POLYURETHANE FINISH: Power Buffing for Flawlessly, Glass-Smooth Results

 

UPDATED 4Dec2017: Buffing wood is the best-kept secret of the wood finishing world.  That’s a great thing because so many people have trouble creating a finish they can be proud of. It always surprises me how few people interested in wood have discovered the value of buffing. It can create a glass-smooth finish, even after polyurethane has been applied not-too-well with nothing more than a brush in an ordinary home  workshop. Buffing is especially valuable for dealing with the nasty side of waterbased urethane – the brush strokes, the bubbles and the less-than-smooth results many people struggle with. The dirty little secret of the wood finishing world is that waterbased urethane is significantly harder to apply well than its oil-based ancestor. Buffing really does make it easy to get superb results on wood finished with polyurethane. That’s what you’ll learn about here. Buffing works beautifully, even if you’ve applied a finish that’s not too smooth to begin with.

Most ordinary people who attempt to apply a polyurethane finish wood eventually resign themselves to sub-standard results, all for lack of one tiny piece of information. But a rough, ho-hum wood finishing outcome isn’t inevitable when you understand how to do power buffing. It works perfectly on all flat wooden surfaces, making use of the ubiquitous random orbit sander power tool. I’m not talking about using this sander for sanding, but rather for buffing a finish that you’ve already applied.

You can power-buff all kinds of finishes – wood, metal, and even car bodies. When you get to the bottom of this article, check out my video on how I used buffing techniques to get rid of scuffs and scratches on my vehicles.  In this article I’ll show you how it applies here to a polyurethane wood finishes — either oil-based or water based. Buffing can transform an ordinary wood surface into one that’s a smooth as glass and very inviting to the touch. And the work takes just a few minutes. Click the window below to watch an overview of the power buffing process.

Before you do anything else on an actual project, read and understand all the steps below.

Polyurethane Finish Tip#1: Start With a Thick Coating

The first thing to understand is the need to begin with a thick polyurethane finish film to ensure that you don’t buff right through to bare wood. That’s not to say you should apply each coat thickly. Four regular coats of urethane applied one over the other is a good starting point. Sand lightly with 240-grit sandpaper between coats, then let the last coat dry for at least 24 hours. This is standard practice with any wood finishing job, and is nothing out of the ordinary. That said, sanding bare wood beforehand to create a smooth foundation is key. Click to watch the video on the right to see how I’ve been sanding wood as a professional cabinetmaker since the mid-1980s.

Polyurethane Finish Tip#2: Level the Surface of the Polyurethane

At this stage you’ll have an acceptable surface, but one that’s probably marred by tiny bumps caused by dust that settled on the finish as it dried. This is why leveling is the pre-buffing step required next. Start with one of the old pieces of the 240-grit sandpaper you used to sand between coats earlier, then wrap it around a block of Styrofoam and rub the wood surface lightly in the same direction as the grain. It only takes a few strokes to remove the dust bumps, so don’t overdo it. Also, be sure to avoid fresh sandpaper for this job because it cuts too aggressively. You definitely don’t want to go right through the finish to bare wood. Like I said, use a piece of old 240-grit sandpaper left over from the sanding you did between coats of urethane.

After just a few strokes you’ll find that the surface feels noticeably smoother right after de-bumping, though the sheen will be irregular to the eye. It will be dull where the sandpaper did most of its work, and shinier where it did less. This is normal. As long as the surface feel perfectly smooth, it’s time to move on to the next step.

Polyurethane Finish Tip#3: Power Buffing the Levelled Surface

polyurethane finish buffNow comes the fun. It’s time to power buff. Grab your random orbit sander tool and a piece of superfine 3M rubbing pad. This is a thick, non-woven, synthetic abrasive material available at woodworking outlets and better hardware stores. It comes in different abrasive ratings, and the superfine type is what you need (it’s usually white in colour). I buy mine by mail order from Lee Valley Tools (800-267-8767). Cut a 6-inch x 6-inch piece, place it on your project, then put your sander on top. Switch on the power. As the vibrations and rotations of the tool are transmitted to the pad and the wood, it buffs the surface, removing tiny imperfections while leveling out the sheen beautifully. Work over the whole area evenly and slowly in a grid pattern. A bright light reflecting off the surface at a shallow angle is the best way to highlight areas that need more work. The more you polish, the shinier the results.

You won’t be able to get a sander into every nook and cranny, and that’s why you should prefinish parts as often as possible before assembly. You can also extend the reach of the buffing treatment using the rubbing pad by hand. You’ll find that the process also works on curved surfaces and trim if you use #0000 steel wool. This ultra-fine abrasive is excellent for buffing, but there’s a danger. Even though it’s metal, fine steel wool can catch fire and burn easily. Store it in a tightly-sealed metal can for safety. Finish up with a coat of paste wax, also buffed out under power, and you’ll have the smoothest possible finish that can be put on wood. You won’t be able to resist running your hand over it.

Got some scratches on your car or truck? Buffing might be able to help with that, too. Click below to watch how I use the process successfully, including the kind of rubbing compound that makes it work.


Polyurethane Finish Q&A

Q: Can I buff a used table that has a pretty good finish?  There are minor scratches that you can see, with a few that can be felt with your fingernail. Nothing deep, but a couple of nicks through the finish that I’d planned to touch up with  Polyshades. So, can I buff as you described, minus the 320 grit on the foam block? I have a 6″ orbital polisher to work with.  Lord, how I’d wish I’d known of buffing years ago. Always spent hours trying to get that perfect result. Sprayed a coffee table couple of years ago but got a little overspray of varnish. Can I buff that now, too?

A: I’d definitely start by coloring the minor scratches with Polyshades as you planned. After that, do some gentle buffing and see what happens. I think you’ll be pleased. And you’re right. No sanding with 320, just gentle buffing. You don’t know how thick the existing finish is, so take it easy.
As for your coffee table, yes, it’s definitely a candidate for buffing, even now. Use the 320-grit paper on a foam block to knock off the dust bumps, the go at it with a “fine” 3M rubbing pad. That’ll give you a nice, matte finish. A little work with the “super fine” will bring up a gloss. The more you use it, the shinier things get. But it’s not like the shine of gloss urethane, which I always find goopy and bad looking. A buffed gloss is a much more refined shine. I hope this helps. Please let me know how you make out.

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Posted on April 3rd, 2017

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