Frenchic Sugar Soap is specially formulated to clean and prepare all surfaces prior to painting.
Add approximately 1 part sugar soap to 4 parts warm water. Apply liberally using a sponge or absorbent cloth. Work from the bottom of the surface to the top to avoid run lines. Rinse with fresh water and allow to dry completely.
It's also brilliant for household cleaning: Add approximately 1 part sugar soap to 10 parts warm water. Soak sponge or absorbent cloth in the solution and wring out so it does not drip. Wipe surface vigorously. Rinse with clean cold water.