Selecting manufactured stone veneers

by Katie Daniel | September 18, 2017 2:48 pm

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by Jim Cooper
For construction projects ranging from residential homes to light-commercial projects such as healthcare centers, retail buildings, and senior living facilities, manufactured stone veneers offer cost savings, quick installation, and opportunities for eye-grabbing aesthetics.

Rather than having a less appealing painted-block finished exterior, some communities are demanding both remodel projects and new construction blend into local surroundings. Government-approved ordinances are also having a huge impact. This is where stone veneer comes into play—new technology in masonry can help achieve desired outcomes at lower cost and with improved visual performance over some traditional assemblies.

Choices in manufactured stone veneers have expanded, lending both performance and customized aesthetic advantages. At the same time, the manufacturing processes to achieve certain performance characteristics have greatly advanced. What do design professionals need to know?

Technology advances and performance
Traditionally, both lightweight and full-depth stone veneers have been manufactured through a wet-cast process using latex molds for lightweight veneers. In wet casting, natural stones are arranged in a pattern, with latex sprayed on them to create a mold. When it comes time to cast the veneers, the molds are hand-painted with a colorant specified to resemble a particular variety of stone.

The resulting veneers are only colorized on the outermost layer. This means if the veneers are chipped accidentally, or purposely cut during installation, the non-colored aggregate on the interior becomes exposed. Additionally, special corner and trim pieces are needed to obtain finished, ‘real stone’ looks without sacrificing color consistency.

By comparison, a new mold technology known as the dry-cast production method can create products with longer lifespans and better dimensional stability. The proprietary processes are similar to paver technology, beginning by scanning natural stone and turning those scans into patented steel mold forms. A low-moisture mixture of fine aggregates, cement, admixture, and integrated colorant are densely compacted into the molds, then stripped from them and cured in a high-humidity environment. The resulting veneers contain only about six percent moisture, whereas moisture content in wet-cast can be upward of 33 percent. This mixture also contains water repellents and uses 40 percent less water than wet-cast methods. This means dry-cast stone is more resistant to the de-icing salts applied on sidewalks, whereas as wet-cast stone tends to soak them in and, potentially, disintegrate.

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Dry-cast veneers are perfect for ashlar, stacked, and square applications requiring a stacked look, while resisting freeze-thaw stresses, water absorption, and fading at significantly less cost than their wet-cast counterparts. They are well-suited for residential, retail, and light-commercial construction given their speed of installation and versatility.

Additionally, the lightweight and full-depth veneers that are manufactured through dry casting offer a compressive strength two to three times greater than traditional wet-cast veneer. A dry-cast product averages 34,475 kPa (5000 psi), whereas wet-cast only approaches 13,790 kPa (2000 psi).

Although both dry- and wet-cast manufacturing processes face the same outdoor challenges, the former, with its higher compressive strength and water repellents, will absorb less moisture. It will also have a greater resistance to freeze-thaw issues, and be significantly less impacted by de-icing salts.

The dry-cast veneer process can create colors, textures, widths, and profile sizes similar to natural stone, enabling the two materials to be used together. Further, having color integrated throughout the unit (including finished ends) eliminates the need for special corner pieces and reduces waste caused by chipping. The question is, when might one specify a lightweight or thinner profile versus a full-depth one?

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Full-depth vs. lightweight veneers
Choosing full-depth or lightweight veneers can vary by personal taste and comfort level, and largely depends on the application. Wall height can be a factor as well. Some design professionals are less comfortable with having adhered manufactured lightweight veneers installed on high walls, given the rare possibility one might come loose. In such an application, the builder or retailer may prefer to spend more on a cavity wall to accommodate a full-depth anchored veneer, which is typically 92 mm (3 5/8 in.).

Lightweight veneers will frequently be chosen as economical façades in applications such as retail buildings or senior living facilities because mixed-material looks for siding, stucco, and stone foundation façades and accents are a popular trend.

Another possibility for dressing up a light commercial building is to blend manufactured stone and brick. A sill is typically required to separate the materials, but the bed depth can accommodate a set-in product like full-depth veneer. However, the cost is higher than an adhered application. Stone veneers are easy to match to natural stone, which can be cut to the same width as a full-depth or thin veneer.

Manufactured stone veneer color choices
When measuring wet- versus dry-cast advantages, one should consider colors for dry-cast can be customized before arriving onsite. This can be especially important for structures opting for a more architecturally distinctive structure than a traditional retail building. For example, a recent large-scale, 3700-m² (40,000-sf) museum in Kansas, designed by Jonathan Kharfen, AIA (Boston’s Verner Johnson Architects), used this customization option to match colors in the natural environment. The project saved significant cost by blending manufactured full-depth veneers with locally sourced stone onsite in the way the architect desired.

For national retailers, manufactured stone veneers add speed and economy to the building process, while also effectively dressing up the building as compared with painted block. For example, a popular trend for retail is to combine integral colors of split-face block with manufactured structural concrete masonry units (CMUs) and stone or brick veneer at half the price of a traditional cavity wall.

As aesthetics in communities come into play, more retail buildings are adopting the mixed-material veneer look, which will likely be manufactured stone—either thin or full-depth, based on cost. Smaller retailers, condos, hotels, and senior living facilities are going in this direction to blend in with the community and meet local ordinances.

The growth of senior living facilities (due to the aging baby-boomer population) provides a prime example of making a residence building feel like home, both on the exterior and interior. These structures are typically one to five stories, with
a band of stone veneer around the lower level and stucco or siding on the upper wall. Manufactured lightweight veneers can provide beautiful textures and colors in these applications, but with much higher performance and lower moisture and cost than other materials.

For light-commercial application exteriors, it pays to look at the overall project—what are the aesthetic needs, thermal and moisture considerations, and
de-icing chemicals used? For long-term performance, dry-cast manufactured stone veneers provide easy installation, fewer headaches, significant cost savings, and simple installation.

As more and more jurisdictions mandate continuous insulation per the 2015 International Energy Conservation Code (IECC), lightweight veneers offer another advantage—they can be installed atop such assemblies, with builders using longer screws for the wire mesh going into the studs.

MEETING LEED V4 WITH MASONRY

Voluntary programs such as Leadership in Energy and Environmental Design (LEED) have joined with new building code requirements to reinforce holistic approaches to the entire building process. The new LEED v4 program is a significant revision from the previous 2009 edition. It calls for specific performances that can be met with concrete masonry units (CMUs). Increased energy efficiency In LEED v4, buildings must be at least five percent better than American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2010, Energy Standard for Buildings Except Low-rise Residential Buildings, with whole-building energy simulation as the preferred compliance path. Masonry can add increased R-values to energy performance. Thermal mass Thermal mass, as found in masonry products, absorbs energy slowly and stores it for longer periods. This reduces indoor temperature swings and often leads to a reduction in the size of mechanical heating and cooling systems. Material ingredients matter Three entirely new credits in the LEED v4 Materials and Resources (MR) section require documentation of building product raw materials and their effects on the environment, such as material ingredient reporting, health product declarations (HPDs), and environmental product declarations (EPDs). Several concrete masonry unit (CMU) manufacturers have published such information on their products. Product sourcing Other new MR credits include sourcing of raw materials and a new take on regional materials that eliminates the standalone credit and instead adds weight to products sourced within 160 km (100 mi) of the project site. Manufactured masonry can often be sourced within this distance. Consideration of building life cycle added Expanded credits include reusing existing buildings and a new credit on performing a whole-building life cycle assessment (LCA). Masonry buildings provide a long life and durability that are essential for reuse. Acoustic performance LEED v4 now includes a prerequisite for minimum acoustic performance in schools and a credit for acoustic performance in most other versions of the rating system. Manufactured masonry can enhance acoustical performance, evidenced by its recent use in public theaters. Christine A. Subasic, PE, LEED AP, is a consulting architectural engineer specializing in masonry and sustainable design. She has provided technical support services, standards development, and seminars for the masonry industry for more than 25 years.

Jim Cooper is the national director for Artisan Masonry Stone Veneers, which is part of the Echelon Masonry portfolio of products from Oldcastle Architectural. Prior to his role with Oldcastle, he worked for a wet-cast manufacturer as a national sales manager. Cooper can be reached via e-mail by writing
to jim.cooper@oldcastle.com[4].

Source URL: https://www.constructionspecifier.com/selecting-manufactured-stone-veneers/

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