ArchitecturalQ I am an architect working on a project in which a masonry building was “coated” with a shotcrete or gunite material. It is reported that this was troweled on approximately 20 years ago. We have made test holes and it is adhered very well, except where moisture penetration through the parapet has compromised adhesion. This is installed with five layers approximately 1 in. (25 mm) thick. We are considering leaving the material in place, patching as required, and removing the existing nonpermeable paints (which are peeling). Our thought is to coat the surface with a variegated colored stain, allowing for permeability of vapor. Can the material be patched as necessary? What is the recommended finish? Do we need to be concerned that the material could permit water penetration? Are there certified contractors in the Cleveland, OH, area?
From what you have described, the original work may have been done by the shotcrete process or hand-applied. Typically in the shotcrete process, over a large area at the thickness of 5 in. (127 mm), you would expect to see reinforcing mesh or reinforcing bars.
The material can be patched. If the areas are small, it may be prudent to hand patch. Shotcrete is most effective in larger applications. It is important to select a good repair mortar or mixture design.
ASA does not have a recommended finish. Generally in this type of application, the goal would be to match the existing surfaces as close as reasonably possible.
Many patches are done on bridges and other structures without regard to water penetration.
We do not have certified contractors; however, many of our corporate contractor members have ACI Certified Nozzlemen on their teams and the Buyers Guide on the ASA website can be searched by location and specialty. Also on our website, we have a position paper on “Shotcrete Contractor and Crew Qualifications” with a handy checklist summary that would be useful in qualifying potential contractors for your project.
