Polyurethane and Outdoor Cedar Furniture Just Don’t Mix
When it comes to protecting outdoor furniture and in particular cedar furniture, it might seem logical to apply a durable, protective finish like polyurethane. After all, polyurethane is known for its toughness and glossy finish on indoor wood surfaces. But when applied to cedar furniture like swing sets and picnic tables used outdoors, polyurethane often causes more problems than it solves. Here's why putting polyurethane on outdoor cedar furniture is generally not recommended…..and what to do instead.
Polyurethane is not made for outdoor use. The first and most important reason is that most polyurethanes are designed for indoor use. They aren’t formulated to withstand UV rays, varying temperatures, or constant moisture. Outdoor elements quickly break down the finish, causing it to crack, peel, and flake.
Even when labeled as “exterior polyurethane,” these finishes often degrade faster than alternatives specifically made for outdoor use. Once the seal is compromised (maybe knocked by a falling limb or the wood itself cracks), water seeps in, getting trapped under the finish and causing mildew, rot, or wood discoloration.
Cedar needs to have the ability to breathe. It is a naturally rot-resistant wood with oils that help it resist moisture and repel insects. One of the key advantages of cedar is that it doesn’t necessarily need a heavy finish to perform well outside.
Polyurethane forms a hard, non-breathable shell. Cedar, however, is a porous, living material that expands and contracts with changes in humidity and temperature. When you seal it with an impermeable coating like polyurethane, that natural movement is restricted, increasing the risk of cracking and splitting.
Polyurethane itself is difficult to maintain and recoating is needed regularly. Let’s say the shell coating does crack, correcting and maintaining it is labor intensive. Once polyurethane begins to fail outdoors, refinishing is not easy. You can’t simply touch it up—you have to strip it entirely and reapply, which can be a labor-intensive and frustrating process. Stripping chemicals can damage the wood, and sanding soft cedar must be done with care to avoid gouging the wood.
What we recommend as better alternatives are the following:
• Penetrating oil finishes (like tung oil or linseed oil) allow the wood to breathe while offering water resistance and enhancing grain.
• Exterior wood stains with UV inhibitors help protect against sun damage while maintaining a more natural look.
• Clear outdoor sealers designed for cedar (like Cabot water-based wood sealer) provide a degree of protection while being flexible enough to move with the wood.
Water based alternatives are easier to maintain and reapply, and they work with the wood, not against it. Oil based alternatives are also easier than polyurethane but are harder to apply and clean up for the novice. If you want more guidance on what to use, we have another article entitled Oil Based Stains vs Water Based Stains or Types of Stains & Sealers that can give you further guidance.
Cedar is naturally beautiful and durable—protect it with products that complement its nature, not suffocate it. Apply the correct sealer for at least the first two years and you'll save yourself time, effort, and preserve the life and look of your outdoor furniture for years to come.
