What is the difference between Cast Stone and architectural precast concrete?
The short answer is that Cast Stone is used in place of natural stone. As a type of building stone, Cast Stone is specified under the masonry division 04720. It is usually set by a masonry contractor using standard building stone anchors. Perhaps most important, unless otherwise specified, Cast Stone looks like natural, dimensional, cut building stone. Upon close examination, the finish of Cast Stone looks like limestone; some call it a “sugar cube finish” to distinguish its appearance from the “pebbly with voids” appearance which is normally associated with concrete. This dense finish is more resistant to weather and dirt; and the fine aggregates retain the granular, texture through decades of exposure to the elements. Sandblast or chemical retardation finishing methods (normally used in finishing of architectural precast concrete panels) are seldom used with Cast Stone because of the dulling of aggregates and the loss of fine detail which are not acceptable in quality Cast Stone work.
What is efflorescence and why does it occur?
Efflorescence is a calcium or alkaline salt which forms as a blotchy, powdery or crystalline deposit on the surface of masonry walls and concrete products. It is due to moisture entering through the walls or the surface of the Cast Stone, combining with the calcium hydroxide in the cement, and bringing the hydroxide to the surface in a solution which forms crystals when it combines with the carbon dioxide in the air. For more information please refer to Cast Stone Institute Technical Bulletin # 33.
What is crazing and why does it occur?
Crazing is defined as fine and random cracking extending only through the surface. Crazing is due to differential contraction between the surface and interior sections. Crazing can be caused by any factor which causes surface tension in excess of interior tension. Manufacturing causes include inadequate or improper curing, a surface film richer in cement and fines than the body of the concrete and plastic shrinkage cracking. Crazing can also be caused by design and installation factors which cause unusually high amounts of vapor transmission, excessive wetting and drying or inadequate ventilation behind the Cast Stone. There is some evidence that atmospheric carbonization can cause crazing. Crazing has no structural or durability significance For more information please refer to Cast Stone Institute Technical Bulletin # 32.
What are the recommended cleaning procedures for Cast Stone?
Regardless of the degree of care exercised during construction, a final wash down will be needed and, normally, whatever is specified to clean the brickwork will adequately clean the Cast Stone. Varieties of commercial cleaners are available and most contain detergents combined with mile 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. The sealant manufacturer should be contacted to ascertain compatibility with cleaning materials. Acids left behind the stone on masonry wythe may cause corrosion problems later on.The most common stains due to construction are dirt and mortar. Dirt can be removed by scrubbing with a mild detergent and water. Mortar stains require brushing a solution of one part hydrochloric acid to six parts water on the stain. Soak the stone with water prior to adding any acid solution to prevent surface burning. Consult the brick supplier prior to applying acids to trim items. Insure that lower stone courses are frequently drenched with water because as acid is rinsed down the wall it can gather strength when reapplied. Take necessary steps to protect windows, door, and grade materials. For more information please refer to Cast Stone Institute Technical Bulletin # 39.
Should we point the joints or use a flexible sealant?
The decision on whether to use mortar with pointed joints or sealant joints between stones is a common one. All head joints at coping stones and joints at column covers, cornices, platforms, soffits, window sills and in general, all stone sections with projecting profiles, exposed top joints or rigid suspension connections to the supporting structure should be “soft” sealant joints.Mortar joints are best suited for masonry-bound trim items such as belt courses, lintels, window surrounds, date stones, inscription blocks, quoins, keystones and similar applications. Always rake and point mortar joints rather than full-bed setting and finishing in one operation. See Technical Bulletin #44 on Pointing. Not all Mortars are created equal. Selection of the correct grade of mortar is perhaps the most important factor in the performance of a masonry wall. The mortar must have sufficient strength, be durable, resist rain penetration as much as possible and yet be flexible enough to accommodate slight movement within the wall. See Technical Bulletin #42 on Mortars. Not all joints between stones or between stone and other material should be filled with mortar. All head joints at coping stones and joints at column covers, cornices, platforms, soffits, window sills and in general, all stone sections with projecting profiles, exposed top joints or rigid suspension connections to the supporting structure should be “soft” sealant joints. See Technical Bulletin #43 on Sealants.
How do we patch Cast Stone?
Patching Cast Stone is done by the Setter. A Patch Kit is available from Corinthian Cast Stone Inc. for your project. For more information please click onto the Patching Instructions page or the Cast Stone Institutes Technical Bulletin # 38.
Are there special considerations when setting Cast Stone in Hot or Cold Weather?
Both hot and cold weather present their own set of challenges while setting Cast Stone. In hot weather care should be taken to soak the Cast Stone prior to setting and to be sure the mortar has and retains sufficient water to ensure a proper bond to the Cast Stone. The increased rate of hydration of the cement and favorable curing conditions in hot, humid weather will help develop masonry strength provided sufficient water is present at the time of construction and for a curing period of three days. In cold weather care should be take to follow the recommendations set forth by the International Masonry Industry All Weather Council. Further information can be found in the Cast Stone Institute Technical Bulletins # 41 (Cold Weather Setting Practices) and # 48 (Hot Weather Setting Practices).
What do we need to know about Flashing and Weep Holes?
Proper flashing and weep holes are essential elements in exterior masonry walls. Together, they provide a means to control moisture in a wall. If not addressed, moisture can have damaging effects on exterior walls. Excessive moisture within masonry can lead to crazing, efflorescence and spalling in some cases. Improper flashing can lead to moisture in the interior of a building. An effective system to deal with exterior moisture penetration is necessary for a properly functioning Cast Stone wall. For more information please refer to Cast Stone Institute Technical Bulletin # 39.
What are the guidelines for Inspection and Acceptance of Cast Stone?
On site inspection and acceptance of Cast Stone should be performed at time of delivery and again after all material has been installed, pointed and cleaned. Final Inspection should be done prior to application of water repellents. The on site inspector should be familiar with the project specification as well as the applicable referenced standards. Test reports of compressive strength, absorption and other physical properties should be on file as well as the approved sample. For more information please refer to Cast Stone Institute Technical Bulletin # 36.Please Take Notice, Corinthian Cast Stone Inc. requires our customers to Sign and Print the receivers name as well as the company’s name when accepting a shipment. All discrepancies must be noted and forwarded in writing to Corinthian Cast Stone Inc. with in 24 Hours of Delivery.
What should site personnel be aware of regarding Job Site Handling and Installation?
The on-site personnel should be familiar with the applicable sections of the Cast Stone Institute Specifications and the Project Specification pertaining to delivery, storage, setting, patching, cleaning, pointing, caulking and sealing. In case of a conflict between the two specifications, the Project Specification should prevail. Where the Project Specification may not include a particular issue, the Industry Standards should be followed. To review a comprehensive checklist please see the Cast Stone Institute Technical Bulletin # 37./expand] Why doesn't VDT Cast Stone need Air Entrainment Additives?In many project specifications today, air entrainment is specified for Cast Stone mixtures when it is only required for units manufactured from wet-cast slump concrete. It is not necessary to add air entrainment additives to units manufactured from zero slump mixes. Accordingly, ASTM C 1364-02 Standard Specification for Architectural Cast Stone only requires mixtures to contain air entrainment additives for units manufactured from slump concrete mixes. For more information please refer to Cast Stone Institute Technical Bulletin # 50.
Should we apply a Water Repellant?
The technology of waterproofing masonry materials has improved considerably in the last few years and many durable water repellent materials are available which can reduce water intrusion through brick, stone and mortar joints. Proper application of waterproofing materials can be a long lasting minimizer of efflorescence, mildew, staining and dirt. Many materials are offered with 5-10 year warranties. Some studies indicate that water repellents can reduce freeze-thaw damage to masonry products and prevent loss of insulation value.The most popular and time-tested water repellents include silicones, acrylics, silanes and siloxanes. Silicones are relatively inexpensive, only provide a surface film, and usually, only last a short time. Silicones are mainly used to keep Cast Stone clean during construction operations and they make the finished installation easy to clean. Many types of acrylics are available but most have poor vapor transmission, low penetration and inadequate resistance to ultraviolet light. Some acrylics have been known to turn yellow or produce gloss. The Cast Stone Institute recommends the use of silane or siloxane (or blends containing each) for weatherproofing Cast Stone when a water repellent is desired. For more information please refer to Cast Stone Institute Technical Bulletin # 50. Corinthian Cast Stone Inc. recommends following the water repellant manufactures written instructions and additionally testing the sealer in a small inconspicuous area prior to general application.
What Colors can you manufacture and how long does it take to get a color sample. Is there a charge for Custom Color matching?
Corinthian Cast Stone Inc. offers lines of Standard Colors and Premium Colors as well as Custom Colors.Standard Colors are made from our primary base aggregate, white or grey Portland cement and select iron oxide pigments. Any of these Standard Colors are included in Cast Stone Proposal you have received from your Project Coordinator.Premium Colors can be made from either our primary base aggregate, a specialty aggregate or a combination of multiple aggregates, either white or grey cement and iron oxide pigments. There is an additional charge for these colors. Custom Colors are made to order. A sample of the material you desire to have Corinthian Cast Stone match is sent along with a Color Match Form and a Color Match Fee. CCS will then provide you with a range of up to five samples to select from. Custom Colors are made from a multitude of aggregates, white or grey cement and select iron oxide pigments. If you select Standard or Premium Colors, a sample of the closest match we have will be sent the same day we receive your Color Match Form and the sample you wish us to match. If you select to have a Custom Color for your project, we will send you samples usually within two weeks from receiving you sample, Color Match Form and the Color Match Fee. Upon receiving the sample you desire to match, you will be informed if a specialty aggregate is needed to match your color and of the additional cost associated with that aggregate. Custom Color match sample size sent to you will be approximately 6″x 6″x 1″.
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