RepairQ I have a client with an old, soft-stone masonry building of approximately 150 years of age. The mortar is badly deteriorated and the stone is quite friable. I am advocating the use of shotcrete as an application to the interior face of the walls that will restore both in-plane and out-of-plane strength to the building walls. My client has expressed concern that there may be incompatibility issues between the stone masonry and the shotcrete both from a structural stiffness perspective as well as from a moisture intrusion perspective. (We have successfully used shotcrete over stone masonry in the past.) Do you have any information you can share with me on this topic? Do you have either examples of incompatibility or successful use of shotcrete over stone masonry?
As you have noted, shotcrete has been used extensively to reinforce unreinforced or under-reinforced masonry walls and rock walls. It has been used on the Crater Lake Lodge to strengthen and stabilize a rock wall foundation and any number of other projects. In California, shotcrete has been used to strengthen or repair walls since the 1933 Long Beach Earthquake. It was used to strengthen the California State Capitol (3 ft [0.9 m] thick brick walls) in the late 1970s and all of the older unreinforced masonry walls for the San Francisco School District. To the best of our knowledge, there have been no failures of shotcrete strengthening on the West Coast in the past 80 years.
