Rob from Make Things shared the woodworking tip featured in this video.
Using a solid white oak toilet seat as an unconventional but effective example, Rob walks through the full process of applying an oil-based polyurethane finish. The techniques covered apply just as well to tables, cabinets, or any other project that needs a durable, film-building finish.
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Preparing the Surface
Rob emphasizes that the quality of a polyurethane finish depends far more on the wood surface underneath than on the poly itself. Since polyurethane is not paint, it won’t hide scratches, dents, or glue spots. Instead, once it darkens the wood and creates a reflective film, it can actually make imperfections more visible.
He works through a sanding progression, moving from a coarser grit up to a finer one, with each step removing the scratches left by the last. Rob points out a common myth that higher grits always produce a smoother final finish. Since polyurethane is a film-building product, once the sanding scratches are invisible to the eye, going any finer on bare wood won’t improve the poly’s final surface.
Softening sharp edges with a few light sanding passes is another step Rob highlights as easy to overlook. He compares it to coating a nail, where finish builds evenly across a flat surface but thins out around sharp points. Rounding edges slightly allows the finish to build more evenly and resist damage over time.
To catch anything missed during sanding, Rob uses a raking light aimed across the surface at a low angle, similar to how the sun casts long shadows across a landscape. This method reveals scratches, dips, and raised spots that would otherwise go unnoticed. After correcting any flaws, he vacuums the surface thoroughly and wipes it down with a lightly dampened cloth using mineral spirits, which also temporarily darkens the wood to reveal any remaining imperfections.
Applying the First Coat
Before opening the can, Rob stresses the importance of stirring the polyurethane thoroughly, making sure to bring material up from the bottom rather than shaking it, which can introduce bubbles. He recommends a natural bristle brush for oil-based poly, though some products allow for a foam brush as well.
Starting on the least visible surface, Rob applies the finish in light, overlapping strokes to maintain what’s known as a wet edge. This prevents one section from beginning to dry before the next stroke connects with it, which helps avoid visible lap marks in the final finish.
After coating one side, he flips the piece to reach the other, using a simple support setup with holes so both sides can be finished without direct contact. Once the entire surface is covered, he finishes with a technique called tipping off, using just the tip of the brush in a few light, feathering passes to smooth out brush marks and break up small bubbles. This step needs to happen while the poly is still wet, since going back over a tacky surface can create new marks instead of removing old ones.
Building the Finish Between Coats
Once a coat starts to dry, the temptation to rush into sanding and recoating can lead to problems. Rob points out that drying time is affected by several variables, including temperature, airflow, and humidity, so patience matters more than the clock.
To check if a coat is ready, he tests a small hidden area with sandpaper. If the sanding produces a fine, dry powder, the coat is ready to be worked on. If it gums up or smears instead, more drying time is needed.
The goal during this stage isn’t to scratch up the surface for adhesion, since oil-based polyurethane naturally bonds well between coats, especially when little time passes in between. Instead, sanding is used to knock down small dust nibs and raised imperfections until everything feels smooth to the touch. Careful attention around edges helps avoid accidentally sanding through the built-up finish.
After sanding, all dust needs to be removed with a vacuum, followed by a light pass with a tack cloth. Rob cautions against pressing too hard with the tack cloth, since that can leave a sticky residue that interferes with the next coat.
Final Coats and Curing
After building up several full-strength coats, Rob switches to a thinner half coat made of equal parts polyurethane and mineral spirits. Thinner coats dry faster, which reduces the amount of time dust has to settle into the wet surface.
Once that coat dries, a finer grit sandpaper is used to level out any remaining nibs or brush marks before the final coat goes on. The same rule applies throughout the process: if the sandpaper clogs instead of producing a fine powder, the finish needs more time before sanding.
Even after the final coat looks complete, Rob notes that it isn’t ready for full use right away. Curing time varies based on environmental conditions, and rushing this stage can undo all the careful work that came before it.
The Paper Bag Trick
After the finish has hardened for several days, Rob demonstrates a technique credited to finishing expert Bob Flexner: using a plain brown paper bag to gently smooth out any remaining dust nibs. A section of the bag is folded into a smooth pad rather than crumpled, then used to lightly buff the surface.
This method is tested first on an inconspicuous area to check for scratching. If scratches appear, the finish likely needs more curing time before trying again. Rob is careful to note that this technique only addresses small dust nibs, not runs, brush marks, or larger surface flaws.
Why the Process Matters
Rob’s breakdown shows that a strong polyurethane finish comes down to patience and attention to detail rather than any single product. Proper surface prep, controlled coat application, and careful sanding between layers all play a bigger role than the polyurethane itself.
Whether the project is a tabletop, a cabinet, or something as unconventional as a toilet seat, the same fundamental steps apply. Taking the time to check for readiness at each stage, rather than following a fixed schedule, leads to a smoother, more durable result.
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Matt’s Take
These are my personal thoughts and tips based on my own experience in the shop. This section is not written, reviewed, or endorsed by the original creator of this project.
Rob’s point about surface prep mattering more than the poly itself is something I’d echo to anyone starting out with film finishes. It’s tempting to think a good finish can smooth over a mediocre sanding job, but oil-based poly actually magnifies flaws once it darkens the wood and lays down that reflective film. Raking light is one of the best cheap tools in the shop for this — a $10 work light held at a low angle will show you more than staring straight down at the wood ever will.
On the brush side, natural bristle really is the way to go with oil-based poly. Foam brushes can work in a pinch, but they hold less material and tend to leave a thinner, less controlled coat, plus they can shed tiny bubbles into the finish if you push too hard. If you go the foam route, just slow down and use lighter pressure.
One thing worth keeping in mind with any oil-based finish is ventilation and disposal. These products off-gas solvents as they cure, so good airflow in the shop isn’t optional. And oily rags aren’t something to toss in a regular trash can — laid flat to dry outside or stored in a sealed metal container, they’re far less of a fire risk. It’s a small step, but it’s one of those safety habits worth building early.
The paper bag trick is a great example of how a lot of finishing knowledge is just clever, low-cost problem solving rather than needing specialty products. Testing in an inconspicuous spot first, like Rob does, is good practice anytime you’re trying a new technique on a finish you’ve already invested hours into.