New dark marble dust not adhereing to old surface.

[Stan]

Last year my gunnite pool was renovated. Copings repaired, new tile and dark grey marble dust. In a short time 2 large pieces of the new marbledust separated. At the end of the summer, the pool was drained and a repair was made. Now there are other areas that are separating. The repair looks like patches. What causes this separation? I want the company to do the entire pool over. How can the same problem be avoided.