Can you put new varnish over old varnish?
Likewise, can I varnish over varnish 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.
Beside above, can I put polyurethane varnish over Spar varnish? Spars have a greater oil ratio than an interior varnish or oil base polyurethane. Coating over it with either of those would maintain that softness/flexibility as a base coat. High End spar varnishes ( I wouldn't use these indoors) tend to take much longer to dry and stay much more flexible than spar urethane.
Similarly, you may ask, can you varnish over existing varnish?
It is possible to apply stain over varnish, as long as you aren't expecting results similar to those when staining untreated wood that drinks in the stain. Clean and rough-up the varnish first to remove any grime, dust or debris and also to give the surface some texture the stain can cling to.
How do I remove varnish?
You can use a stiff-bristled scrub brush to remove varnish from fancy, curved details. Some of the stain may linger after scraping. To remove it, dampen a soft, fine-grade steel-wool pad with more paint stripper and rub it against the wood, following the wood grain, then wipe off the softened stain with a rag.