Can I use General Finishes Milk Paint over an existing finish that is chipping?

If your current finish is chipping, it is failing to adhere correctly. The adhesion problem could be caused by several reasons:

1. Improper preparation: Cleaning an existing finish removes dirt, grime and many common contaminants such as oil from hands. Dirt, grime and oil prevent good ahesion causing the possiblility of chipping, peeling and flaking - all signs of a failed finish.
2. Contaminants from dusting sprays that contain silicone will also impact the appearance and adherence of a finish - silicone is almost impossible to remove. Oil soaps and wax can also cause ahesion failures.
3. The previous paint was a "chippy style" paint, such as an original casein based milk paint that does not contain the necessary resins for high durability

We would not recommend applying any of our products over a failing finish, because the underlying finish could continue to present adhesion problems. Your only recourse for a good result is to remove the current finish by stripping and sanding.