Can you whitewash over varnish?
Also, can you paint over varnished wood without sanding?
Painting Over Varnish Without Sanding. It is often recommend that you sand any surface thoroughly prior to painting it. Painting over varnish without sanding is not a best practice but it can be done.
Keeping this in view, can you whitewash over lacquer?
The answer is no, you cannot whitewash over a pre-existing finish as the original stain or finish will create a barrier, and the whitewash will not be able to penetrate to the wood. You can, however, use solid stain over old panelling and it looks terrific.
A polyurethane will add a yellow tint to your piece, which is fine when staining wood, but not suitable for a whitewash effect. And the satin finish is much more natural looking than a high gloss.