Articles Regarding Cast Stone
 

ARCHITECTURAL CAST STONE – VERSATILE, ROBUST, & SUSTAINABLE - Published Article, August 2012
By Jan Boyer, Cast Stone Institute^® Executive Director

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If it looks like stone and is a manufactured precast concrete product, then it must be Cast Stone. Not true. 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 which are dependent upon the project. 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% absorption (ASTM 1194 & 1195) and 5% 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 heavy weight 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% is required with no freeze thaw considered. Architectural Precast tends to be made from course aggregates, sand, color pigment & Portland cement. The finish may show exposed aggregate and visible bug holes. It is generally 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.

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% absorption and no freeze thaw requirement is considered. It is generally 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 a 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% absorption and SW grade at 5,500 psi with 11.6% 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.
 

SUSTAINABLE 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% post-consumer recycled materials and steel reinforcement with high recycled content.
• Cast Stone is manufactured and delivered to the job-site 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 USA 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.

ABOUT THE 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 the website 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 ft. 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 are tests mandated by ASTM C1364 and our 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. Without this testing, there is no way to assure quality Cast Stone production.

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.
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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 easily and affordably manufactured 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.
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Author: Jan Boyer is the Executive Director of the Cast Stone Institute since 2006. She serves on the Board of Directors for The Masonry Society and the Masonry Alliance for Codes & Standards. Involved in the masonry industry for over 14 years, she is also affiliated with the Concrete Joint Sustainability Initiative and the State Alliance of the National Concrete Masonry Association. She can be reached at jboyer@caststone.org or by calling 717-272-3744.

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RESTORING HISTORIC STRUCTURES with CAST STONE - Published Article, May 2012
By Jan Boyer, Cast Stone Institute^® Executive Director

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As the magnificent historic buildings across America are aging, restoration will be required to maintain and save these structurally sound buildings rather than demolish and rebuild. No matter what the natural stone or concrete based material originally used on the building, cast stone is the natural choice for the restoration efforts due to the unique capabilities of the product and the craftsmen producing cast stone. The following case studies show just how versatile cast stone can be to turn restoration challenges into beautiful realities.

714 Main Street – Farmers & Mechanic Building
Ft. Worth, Texas
This project involved restoration of a historic 200,000 sq. ft. office tower originally built in 1920 and located at a popular crossroads in the downtown center. It involved replacing various veneer materials, both terracotta and GFRC, with cast stone on the first two stories. The building was originally ornamented with heads of Roman Soldiers at the second floor level as palace guards. In previous renovations of the structure, the heads of the Roman Soldiers were removed. The only remaining historical reference was old photographs. In order to reproduce the Roman Soldier heads in cast stone, original artwork was produced then a series of molds were made. The molds required significant detail that included the facial expression and the final product was reviewed by historians for accuracy.

The veneer pieces that formed the remaining parts of the exterior of the first two stories were challenging to produce as in many cases they had to form around the large heavy weight soldier heads. This visual challenge to achieve the look of the original terra cotta was met by adding black blasting material to the batch design.

The detail and the exacting design of the Roman Soldier heads in accordance with original pictures was the primary goal of this project. Cast Stone and casting techniques were critical in providing the detail necessary to restore this building to its original conception.

Princeton University Press
Princeton, New Jersey
Showing that cast stone is also perfect for structural applications, this hardscape restoration project involved replication of a collegiate gothic courtyard entrance, originally erected in 1911. The extreme detailing and massiveness of the piece as well as replicating the original exposed aggregate in the cast stone elements made this an extremely interesting project.

The scope of the project included the complete replacement of the existing ornate cast stone structure including the jambs, radius arch with rosettes, decorative panels, towers, and coping. In order to accomplish the original intent, the cast stone arch was fabricated as a one-piece design and was structurally engineered to support the loads of the opening. This significantly reduced the installation cost and timeframe.

The molding process was extremely complex, as the one-piece cast stone arch incorporated numerous architectural details including rosettes, surround profiles, decorative panels, and false joints all into the same mold. Therefore, the mold was fabricated out of a combination of materials including, wood, fiberglass, and rubber, in order to be able to replicate the fine architectural details, as well as to be able to “de-mold” the element after casting.

“Cast stone was also effective in terms of flexibility in design. We [the project team] were able to make design changes and improvements that we would not have otherwise been able to do with natural stone”, said Jeff Frake of Masonry Preservation Group.

Joseph P. Kinneary Federal Courthouse
Columbus, Ohio
“Cast stone was also effective in terms of flexibility in design. We [the project team] were able to make design changes and improvements that we would not have otherwise been able to do with natural stone”, said Jeff Frake of Masonry Preservation Group.

Built in 1934 with funding from President Franklin Roosevelt Public Works Administration economic recovery program, the entire façade of the building is sandstone taken from a quarry in northern Ohio in 1932. The huge seven story building is in the process of a complete exterior renovation with cast stone replacing the original sandstone. The Ohio Historical Society is involved with the project, along with the architect, to ensure that the cast stone is produced in such a manner that it will be an exact match to the existing sandstone to maintain the integrity of the original design.

Phase one of the restoration has begun involving the replacement of the sandstone on the top three floors with cast stone, the material of choice because of its versatility in color, texture and shapes for the stones. To ensure that the texture was correct, multiple pieces from the building were delivered to the cast stone manufacturer’s plant then castings were made from each of them. The samples made from the castings show the striations and blending of colors in the cast stone to create just the right look. In addition to color and texture, each original stone, when removed from the building, is numbered, a mold produced and stone cast with exactly the same look and size as the original.

To add to the complexity of the project, the Federal Courthouse will continue to be in session requiring all of the work to be performed from 6:00 PM to 4:00 AM only. This includes everything from demolition and shipments to installation. Given the location in downtown Columbus, one elevation is bordering a river, two elevations have road frontage, and one elevation has a city park connected to the property. The location also affords very little on site storage so communication among all team members is vital.
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These are just a few of the myriad of projects already restored with the use of cast stone. When considering a producer of Cast Stone for your next project, log onto www.caststone.org for a listing of certified producer members of the Cast Stone Institute^® who take pride in the relentless pursuit of excellence for every project. While you are on the website, take a moment to review the photos section for other award winning projects and further information about cast stone and the Cast Stone Institute^®.
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Author: Jan Boyer is the Executive Director of the Cast Stone Institute since 2006. She serves on the Board of Directors for The Masonry Society and the Masonry Alliance for Codes & Standards. Involved in the masonry industry for over 14 years, she is also affiliated with the Concrete Joint Sustainability Initiative and the State Alliance of the National Concrete Masonry Association. She can be reached at jboyer@caststone.org or by calling 717-272-3744.

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Cast Stone Institute^® Education Opportunities - Published Article, January 2012
By Jan Boyer, Cast Stone Institute^® Executive Director

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The Cast Stone Institute^® recognizes that, because cast stone is not included many times in the training of specifiers or masons, there is confusion as to the properties of the product as well as the appropriate construction practices. True to its mission to improve the quality of cast stone and disseminate information regarding its use, the Institute provides information about technical aspects of the product and has produced seminars to train on the properties and best practices for placing cast stone to ensure long durable life on the building. Institute technical specification, bulletins, details and related material are included individually and in the Cast Stone Institute Technical Manual available for free download from the website www.caststone.org.

The following seminars are available through the Institute to train mason contractors and architects on best practices:

Architectural Design with Cast Stone
In this general information seminar, you will learn how Cast Stone is made, how it differs from related precast and natural stone materials and the testing requirements for cast stone as per ASTM that include a freeze thaw requirement. The applications, design recommendations and appropriate specification of Cast Stone for architectural applications will be discussed. Do's and don'ts for appropriate design and placement of the stone is reviewed. The sustainable attributes of Cast Stone related to LEED and green building will also be discussed.

Cast Stone Connections
In this detailed seminar, the common terminology, design and installation techniques for interior and exterior architectural applications and anchoring for veneer applications of Cast Stone will be taught. Attendees will understand the common exterior veneer installation methods as well as guidelines for stacked or relief supported cast stone veneer, rebated anchors, mechanical cladding systems, appropriate wall ties, back anchors, kerfs, shims, mortar joints, sealant joints and caulking options. Additionally, industry codes and regulations as they relate to proper cast stone details and setting will be reviewed.

Jobsite Handling & Installation
This seminar is geared specifically toward mason contractors and field supervisors to address field practices for the proper handling of architectural cast stone. It addresses shop drawings, sample approvals, shipment and on site storage, tolerances, cold weather setting practices, flashing, weep holes, sealant joints, protection after setting and touch up.

These seminars are available for presentation to local, regional or national mason groups. Contact the Cast Stone Institute office to arrange for a CSI Certified Producer Member to make the presentation.

All Certified CSI Producer Members must pass a rigorous certification that checks for outstanding quality control, safety procedures, consistency of product, meticulous record keeping and many other manufacturing processes which are involved in the production of high quality cast stone elements. In addition, members must provide testing of product every 500 cubic ft. 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. This required testing assures the Producer Member, the specifier and owner that they are indeed producing cast stone to specifications. Without this testing, there is no way to assure quality cast stone production.

Cast Stone Institute^® Producer Members must also undergo the recertification process every two years by unannounced plant inspections performed by an independent engineering firm in order to assure compliance to requirements. The 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. They each provide a 10 year Limited Product Warranty for the cast stone they supply on projects.
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For more information about the Cast Stone Institute^® log onto www.caststone.org or contact the office by calling 717-274-3744 or email to staff@caststone.org.

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SPECIFYING CAST STONE - Published Article, April 2011
By Jan Boyer, Cast Stone Institute^® Executive Director

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Cast Stone has a bit of an identity problem. You see, it makes sense that any material that replicates natural stone is cast stone. If it looks like stone and is a manufactured product, then it must be cast stone. Not true. It could be Adhered Manufactured Stone Masonry Veneer (AMSMV), architectural precast, calcium silicate, or even a natural stone. On many construction documents today, there is confusion in both terminology and physical properties when a material is called out as cast stone, adhered stone veneer or architectural precast. Each product has its appropriate applications dependent upon the project. How can you determine the difference so that you are specifying the correct product for the building application?

CAST STONE AND OTHER MATERIALS
Adhered Manufactured Stone Masonry Veneer (AMSMV) is a light-weight architectural non-load bearing product produced from a wet cast blend of cementitious materials, lightweight and other aggregates, iron oxide pigments and admixtures. It is sometimes referred to as simulated stone or adhered veneer and usually cast into random sizes, in a variety of colors with a natural undressed quarried or cleft stone finish. AMSMV is generally applied as a residential or lightweight commercial masonry veneer adhered to exterior and interior walls, structures, columns, landscape structures, and other structures suitable to receive lightweight adhered units. These simulated stone products are manufactured at 1,800 to 2,000 psi with 22% (UBC Standard 15-5) absorption to meet Construction Specifications Institute (CSI) Division 04 73 00. There are currently no ASTM standard specifications for AMSMV.

Architectural Precast is a wet cast architectural unit made from coarse aggregates, grey or white cements, sand and color pigments manufactured to meet CSI Division 03 45 00. According to this specification, it must be a minimum of 5,000 psi and 6% absorption with no Freeze Thaw durability requirement. It is generally specified for architectural panels, columns and large architectural elements and installed as a precast product as opposed to a masonry product.

Cast Stone is defined as “a refined architectural concrete building unit manufactured to simulate natural cut stone, used in unit masonry applications and is manufactured to meet Division 04 72 00 requirements. Used as an architectural feature, trim, ornament or facing for buildings or other structures, it is created with a fine grain texture to simulate all types of natural cut stone including but not limited to limestone, granite, slate, travertine or marble. Cast Stone can be made from white and/or grey cements, manufactured or natural sands, carefully selected crushed stone or well graded natural gravels and mineral coloring pigments to achieve the desired color and appearance while maintaining durable physical properties which exceed most natural cut building stones. Cast stone is generally built into a load bearing masonry wall system in traditional commercial and residential buildings and other structures. It is specified as per ASTM C1364, Standard Specification for Architectural Cast Stone that was originally approved in 1997.

Cast Stone requirements in ASTM C1364 are:

• Compressive Strength - ASTM C1194: 6,500 psi minimum for products at 28 days

• Absorption - ASTM C1195 of 6% maximum by the cold water method, or 10% maximum by the boiling method for products at 28 days

• Air Content – ASTM C173 or C 231, for wet cast product shall be 4-8% for units exposed to freeze-thaw environments. Air entrainment is not required for VDT products

• Freeze-thaw – ASTM C1364: of less than 5% after 300 cycles of freezing and thawing. Of note is that Cast Stone is the only product with a freeze thaw requirement that must be met by all manufacturers.

Cast Stone generally is a higher quality finish than other types of precast products. It has a fine grained texture and is used as architectural trim, veneer facing and ornamentation in unit masonry.

In order to clarify the use of Cast Stone it was ultimately determined that the correct ASTM designation, ASTM C1364, be referenced in the International Building Codes.

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CAST STONE NOW AS PER ASTM C1364 IN BUILDING CODES
The International Code Council (ICC) Family of Building Codes, including those for all structures, residential and others, have now been adopted in most States. These Codes are legally binding and supersede any other specification unless referenced in these documents. So what does this mean for Specifiers?

Most all materials in the Codes are referenced by definition and as per their ASTM number. In the past, Cast Stone was referenced by definition only as a material that replicated natural stone with no ASTM requirement. This allowed for other products to be referenced in the Code under Cast Stone when it was not the same material.

The Cast Stone Institute ®, through the efforts of the Masonry Alliance for Codes and Standards, forwarded a Code Change proposal to the ICC to require that Cast Stone be defined by, and comply with the requirements of ASTM C1364 in the International Building Code. This proposal was voted at the final action hearings in May 2010 and adopted. It will be included in the 2012 International Building Code (IBC) which is available for distribution as of April 2011.

This is important as it means that Cast Stone specified on a project must comply with all of the ASTM C1364 standards – including freeze thaw requirements.

Each of these materials is referenced in the IBC by the appropriate category and Chapter. Cast stone is referenced under the Masonry Section. As the International Residential Code references the IBC for terminology, the ASTM C1364 reference applies to residential structures as well.

ABOUT THE CAST STONE INSTITUTE®
As a non-profit trade association, the Cast Stone Institute ® (Institute) was formed in 1927 for the purpose of improving the quality of cast stone and disseminating information regarding its use. Today our mission remains, not only to be the authoritative spokesperson for Cast Stone, but also to provide expert counsel to the architectural and engineering communities. The activities of the Institute are designed to benefit both the industry and its patrons. Institute Technical Specification, Bulletins, Details and related material are included in the Cast Stone Institute Technical Manual available for free download from the website 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. Prior to membership approval by the Institute Board of Directors, all potential producer members (manufacturers) must have been manufacturing cast stone for a minimum of three years and pass a rigorous certification that checks for outstanding quality control, safety procedures, consistency of product, housekeeping, meticulous record keeping and many other manufacturing processes which are involved in the production of high quality cast stone elements. In addition, members must provide testing of product every 500 cubic ft. 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 are tests mandated by ASTM C1364 and our members comply with these strict regulations and provide proof to the Institute of this compliant test data 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. Without this testing, there is no way to assure quality cast stone production.

Cast Stone Institute® Producer Members must also undergo the recertification process every two years by unannounced plant inspections. This unannounced inspection is performed by an independent Engineering Firm in order to assure compliance to requirements. The 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.

CAST STONE INSTITUTE PRODUCER MEMBER 10 YEAR LIMITED PRODUCT WARRANTY
As of January 1, 2011, all Certified Cast Stone Institute Producing Members provide a 10 year Limited Product Warranty for the Cast Stone they supply on projects.

Continuing to lead the industry, the Cast Stone Institute® Producer Members voted on October 8, 2010 to adopt the language for a 10 year Limited Product Warranty. Institute Producer Members are aware of the evolving environment for products in the marketplace that demand sustainability, durability and useable service life. This warranty demonstrates that they embrace these principles and produce product that will stand the test of time.

CONCLUSIONS
What does all of this mean for the specification of cast stone?

• All Architectural Cast Stone must meet ASTM C1364 including test data and freeze thaw durability as per the 2012 International Building Code.

• Certified Cast Stone Institute Producer Members are required to comply with ASTM C1364 and provide the test data to back this up.
   
• The 10-year Warranty provided by Cast Stone Institute® Producer Members.

Certified Producer Members of the Cast Stone Institute are engaged in the relentless pursuit of excellence in manufacturing. The results of these efforts include consistently high product quality, through continuous improvement in manufacturing methods and materials, and the assurance that Cast Stone Institute Certified Producer Members are keeping cast stone a premier building material. Properly manufactured, designed and installed, cast stone can result in an architectural project of enduring beauty to be enjoyed for decades. When specifying cast stone on a project, be sure to call out for a Cast Stone Institute Member and hold to that specification. This provides Specifiers and Owners the quality assurance the project deserves.

For more information, log onto www.caststone.org.

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Cast Stone Dilemma - Published Article, July 2009
By Gary Fry

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Make the cream rise to the top!

Cast Stone is alive and well in these challenging times. But—the construction industry struggles to maintain its’ equilibrium as the nation’s economy is challenged and many markets shrink. If the purchaser succumbs to the temptation of making the decision based solely upon price it is more than likely that they will face a dilemma with the resultant process. It’s a good time to think about basics.

Cast Stone is a premier masonry product that provides ornamental or functional features to buildings and other structures. It gives the appearance of a variety of natural building stones and applications range from the simplest windowsills to the most complicated architectural elements. Properly manufactured, it has the same or stronger physical properties as most dimensional building stone. In essence Cast Stone is a highly refined architectural precast (concrete) product manufactured to simulate natural cut stone. Concrete is a very basic building material that adequately serves a multitude of construction applications. The ingredients are readily available and the skills required to make concrete are relatively simple. So, what does “highly refined” mean? Basically, it means manufactured in compliance with a set of standards.

The recognized standard for Cast Stone is ASTM 1364 Standard Specification for Architectural Cast Stone which requires a compressive strength greater than 6,500 psi as per ASTM C1194 test and maximum absorption rates of 6% and 10% for cold water and boiling methods, respectively as per ASTM C1195 test. The Cast Stone Institute requires Producer Members to comply with these specifications as well as ASTM C 666 – Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing. Also referenced within the ASTM C 1364 are a myriad of ASTM standards that regulate the ingredients of cast stone, such as cement, aggregates, reinforcing, color, etc…

Concrete, and therefore cast stone can be a very fickle product, as evidenced by examples of failure in diverse applications. These failures are most predominately caused by human actions rather than ingredients. So, while it is a good start to assure compliance of ingredients with these standards, it is not enough. Additional standards regulate forming, mixing, placing, finishing, curing, storage, etc… It is prudent that producers follow these “basics” and document compliance in order to verify performance to the purchaser. That means keep records verifying test results and have certifications on-hand for all materials.

Cast Stone has been a prime building material for hundreds of years.
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The earliest known use of Cast Stone dates about to the year 1138 and was seen at Carcassonne, France, the Cité which contains the finest remains of medieval fortification in Europe. Cast Stone was first used extensively in London in the year 1900 and gained widespread acceptance in America in 1920.

Today, Cast Stone is a truly superior alternative to natural cut building stone. Combined with its ability to simulate or reproduce an almost limitless variety of natural stones, Cast Stone offers many advantages over cut stone. Cast Stone can be integrally reinforced with steel and precisely colored through aggregates or mineral oxides. Mix designs have tested engineering values which result in a predictable durable life. Strength and weathering qualities are consistently better than natural stone because the manufacturing process is controlled. Properties such as these cannot be assured in a quarried building stone. Repetitive treatment, either as trim or ornament, can be achieved quite economically in Cast Stone. The ability of Cast Stone to replicate deteriorating natural stone on existing buildings makes it an ideal material for the remodeling or restoration of old structures.

Typical cast stone elements include modular base panels, water table, sills, jambs, heads, keystones, door surrounds, cornice, pier caps, coping, band course, balustrade, stair treads & risers, plaques, quoins, signs, and columns.

Several manufacturing processes have been utilized in the storied history of cast stone, with mixed results. Modern cast stone is almost exclusively produced by the three processes defined by CSI Specification 04-72-00-04

• Vibrant Dry Tamp (VDT) casting method: Vibratory ramming of earth moist, zero-slump concrete against a rigid mold until it is densely compacted.

• Machine casting method: Manufactured from earth moist, zero-slump concrete compacted by machinery using vibration and pressure against a mold until it becomes densely consolidated.

• Wet casting method: manufactured from measurable slump concrete and vibrated into a mold until it becomes densely consolidated.

The Cast Stone Institutes Technical Manual has become the most widely accepted standard for the industry. Most specifications will defer to the requirements for cast stone expressed in its standard specifications.

CSI’s contemporary initiatives address the challenges that most businesses struggle with during such an economic climate, providing accountability for the manufacturing process and offering added value to the end-user. Jan Boyer, Executive Director, believes " Leadership for a national trade association requires the vision to look for opportunities that will: set your members above others in the industry, create and maintain market share, work with related associations toward common goals and much more. The Cast Stone Institute believes in partnering within the cement based products & masonry industries to work toward the common goals of appropriate sustainable development as a socially responsible initiative as well as building codes and standards that correctly specify our product toward building a safe, secure environment for communities."

topDilemma - a situation in which somebody must choose one of two or more unsatisfactory alternatives.

There is an axiom that says “Things equal to the same thing are equal to each other.” In order for the product of a non-certified plant to be compared (equal) to that of a certified plant it is reasonable to require verification of compliance with the usually requisite ASTM C 1364. To not do so is to risk ending up with an unsatisfactory alternative.

The cream will rise to the top! Quality cast stone producers and masons will do the right things during these challenging times because they are competent and understand that short cuts cost more in the long run and are self destructive. The purchasing decision must follow suit and provide quality product that has been manufactured in compliance with the appropriate standards. The purchaser best serves his requirements by including product in the list of choices that is demonstrably capable of fulfilling all of his requirements, not just those in the short run.

Author: Gary Fry is immediate Past President of the Cast Stone Institute, and has held the offices of Secretary/Treasurer and Vice President. Upon his retirement recently from Sun Precast Company he was elected as an Honorary Member of CSI and continues to serve the Membership and Ethics committees. His 11 year tenure at Sun Precast as Vice President and President/CEO followed a diverse background in general construction and manufacturing. Gary resides in Milton, Pa. and enjoys a full schedule of golf, fishing, and animal rescue, as well as advocating for Cast Stone and Lean Manufacturing.



Cast Stone Vs. Adhered Veneer - Published Article, September 2008
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Submitted 9/16/08
For publication - Feb 2009 Masonry Construction Magazine

The Difference Between Cast Stone and Adhered Manufactured Stone Masonry Veneer

by Bill Russell
Chairman, Cast Stone Institute Committee on Educational Standards

On many construction documents today, there is confusion in both terminology and physical properties when a material is called out as cast stone or adhered stone veneer. This article attempts to clarify the differences in the two products.

DEFINITIONS
Cast Stone is defined as “a refined architectural concrete building unit manufactured to simulate natural cut stone, used in unit masonry applications.” Cast Stone is a masonry product, used as an architectural feature, trim, ornament or facing for buildings or other structures. It is created to simulate all types of natural cut stone and is referenced in the International Building Code under Chapter 14, Anchored Masonry Veneer.

The earliest known use dates to about the year 1138 and can still be seen at Carcassonne, France, a city that contains some of the finest remains of early architecture in Europe. Cast stone was first used extensively in London beginning around 1900 and has gained widespread acceptance in America since the 1920s. According to Gary Fry, President of Board of Directors of the Cast Stone Institute, “Many lessons have been learned throughout this history and they can be used to improve the mason contractor’s experience with cast stone at the current state of the art.” The requirements for Cast Stone are referenced in the current ASTM International C1364 Standard for Architectural Cast Stone which was originally approved in 1997 and most recently updated in 2007, although various trade groups had published specifications as early as 1927.

Cast stone is generally built into a load bearing masonry wall system, and used as an architectural feature, trim, ornament or veneer in traditional commercial and residential buildings and other structures. It is most often specified as a replacement for full bed-depth natural dressed dimensional limestone.

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. It is sometimes referred to as Simulated Stone or adhered veneer. AMSMV is generally applied as a residential or lightweight commercial masonry veneer adhered to exterior and interior walls, structures, columns, landscape structures, and other structures suitable to receive lightweight adhered units. It is known by a variety of different product names with a variety of proprietary specifications. Several companies manufacture stone-like products that are used primarily as veneers on other substrate materials such as concrete masonry units. These simulated stone products are manufactured to meet Construction Specifications Institute (CSI) Division 047300 classification for simulated stone while cast stone is manufactured to meet Division 047200 requirements. There are currently no ASTM standard specifications for AMSMV. top

PHYSICAL PROPERTIES
There are substantial differences between cast stone and adhered veneer in regard to physical properties that should be considered when specifying. Adhered veneer is a lightweight product that is applied to a structural wall with an adhesive. Therefore, it cannot be used to add to the load bearing capacity of the wall. Cast stone, however, can be used to add to the load bearing capacity of a masonry wall and is usually integrated into the brickwork, becoming part of a composite wall system rather than being adhered to it. It provides additional strength because it is anchored within the masonry structure, therefore will stand the test of time. In addition, while adhered stone products are made light in weight so they will work easily on the exterior of other wall material, cast stone weighs approximately the same as natural cut limestone.

Test methods dictate how the materials are tested while the specification stipulates what the requirements of the test results must be, as well as the ingredients each product must contain.

For example, cast stone is required to have a minimum compressive strength of 6,500 psi, maximum moisture absorption of 6 percent, and unit density of approximately 135 pcf. The minimum compressive strength of adhered veneer is approximately 1,800 to 2,000 psi, absorption may reach 22% (UBC Standard 15-5), unit density is approximately 75 pcf, and much emphasis is put onto a shear bond test which is presently under development. Each product must pass a rigorous freeze-thaw test. Because AMSMV is an adhered unit, most building codes such as UBC/IBC require the maximum density to be 15 lbs per square foot, and allow the minimum thickness to be approximately ¼”. Cast stone when used in conventional 3-5/8” thickness weighs approximately 40 psf.

APPEARANCE
The use of a high percentage of durable fine aggregate in any manmade stone creates a very smooth, consistent texture for the building elements being cast, resembling natural limestone, brownstone, sandstone, marble or granite. Applications that use cast stone can range from the simplest window sill to the most complicated classical architecture. Therefore, the number of profiles and sizes required for any given project can vary from a single shape shown on a sketch to hundreds (or more) shapes, perhaps not so clearly shown in a set of architectural contract documents.

AMSMV usually has a natural quarried stone appearance and can be used for many of the same applications, although it is primarily used as adhered veneer. Both products have many of the same properties inherent in a material which is primarily intended to simulate natural building stone, although cast stone is typically custom made to approved shop drawings and AMSMV is most often laid out and cut to suit field conditions.

INSTALLATION
Cast Stone is generally used as the veneer or trim component of a conventional masonry cavity wall system, similar to brick veneer. Therefore, concrete masonry units (CMU), steel frame, concrete or metal studs are typically built out from a backup wall with a 1” to 4” air space, which may include insulation. Sizes of cast stone are typically made to accommodate pallet lengths of 4’ to 5’ and are commercially available in sizes up to 24 sf in area. Larger sizes are still possible, subject to local availability, but may not be recommended for use in mortar set systems.
A typical masonry cavity wall has five essential elements. top

• Exterior wythe of masonry
   

• A clear cavity, or air space, of at least 1 inch
   
• An interior wythe of masonry or other backing material
   
• Flashing at all interruptions in the drainage cavity
   
• Weep holes at all flashing locations. Recommended spacing of 24 in. o.c.

The exterior wythe provides first resistance against moisture penetration. Cast Stone should be laid with full joints in mortar meeting the requirements of ASTM C 270, Type N mortar. Care should be taken when laying the stone to ensure the cavity behind this wythe stays clear. A tapered bed joint can help minimize mortar droppings and protrusions into the drainage cavity. Stainless steel building stone anchors are used to tie the cast stone to the backup wall. They are designed to be stiff enough to resist tension and compression, and flexible enough to permit in-plane differential movements. Non-corrosive type anchors should be used for all anchoring. Stainless steel Type 302 or 304 are the standard type used in this class of work.

Typical stone anchor sizes are 1/8" x 1" straps, 1/4" rods and 1/2" dowels. Dowel holes for 1/2" or 3/4" dowels are usually 1" diameter filled completely with mortar during setting. Anchor slots are typically 3/4" wide and similarly are filled with mortar.

The anchors for attaching cast stone may be required to penetrate flashing and building paper to allow a secure connection to the structure. Where this occurs, proper steps must be taken to ensure a watertight connection at the interface so that the anchor does not compromise the integrity of the flashing.

Alternative Cast Stone Thin Veneer Installation Methods
Over the past twenty years alternative thin veneer methods have been successfully installed and accepted within the masonry industry and most recently have been designed for thin veneer cast stone. These new methods of installation using corrosive protective steel as a support panel to anchor the steel panels in place have incorporated specially designed tabs to assist in holding the weight of each masonry unit without the use of hung lintels or relieving angles, some even offer a mortar locking feature to mechanically lock the mortar & thin veneer onto the steel support panel. These systems are designed to match the different types of expansion and contraction between the veneer, panel, and substrate. They offer greater fastener pull through resistance than cement board, polystyrene, plywood, OSB and asphalt board. Some of these systems even offer a true moisture control system, which allows the water to drain. Depending on the type of system used, structural steel support panel systems will successfully hold thin masonry cast stone veneer up to 150 MPH wind-loads at 400’ high, per exposure D (ASTM-E-72). top

Figure 5 (Courtesy TABS Wall Systems)

Regardless of the material selected and the degree of care exercised during construction, a final wash down will be needed after installation and, normally, whatever is specified to clean the masonry will adequately clean the stone. A variety of commercial cleaners are available and most contain detergents combined with mild solutions of phosphoric and/or muriatic acids. Extreme care should be taken when applying acidic cleaners to areas where joints are left open or where sealant is used as jointing material. As with any cleaning solution, always consult with the stone manufacturer and try a test area first, before proceeding with the wash down. The window and sealant manufacturer should also be contacted to ascertain compatibility with cleaning materials.

AMSMV is an aesthetic wall covering, but it is the structural backup behind the adhered veneer that does all the work in resisting loads. The backup wall may be wood framing, sheet metal, steel framing, concrete block, or poured in place concrete. With adhered applications, the stone veneer will move with the backup wall as the structure responds to loads, temperature variations, and soil settlement. AMSMV veneer is relatively stiff, and is well-matched to a concrete block or poured in place concrete backup system. Wood and steel framing, on the other hand, are relatively flexible. Choosing a stiff backup structure (L/600 to L/1,000) is required to prevent future cracking of the adhered veneer. Wood framing is particularly susceptible to movement as the wood swells during damp periods, and shrinks when it dries.

AMSMV may be set using one of the following International Building Code methods, in lieu of another approved method, after properly installing a metal lathe to the substrate:

Back-butter and squeeze - Brush a paste of neat Portland cement on the backing and on the back of the veneer unit. Then apply Type S mortar to the backing and to the veneer unit. Sufficient mortar shall be used to create a slight excess to be forced out the edges of the units. The stones shall be tapped into place so as to completely fill the space between the stones and the backing. The resulting thickness of mortar in back of the units shall not be less than 1/2" or more than 1-1/4". Grout and finish joints as necessary. top

1. 1. Back-butter and squeeze - Brush a paste of neat Portland cement on the backing and on the back of the veneer unit. Then apply Type S mortar to the backing and to the veneer unit. Sufficient mortar shall be used to create a slight excess to be forced out the edges of the units. The stones shall be tapped into place so as to completely fill the space between the stones and the backing. The resulting thickness of mortar in back of the units shall not be less than 1/2" or more than 1-1/4". Grout and finish joints as necessary.
    
2. 2. Mortar setting bed - The setting bed of mortar shall be a minimum of 3/8" thick and a maximum of 3/4" thick. A paste of neat Portland cement or one half Portland cement and one half graded sand shall be applied to the back of the exterior veneer units and to the setting bed, and the veneer shall be pressed and tapped into place to provide complete coverage between the mortar bed and veneer stone. Grout and finish joints as necessary.
    
3. 3. Use a combination of the two methods listed above.

Adhesion developed between adhered veneer units and backing shall have shear strength of at least 50 psi based on gross unit surface area. For veneer units weighing less than 3 pounds per square foot, there is no limit on its dimensions or area. Veneer units may not weigh more than 15 pounds per square foot. For veneer units between 3 and 15 pounds per square foot, the following dimension and area restrictions apply. No side of the veneer units can exceed 36 inches in length and the overall face area of the stone may not be greater than 5 square feet.

SPECIFICATION OF PRODUCTS
In November 2006, ASTM International Committee C15 on Manufactured Masonry Units created a new subcommittee, C15.11 on Adhered Manufactured Stone Masonry Veneer. The purpose of C15.11 is to develop and maintain product specifications and installation guidelines for adhered manufactured stone masonry veneer. The new standard was still under development at the time this article was written.

ASTM International (founded in 1898 as the American Chapter of the International Association for Testing and Materials and most recently known as the American Society for Testing and Materials) exceeds 30,000 technical experts from more than 100 countries who comprise a worldwide standards forum. The ASTM method of developing standards has been based on consensus of both users and producers of all kinds of materials. The ASTM process ensures that interested individuals and organizations representing industry, academia, consumers, and governments alike, all have an equal vote in determining a standard's content.

According to Brenda Harris, chair of the new subcommittee, adhered manufactured stone masonry veneer has recently been defined by Committee C15’s executive subcommittee as “a light- weight architectural non-load bearing product. It is a wet cast blend of cementitious materials, lightweight and other aggregates, iron oxide pigments and admixtures.”

Harris says that the subcommittee was formed because there are not currently any well-known standards for adhered manufactured stone masonry veneer. “The lack of a uniform and nationally recognized product standard and the lack of specific and appropriate installation procedures for this product have allowed untested and substandard products to find their way into both residential and commercial construction,” says Harris. “The development of these standards would create the critical definitions and procedures needed by project owners, as well as design and installation professionals.”

Considering the many advantages which man made stone has over natural building stone, it is surprising that wider use has not been made of this versatile and economical building material. Many architects are only now discovering Cast Stone. Although it has existed for more than centuries, the merits of it as a versatile ornamental building material are still far from universally recognized.

For thousands of years, architects and builders have chosen stone as an architectural medium - for its beauty -- for its permanence. So, what will man do when the last natural stone is quarried?

He will make his own.

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Author: Bill Russell is the Chairman of ASTM Committee C 27.20 on architectural and structural concrete products, and President of Continental Cast Stone East, by Russell, Inc., Berlin, NJ. He is a founder and past president of the Cast Stone Institute, served as its Technical Director for 14 years and presently chairs its Committee on Educational Standards.


 

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