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2015WinterShotcreteEMag

Shotcrete FAQs experience with this issue and is there a way to shotcrete both material. It is reported that this was troweled on approximately the wall and the column? 20 years ago. We have made test holes and it is adhered very well, except Answer: There have been many prior projects in the city of where moisture penetration through the parapet has compro- Los Angeles where columns and pilasters are incorporated into mised adhesion. This is installed with five layers approximately perimeter basement walls. This would likely require a precon- 1 in. (25 mm) thick. We are considering leaving the material struction mockup panel and might require a waiver from the in place, patching as required, and removing the existing non- City Engineering Department. It is extremely important to permeable paints (which are peeling). Our thought is to coat ensure that the work is done by a qualified and experienced the surface with a variegated colored stain, allowing for per- shotcrete specialty contractor who has documented experience meability of vapor. doing similar work. Can the material be patched as necessary? What is the recommended finish? Do we need to be concerned that the Question: Can Pozzutec 20+ (or any other accelerating material could permit water penetration? Are there certified admixture) be used with a dry-mix shotcrete? If so, has it been contractors in the Cleveland, OH, area? used on any large-scale projects? Answer: From what you have described, the original work Answer: Pozzutec 20+ is intended for use in ready mixed may have been done by the shotcrete process or hand-applied. concrete. Although it may work with dry-mix shotcrete, there Typically in the shotcrete process, over a large area at the thick- are other products that are designed for use in the wet and dry ness of 5 in. (127 mm), you would expect to see reinforcing shotcrete processes. mesh or reinforcing bars. The material can be patched. If the areas are small, it may Question: We are looking at constructing climbing boulders be prudent to hand patch. Shotcrete is most effective in larger made with shotcrete and using a polystyrene core. Does the applications. It is important to select a good repair mortar or polystyrene need to be covered with a protective membrane to mixture design. protect it during the spraying process? Also, could the poly- ASA does not have a recommended finish. Generally in this styrene contribute to the structural integrity of the boulders, type of application, the goal would be to match the existing or should it just be used as a void-forming material? surfaces as close as reasonably possible. Many patches are done on bridges and other structures Answer: Polystyrene is available in various densities and the without regard to water penetration. denser the product, the less likely that the shotcrete process We do not have certified contractors; however, many of our will cause any damage to it. The question of the structural value corporate contractor members have ACI Certified Nozzlemen of the polystyrene needs to be addressed by a competent struc- on their teams and the Buyers Guide on the ASA website can be tural engineer. It is not something that we, as a shotcrete asso- searched by location and specialty. Also on our website, we have ciation, feel qualified to comment on. a position paper on “Shotcrete Contractor and Crew Qualifica- tions” with a handy checklist summary that would be useful in Question: I am an architect working on a project in which a qualifying potential contractors for your project (www.shotcrete. masonry building was “coated” with a shotcrete or gunite org/media/Archive/2014Win_ShotcreteCorner.pdf). BECOME AN AUTHOR FOR Upcoming Themes: SUMMER 2015 FALL 2015 Pools Equipment …as well as Shotcrete Corner, Technical Tip, and more. For more information, contact the ASA offices at: American Shotcrete Association • 38800 Country Club Dr. • Farmington Hills, MI 48331 Phone: 248-848-3780 • Fax: 248-848-3740 E-mail: info@shotcrete.org • Website: www.shotcrete.org Shotcrete • Winter 2015 63


2015WinterShotcreteEMag
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