Both varnish and polyurethane protect wood, but they’re not the same thing. Understanding the differences helps you choose the right finish for your project.
What’s Varnish
Traditional varnish is oil and resin cooked together, thinned with solvent. Spar varnish (marine varnish) stays flexible for outdoor use. It’s been around for centuries and still works well.
Varnish builds slowly, requires more coats, and takes longer to dry. But it penetrates into the wood and creates a warm, deep finish.
What’s Polyurethane
Polyurethane is a synthetic resin – technically a type of varnish but with different properties. It’s harder, more water-resistant, and dries faster than traditional varnish.
Oil-based poly adds warmth (amber tint). Water-based poly stays clear and dries very fast but can raise grain.
When to Use Varnish
Exterior applications – spar varnish handles UV and weather better. Fine furniture where you want a hand-rubbed look. When you’re willing to spend more time for a traditional finish.
When to Use Polyurethane
Kitchen tables, floors, anything that needs maximum durability. Projects where you want multiple coats in a day. When you need water resistance indoors.
Application
Both apply similarly – thin coats, sand between coats, multiple layers. Polyurethane is less forgiving of brush marks. Wipe-on versions of both are easier for beginners.
My Preference
I use oil-based poly for most indoor furniture – durable, easy, adds warmth. For outdoor projects, spar varnish performs better. For pieces where I want a softer look, I skip both and use oil or wax.
There’s no wrong answer. The best finish is the one that protects the piece and gives you the look you want.
