When painting a previously varnished internal or external surface, a successful outcome will depend on effective preparation and correct choice of prime. There are many products available which are designed for this purpose, Dulux Super Grip, Zinsser Bulls Eye 123 Plus and Zinsser BIN to name but a few. I use all these products on a variety of internal and external varnished surfaces ranging from doors, panelling, cladding and melamine and they have never yet failed to adhere to the surface. However, I would always use Zinsser BIN on exterior surfaces because of its enhanced stain killing qualities and quick drying time.
All these primes can accommodate the application of all of both waterborne acrylics and solvent paint systems.
To improve the adhesion of the primer to the varnish surface it is very important the surface that is to be painted is properly rubbed down, and all loose and defective decorative layers are removed, dust off debris and wash off any dirt, oil or grease with either white spirit, a decorative cleaning agent such as Sugar Soap or Zinsser Universal Degreaser Cleaner and allowed to fully dry before proceeding with the primer.
Once the surface is primed and fully dry you are free to apply the finishing paint system of your choice, do please consider using a modern eco-