We are considering the use of shotcrete to repair a building wall that has been badly spalled. Assuming that all unsound material has been removed and the surface properly cleaned, will it be necessary to use a portland cement grout or an epoxy as a bonding agent? Should steel be attached to the wall before shotcreting?
No bonding agents are necessary for shotcrete. The bond of shotcrete to old surfaces is satisfactory if the surface is properly prepared. Unless bonding or shear stresses are acting on the wall surface no mesh is required. However, as an added safety feature mesh can be used in any shotcrete that is over one and one-half inches in thickness. The mesh should be furred out or attached to the surface with powder activated studs. It is desirable that the mesh be no closer to the exposed surface than the middle of the shotcrete thickness and have a minimum of one-inch cover.