To prepare oil-based paint for water-based paint, you must apply a coat of sealer first. This provides a suitable base for the water-based paint to adhere to. You can then use an undercoat before applying the final gloss coat.
Essentially, the process involves creating a barrier layer that allows the water-based paint to properly bond to the underlying oil-based paint. Without this, the water-based paint may not adhere correctly and could peel or flake.
