Varnish vs Polyurethane: A Decision I Make Wrong Constantly

I have been woodworking for over 20 years and I still reach for the wrong can sometimes. Varnish when I should have used poly, poly when varnish would have been better. They are both clear-ish wood finishes, they both come in cans, and the hardware store puts them on the same shelf. The confusion is practically engineered.

Let me try to sort this out, mostly so I can refer back to this article next time I am standing in the finish aisle at Lowes looking confused.

The Basic Difference

Varnish is the old-school finish. Oil-based resin plus drying oils, mixed to make a protective film. It is what shipbuilders and furniture makers used before plastics existed. There are different types – spar varnish for outdoor stuff, marine varnish, long-oil and short-oil formulations – but they all share that oil-resin base.

Polyurethane is essentially plastic dissolved in solvent. It dries harder than varnish and is more resistant to scratches and chemicals. Oil-based poly has been around since the 60s; water-based poly is newer but increasingly popular because it dries faster and does not yellow.

So: varnish is classic, poly is modern. That is an oversimplification, but it is a starting point.

Where Varnish Wins

Outdoors. This is where varnish shines (literally). Spar varnish stays flexible as temperature changes, expanding and contracting with the wood. Polyurethane tends to crack and peel in those conditions because it forms a more rigid film.

I have got an Adirondack chair finished with spar varnish that has been on my deck for six years. It needs a fresh coat every year or two, but the finish is still intact. Compare that to a planter box I did with exterior poly – the finish was peeling after two seasons. Total pain to strip and refinish.

Varnish also has a warmer look. It enhances wood tones without making them plasticky. On antique restoration or when I want that hand-rubbed traditional appearance, varnish is still the right call.

Where Poly Wins

Hard use. Table tops, floors, kitchen cabinets, desks – anywhere stuff gets dragged across the surface, set down hard, or exposed to food and drink. Polyurethane is just tougher.

I finished my shop bench top with oil-based poly seven years ago. This bench gets hammered on daily – literally. Glue spills, chisel marks, stuff dropped on it constantly. The finish is beat up but still protecting the wood. Varnish would have worn through years ago.

Water-based poly is especially good for light-colored woods. Maple, ash, white oak – anything where you do not want that amber cast that oil-based finishes add. I did a maple nightstand with water-based poly and the wood stayed pale and clean. Would have looked orangish with oil-based.

Drying Time (Why This Actually Matters)

Varnish takes forever. Like, forever. 24 hours between coats is the minimum; 48 is safer. Three coats means a week of your life for a simple project. And if you do not wait long enough? The new coat wrinkles or will not bond properly.

Oil-based poly is similar – 24 hours between coats, longer in humid weather.

Water-based poly dries in 2-4 hours. You can do three coats in a single day. This is a huge deal when you are trying to finish a project before the weekend ends or a client deadline approaches.

Of course, faster drying means less time to brush it out, so water-based can show brush strokes if you are not careful. Trade-offs everywhere.

Application Quirks

Varnish is surprisingly forgiving. It is thick, flows well, and you have time to work it before it sets up. Perfect for someone who is not a finishing expert (like me, honestly). Brush marks level out as it slowly dries.

Oil-based poly is similar but slightly less forgiving. It has a tendency to bubble if you overwork it. The trick is to brush it on and walk away. Stop fiddling with it.

Water-based poly is the fussiest. It can foam, it dries fast enough to catch you mid-stroke, and it raises the grain of the wood on the first coat (requiring extra sanding). But the quick dry time makes up for it if you get your technique down.

My Decision Process (Sort Of)

Project going outdoors? Spar varnish, no question.

Table or floor getting heavy use? Oil-based poly.

Light-colored wood I want to stay light? Water-based poly.

Traditional furniture where aesthetics matter more than durability? Varnish, or maybe wiping varnish for more control.

Shop furniture or something that needs to be done today? Whatever can I grab first.

The Yellowing Problem

Oil-based anything yellows over time. This is especially visible on light woods and white or pale painted surfaces. My wife’s white bookshelf, which I finished with oil-based poly because it will be more durable, is now distinctly cream-colored. She reminds me of this occasionally.

Water-based poly does not yellow. If you are finishing white oak or maple and want it to stay its natural color, this matters. Varnish yellows even more than oil-based poly, so it is really not the move for light woods unless you want that aged amber look.

Cleanup and Environmental Stuff

Oil-based varnish and poly need mineral spirits or paint thinner for cleanup. These are flammable, smelly, and you need to dispose of them properly. Rags soaked with this stuff can spontaneously combust – this is real, not an urban legend. Spread them flat outside to dry before trashing.

Water-based poly cleans up with soap and water. Much nicer. Lower VOCs too, which is better for you and the planet. It still smells like chemicals while wet but nothing like the oil-based versions.

My Current Stash

I keep three finishes on hand:

– Helmsman spar varnish for outdoor stuff
– General Finishes Arm-R-Seal (which is technically a wiping varnish with poly mixed in, go figure) for most furniture
– Minwax Polycrylic (water-based) for light woods and quick projects

Between those three, I can handle about 95 percent of what comes through the shop. The other 5 percent usually involves me standing in the finish aisle reading labels again.

Look, finishing is complicated. Anyone who tells you there is one right answer for all situations is selling something. The best finish is the one that works for your project, your timeline, and your skill level. Sometimes that is varnish. Sometimes that is poly. Sometimes that is whatever is left in the can from last time.