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ArchitecturalQ We are working with an architect in New York City on an unreinforced masonry (URM) building where they want to remove brick to provide a larger storefront opening. I would like to use the remaining walls to resist lateral forces but the brick is insufficient. We would like to remove one width of brick and apply 4 in. (102 mm) of reinforced shotcrete in its place. Can you tell me where I can find applicable code and design guidelines for this application?
Your proposed solution is certainly reasonable and is used regularly. Shotcrete has been used to strengthen both URM and tilt-up panels to accommodate enlarged openings. Shotcrete is a method of placing concrete and the in-place properties would be the same. The applicable code would be the code you would use if you were to strengthen this wall with concrete. Designs using the ACI 318 Building Code and Commentary are fully applicable to shotcrete placement, although compressive tests for acceptance are secured using cores from shotcrete test panels per ASTM C1140/C1140M and C1604/C1604M, rather than cast cylinders.
ArchitecturalQ We recently stained a shotcrete wall. After we placed the staining on the wall, the stain came out in different shades across the wall, in effect bring out the different curing of the concrete. What can be done to eliminate this inconsistency?
It is not unusual to have variations in the tone of color for shotcrete or concrete walls that have been stained due to variation of the texture or density of the surface being stained. An acid-based stain typically results in more consistent shading. When anticipating that a wall will be stained, extra care needs to be taken in the curing process. It is generally recommended that walls to be stained should be water-cured to avoid any interaction between a curing compound and the stain material. If a curing compound is used, it must be completely removed prior to applying the stain material. Consult the stain supplier for more information.