Moisture Management

If it looks like stone and is a manufactured precast concrete product, then it must be cast stone, right? Wrong. What you are seeing may be adhered manufactured stone masonry veneer (AMSMV), architectural precast, calcium silicate, or even a natural stone. Each product has its appropriate applications that are dependent upon the situation. The following will provide a brief description of architectural cast stone and other related products.

Cast stone and other materials
Architectural cast stone is an architectural precast concrete building unit intended to simulate natural cut stone and used in unit masonry applications. As per ASTM C-1364, Standard Specification for Architectural Cast Stone, units must comply with a minimum of 6,500 psi compressive strength, less than 6 percent absorption (ASTM 1194 and 1195) and 5 percent cumulative percentage weight loss or less at 300 cycles for Freeze Thaw (ASTMC666). These requirements are applicable whether the product is manufactured by dry tamp, wet cast or machine-made methods. ASTM C-1364 is referenced in the 2012 International Building Code as the definition for cast stone and is, therefore, a legally binding in jurisdictions that have adopted the building codes. Any other industry specification is for reference only as an industry recommendation.

Cast stone is made from fine and coarse aggregates, Portland cement, sand, mineral oxide color pigments, chemical admixtures and water. It is distinguished by its fine surface texture and is available in virtually any color. It can be reinforced as needed to increase the structural integrity and is made from molds with precise measurements to make it easy for the mason to install on site. Lifting inserts, anchors, kerfs and drips can be cast into the stone, which reduces labor for the mason in the field. Because of these attributes, cast stone simulates a variety of types of natural stone including, but not limited to, limestone, granite, slate, travertine or marble.

Since cast stone is a heavyweight product, it is anchored into a wall system, and used as an architectural feature, trim, ornament or veneer on commercial and residential buildings and other structures. Applications for cast stone range from the simplest windowsills to the most complicated architectural elements, including use as a masonry veneer product. It is listed under Construction Specifications Institute (CSI) Masterspec in Division 04 72 00.

Architectural precast is a type of precast concrete that includes components ranging from massive panels to hand set units. Architectural precast has no ASTM designation, but relies on industry standards. A minimum strength of 5,000 psi, absorption of less than 6 percent is required with no freeze-thaw considered. Architectural precast tends to be made from course aggregates, sand, color pigment and Portland cement. The finish may show exposed aggregate and visible bug holes. It generally is specified for architectural panels, columns and large architectural elements and installed as a precast product as opposed to a masonry product. See CSI Division 03 45 00.

Column capitals, shafts, bases, arch mouldings and the fountain area all are made of Cast Stone.
Column capitals, shafts, bases, arch mouldings and the fountain area all are made of Cast Stone.

Limestone is a natural stone made from sedimentary rock that is formed by accumulation of organic remains (shells or coral), consisting mainly of calcium carbonate. Shapes are achieved by sawing or fracturing the stone, which has a fine grained texture. Grade II Limestone is specified as per ASTM C568, which requires a minimum 4,000 psi, less than 7.5 percent absorption and no freeze-thaw requirement is considered. It generally is used for architectural trim, facing and ornamentation and is not reinforced.

Calcium silicate masonry units are produced from sand and silica, which is mixed with hydrated lime and other elements. The no-slump mixture is then pressed into modular-sized molds and cured in an autoclave. Calcium silicate contains no Portland cement. The units produced can have a variety of textures and are used primarily as architectural veneer facing. Calcium silicate units must comply with ASTM C73 with MW Grade at 3,500 psi with maximum 14 percent absorption and SW grade at 5,500 psi with 11.6 percent maximum absorption. There is no freeze-thaw durability requirement and reinforcement is not available.

Adhered manufactured stone masonry veneer (AMSMV)  is a lightweight man made concrete masonry product which is usually cast into random sizes, in a variety of colors with a natural undressed quarried or cleft stone finish. Sometimes referred to as adhered veneer, AMSMV is generally applied on a residential or lightweight commercial structures for exterior and interior walls, landscape structures, and other structures suitable to receive lightweight adhered units. These simulated stone products are manufactured to meet CSI Division 04 73 00 classification for simulated stone. There are currently no ASTM standard specifications for AMSMV.

 

Cast Stone was used in the base of the buildings, stairways, terraces and garden ornamentation.
Cast Stone was used in the base of the buildings, stairways, terraces and garden ornamentation.

Sustainability benefits of architectural cast stone
An important part of construction today is the sustainability or “green” component of the building. Each product used in the building contributes to the overall impact on the environment. The following are just some of the sustainable attributes of cast stone.

The durability of cast stone enhances the longevity of the building which provides economic benefit to the owner and the community.

Cast stone can also contain recycled materials, such as recycled glass or other recycled aggregates, coloring pigments made from post-consumer recycled materials, synthetic fibrous reinforcement made from 100 percent post-consumer recycled materials and steel reinforcement with high recycled content.

Cast stone is manufactured and delivered to the jobsite in the exact quantities needed for the project, with almost no construction waste as a result. Any waste that is produced may be crushed and used as recycled aggregate or fill.

Requires minimal to no maintenance or repair which also contributes to the life cycle cost of the building and conserves resources.
Numerous cast stone production locations throughout the United States help to meet code and rating system requirements for locally produced product.

The high thermal mass properties of cast stone help optimize the energy performance of a building and mitigate temperature swings.

The high Solar Reflective Index (SRI) of cast stone helps reduce heat retention and urban heat island effect. Typically manufactured with white Portland cement, cast stone provides an assumed SRI of 86 for a non-pigmented mix.

Low Volatile Organic Compounds (VOC) emissions support indoor air quality strategies.

As a masonry product, it can be installed using local skilled mason labor.

Cast Stone Institute
As a non-profit trade association, the Cast Stone Institute was formed in 1927 for the purpose of improving the quality of cast stone and disseminating information regarding its use. Institute Technical specifications, bulletins, details and related materials are available for free download from www.caststone.org.

The most important valuable resource to specifiers is our Certified Producer Members, who adhere to the high standards for quality and are bound by a strict code of ethics. Members must provide testing of product every 500 cubic feet for compression and absorption, as well as independent laboratory test results every six months to confirm their product meets the Institute standard specification and ASTM C1364. They must also have a current compliant freeze-thaw test.

These tests are mandated by ASTM C1364, and members comply with these strict regulations and provide proof of compliance to the Institute every six months. Since the products that go into the mix design for cast stone come from the earth, there can be variances in sands, aggregates, etc. Testing assures the Producer Member, the specifier and owner that they are, indeed, producing cast stone to specifications. There is no way to assure quality cast stone production without this testing.

Cast Stone Institute certification differs from others in that they certify that not only the processes are in place to make quality product but that the product itself is meeting specifications. All Certified Cast Stone Institute Producer Members provide a 10-year Limited Product Warranty for the cast stone they supply on projects.

Conclusion
The use of architectural cast stone allows an architect to design a masonry building and put his signature on it by creating detailed architectural elements that can be manufactured easily and affordably by a Certified Cast Stone Institute Producer Member.

Historic structures can be restored by using cast stone to replicate the original stone on the building for numerous applications including detailed ornamentation. The mason is the craftsman who puts the pieces of the puzzle together to make a beautiful structure that will enhance the community for decades to come.

Installation 101

Chris HinesInstalling Manufactured Stone Veneer

As a non-structural element of a building’s exterior, manufactured stone veneer can add significantly to the aesthetics and perceived value of a structure. As a lightweight, architectural, non-load-bearing building product, it is manufactured of lightweight concrete material and mimics the visual appeal of stone found organically in nature. However, since it is so lightweight, it is extremely easy to install.

Here are some of the dos and don’ts for the successful installation of manufactured stone veneer.

  • Evaluate the project before you start (even before you bid). Look for properly gapped sheathing material, bowed studs or out of square corners needing correction, and proper window and door installation and flashing. If it’s a masonry substrate, assure it is structurally sound, clean, rough and capable of bond.
  • Prepare the wall with the right materials, installed correctly. A list of industry-accepted materials, installation instructions and details are available at www.masonryveneer.org.
    1. If the wall requires a water-resistive barrier (WRB), select a material that suits the climate, installation timing and building style.
    2. Framed applications require a weepscreed or other flashing at the foundation termination to protect susceptible materials and allow liquid water to exitthe system. Maintain appropriate clearance at the bottom of the wall. 
    3. When Lath is required, run the sheets, cups up, horizontally and overlap sheets at least one inch or greater, if required by the manufacturer. End lath sheets at framing locations. Never terminate at a corner. The material must run through the corner to a framing member. Select fasteners that are long enough to penetrate into framing by at least one inch. 
    4. Take the time to mark framing at every step.
    5. Lath materials should be furred off the wall ¼-inch, to allow proper mortar embedment. Apply your scratch-coat mortar with sufficient force to key into the lath.
  • Select a mortar that meets MVMA recommendation. Understand the properties, mixing and usage requirements of your mortar to ensure a strong bond. Assure stone units are set in a full setting bed of mortar.
  • Work clean. Some stones may be installed from the top, down, to avoid mortar dropping. If you experience mortar droppings on the face of a stone, wait until it’s crumbly and brush off.
  • Lay out stones and mix boxes. Take the time to lay your stones out. Understand the colors, shapes, sizes and textures and blend them. Periodically step back, view and adjust.

  • Don’t use WRBs intended for roofing on walls.
  • Don’t install over someone else’s work if it wasn’t done properly.
  • Don’t skip flashing steps. Water management is key with any cladding system.
  • Don’t install over ripped or missing WRBs.
  • Don’t end lath in or on corners.
  • Don’t install over an extremely smooth concrete surface without first making it rough.
  • Don’t install stone veneer on stair treads, risers or other areas likely to be exposed to walking friction, kicking, de-icing chemicals and bad water drainage.
  • Don’t disregard clearance from grade requirements. You will risk spalling damage, bad appearance from efflorescence and staining, potential moisture deterioration and void warranty coverage.
  • Don’t use installation materials that are not addressed in the MVMA Installation Guide.
  • Don’t cap walls or veneer sections with less than a one- to two-inch overhang beyond the thickest stone in the veneer texture.

If these guidelines are followed, manufactured stone veneer application will provide long-lasting performance and remain visually appealing, increasing the value and visual attractiveness of a building.


Chris Hines is technical leader of Boral Stone Products.
Product Spotlight

Oldcastle Architectural’s Cordova StoneOldcastle Architectural, a producer of concrete masonry products, has renamed its high-density, pre-finished architectural concrete masonry unit Cordova Stone.

Oldcastle says the rebrand is part of extensive research and development in artisan stone veneers. The adoption of the Cordova Stone name signifies the end of the company’s sale of the product under the PRAIRIE STONE mark. The new name is intended to more accurately express the unit’s artisan aesthetic and natural stone beauty. The company plans to unveil additional artisan product offerings in the coming months under the Artisan Masonry Stone Veneers brand.

Manufactured by Northfield Block, an Oldcastle company, Cordova Stone uses all-natural aggregates and can be cut and shaped in the field. Other than routine cleaning with a standard commercial-grade cleaning agent, Cordova Stone masonry units require virtually no maintenance and will last the lifetime of your building. Manufactured with a water repellent admixture, Cordova Stone masonry units repel moisture, resist mold and offer efflorescence stain resistance.

For more information, call (855) 346-2766 or visit www.oldcastlearchitectural.com.



Last Updated on Thursday, 16 August 2012 21:46