Live in Illinois have concrete foundation from 1950s. Have concrete spalling below brick line about 8 to 12 inches below ground level. Dug out trench about 18 inches scraped off loose crumbling cement some areas were deep about 3/4 inches deep wired brushed power washed and patched with pantitop xs martar. Left trench open over winter recently went to inspect work and found some areas popped or loosened up. Upon checking i tapped it sounded hollow and some came off. The adhesion was good the issue was the spall problem went deeper. I redug deeper removed loose patching again. I don't know if I should use a bonding agent to repatch the area. One thing I did on the initial patch job was parch the area with a scrub coat I let it dry for an hour before applying repair mortar. I am at a loss here on how to stop the spalling from getting worse. I wanted to repatch area again and seal with a rubber type Grey shield for foundations. I think moisture is getting under the patch work possibly. Gutters drain away from house and grade is pitched properly.