A concrete foundation should be prepared for grout by removing all laitance with a chipping hamper with a chisel bit.
Remove all laitance with a chipping hammer.
Make sure the concrete is properly hydrated.
Be sure the concrete is free of any oil or contaminants.
It is unacceptable to sand blast a foundation in preparation for grout. Preparation will need to be done with chipping hammers. A chipping hammer will properly profile the foundation and remove the laitance layer.