of less than 3% and can withstand 3,000 freeze thaw cycles or more. In comparison, full brick often exhibits absorption rates of 17% or higher and are typically tested for only 50 freeze thaw cycles. Although thin and full brick are made of the same raw materials, a 16-mm (5/8-in.) thin brick used in conjunction with the proper wall assembly will out perform a 102 mm (4-in.) full brick used in a traditional cavity wall.

Traditional sawed veneer brick has been produced for more than 50 years as a full brick with one face cut off. (In rare cases, both faces are removed). The full brick’s core material—created after the brick unit’s face has been removed—requires additional manpower and energy to regrind, recycle, or reuse. In contrast, the more energy-efficient thin brick is produced as a split tile. The finished product yields less than 10-percent manufacturing waste material that requires regrinding.

The U.S. Green Building Council (USGBC) has granted a point under its Leadership in Energy and Environmental Design (LEED) program’s Innovation in Design (ID) category for the energy saved to manufacture and deliver thin brick. On average, thin brick requires 80 percent less raw material and natural gas than full brick (Figure 2, page XX). Delivery cost and diesel fuel savings routinely exceed 70 percent.

Figure 2 shows the energy savings obtained when thin brick is chosen instead of full brick. For every 2230 m2 (24,000 sf) of thin brick used in lieu of full brick, a designer saves 1456 L (385 gal) of diesel fuel, 290 tons of earth, and enough natural gas to heat a home for more than eight years. Thin brick wall assemblies can add to the energy savings, reduce the initial construction cost, and, in most cases, significantly lower the total cost of building ownership.

The wall assembly

A thin brick wall assembly can offer more options than traditional full brick cavity wall construction. Once the owner’s requirements are clearly defined, various attributes can be evaluated to determine the most suitable wall assembly for a project.

Direct-applied systems

The recommended installation method for a direct-applied system is outlined in the Tile Council of North America’s (TCNA’s) Handbook for Ceramic Tile Installation, TCNA W201-02 and W202-02. Also referred to as the ‘thick set method’ by the Brick Industry Association, it begins with a stable substrate of wood studs and sheathing, metal studs and sheathing, insulating concrete forms (ICFs) and concrete wallboard, concrete, or concrete masonry units (CMUs). The substrate is protected by a waterproofing membrane and/or one or two layers of #15 felt paper. A thick setting bed of cementitious mortar is applied to a layer of metal lath, forming the scratch coat. Once cured, a thin set mortar bed is installed to apply the thin brick. The mortar joints are tuck-pointed and cleaned to complete the process.

If the substrate is a concrete material (e.g. CMU, cement board, precast, tilt-up panels, or CIP) which has been sufficiently cleaned and/or sandblasted, the thin brick can be applied using the thin set method. This process is similar to the thick set method, except the scratch/metal lath step can be eliminated.

Pre-engineered thin brick assemblies are gaining popularity. These proprietary assemblies are made from sheet metal, polystyrene, asphalt-impregnated fiberboard, and other materials depending on the manufacturer. All assemblies consist of a pre-aligned grid, mortar-locking mechanism, and water drainage plane. Most carry a multi-year warranty and are engineered by the manufacturer for a project.

Direct-applied systems can be used in any application where an architect considers a full brick cavity wall. In addition to environmental benefits, thin brick’s advantages include:

 less weight for the structure to support;

 elimination of metal ledge angles;

 omission of foundation support for brick;

 reduction in the wall’s thickness, which increases floor area; and

 extra space in the wall to add more insulation, which reduces utility bills.

Cast-in-concrete systems

A popular use of thin brick has been casting the material in precast, tilt-up, or cast-in- place concrete. This procedure has its roots in Ancient Rome, where masonry components were cast into concrete structures including the Colosseum. In 1971, the first major modern structure (having a steel frame with precast skin) was constructed using brick-faced precast panels in Denver, Colorado. Since that time, thin brick cast into concrete has performed strongly.

The production process is simple. The contractor secures a form liner that comprises a brick grid system into the concrete form. Each thin brick is set into the grid to form the brick coursing. Concrete is poured into the forms. Once the concrete is cured, the concrete panels/components are removed from the form (in the case of cast-in-place concrete, the forms are removed). The components are cleaned to reveal a traditional, hand-laid brick appearance.

Although precast, tilt-up, and CIP assemblies each possess unique attributes, they contain similar market advantages in some regards. An architect should consider one or more of these options when the owner requires a quick schedule, a 100-year old wall system, a highly repetitive design, or minimization of total construction costs.

Brick-faced concrete systems are most popular where the structural component can also serve as the building’s architectural component. Designing exterior walls to serve as a load-bearing component can save project time, money, and materials; it can also improve the wall’s R-value when using an integrally cast insulation system.

Precast concrete components are cast in an offsite manufacturing facility. This single feature expedites the overall construction schedule and improves project quality assurance through the Precast/Prestressed Concrete Institute’s (PCI’s) quality control programs.2 Many precast plants can construct the entire building (i.e. structure and skin), whereas others are primarily architecturally focused.

Tilt-up concrete panels are formed, poured, and lifted in place on the construction site. The Tilt-Up Concrete Association (TCA) includes a personnel certification program to ensure every crew is staffed with quality craftspersons.3 These systems expedite a schedule, provide design freedom, and in most cases, save construction costs and offer long-term performance savings.

Recent technological developments have given the designer an opportunity to cast thin brick into cast-in-place concrete. This system is used in cases where the owner desires a masonry appearance, but only a CIP wall can meet performance expectations. Examples include shear walls, retaining walls, bridge abutments, and exposed foundation walls.

Costs

In most cases, pre-engineered thin brick assemblies are about $2 to $6 cheaper per square foot than full brick. However, if installing full brick as a wainscot along the base of a structure, full brick is cheaper. To skin a high-rise building, thin brick is less expensive—hoisting thin versus full brick to the top of a skyscraper is significantly easier.

In general, a tile plant can provide thin brick to the site cheaper than a brick plant can offer full brick. Thin brick manufactured using quarry tile production methods is less expensive than full brick. However, thin brick made by slicing off the face of full brick is a more costly process than that used to manufacture full brick itself.

Thin brick specification and selection

Thin brick should be specified in the wall system section—it does not have to be added in the masonry section as the material is not used in a cavity wall.

For example, in a precast parking garage project with thin brick cast into the precast components only (i.e. no other thin brick is on the site), the material shall be described in 034100–Precast Concrete Specification, Part 2–Products. Including a masonry specification to describe the thin brick would be redundant.

Through its Architectural Precast Concrete Committee, PCI has developed a standard for thin brick. With adaptations to meet the desired wall assembly, the standard forms the basis for all thin brick specifications. PCI’s recommendations include:

 size tolerances of +0 to –1.59 mm for material 203 mm or less;

 size tolerances of +0 to –2.38 mm (–3/32 in.) for material between 203 and 305 mm (8 and 12 in.);

 material thickness between 12.7 and 25.4 mm (0.5 and 1 in.);

 material of six-percent water absorption to ensure compatible thermal expansion and contraction with the concrete; and

 a dovetail or scored back to create a mechanical bond as opposed to one of mortar.

Full brick manufacturers who ‘saw the face’off anFBX-grade [please define](defined as a brick with a higher degree of precision and lower permissible variation) full brick to create a TBX (same standard) thin brick, claim to meet this standard.

Full brick is made for use in cavity wall construction, and performs based on a bond between the brick and Type-S mortar. The thin brick material described in this article is specifically produced to serve thin brick assemblies. The low water absorption reduces water penetration, diminishes material expansion, and allows the ‘brick in concrete’ assembly to endure 3000 freeze–thaw cycles. As mentioned, full brick walls must pass a 50 freeze–thaw cycle test—therefore, if the face is sliced off a full brick and used as a thin brick, it will begin to break down after 50 freeze–thaw cycles, because of its higher percentage of absorption.[What effect do freeze thaw cycles have on exterior thick set applications?]

In a field-applied system, the thin set and mortar should be a latex-modified material. These materials give the wall more pliability, have waterproofing additives, and enhance bonding due to thin brick’s low water absorption properties. Consulting a thin brick manufacturer can help define the best mortar for their material.

Conclusion

Full brick should be specified when a project can procure it cheaper than thin brick. These instances are rare, and typically involve one-story construction, plentiful labor and materials, and a more flexible schedule.

Thin brick assemblies give the architect design freedom not possible with full brick walls.

Full brick was designed to be an integral part of a structural wall. Since the development of the long-span member, brick’s role has been regulated to appearance and thermal mass. In the last three decades, thin brick wall assemblies have developed these characteristics and more, namely:

 construction speed;

 no maintenance;

 durability;

 low sound transmission (as concrete walls offer better acoustical performance than full brick walls with stud backups);

 construction cost reductions;

 marketplace availability;

 testing data;

 high R-values;

 greater sellable floor area;

 reduced utility bills; and

 more environmentally responsible materials.

With this range of benefits, thin brick can offer a strong and viable alternative to full brick. Why make the entire brick when the face is all that is really needed?

Notes

1Findings by the PCI committee’s three-year program to create a thin brick specification. Results are a combination of BIA and TCNA material characteristics.

2 Visit

3 Visit

Additional Information

Author

Randy Wilson is the national sales manger for MetroBrick, a division of Ironrock in Canton, Ohio. He has 17 years of experience in consulting with design/construction professionals and performing major construction project management. Wilson has an associate degree in architecture and construction management from OklahomaStateUniversity. He can be reached via e-mail at

Master Format No

03 40 00–Precast Concrete

04 20 00–Unit Masonry

07 40 00–Roofing and Siding Panels

09 30 00–Tiling

UniFormat No

B2010 Exterior Walls

C3010 Wall Finishes

Key Words

Divisions 03, 04, 07, 09

Concrete

Full brick

Thin brick

Abstract

An architect should realize the customer’s exterior wall needs prior to defining exterior finishes. When a masonry appearance is desired, thin brick wall assemblies have proven to increase owner value compared to traditional full brick cavity wall construction. The architect must fully understand the material and wall system differences to determine the best option for a project.

[VISUAL INFORMATION]

Figure 1

Appearance Classifications