I've been refinishing vintage loudspeakers (Dynaco A-25s, Large Advents, AR-3as, etc.) for almost two years now. The wood I work with is usually walnut, and the grain is absolutely beautiful once you lightly sand to remove thirty years worth of spills, scuffs and scratches.
Once the speakers are sanded and oiled, I need something to seal the deal: to lock in the natural color of the oiled wood and protect it from drops of water which can lighten an oiled and hand rubbed surface.
For the last stage of my refinishing, I had until recently been using Varathane oil based clear satin polyurethane in the spray can. It yielded a natural looking finish while giving the surface just the degree of uniformity and protection I desired. But it took a long time to dry (several days, really) and didn't seem that cost-effective. I could see much of my spray disappearing into space, and a $7 can was only good for about three pairs of 24 x 12 x 12 inch speakers.
A few months ago, I started using Minwax Fast-Drying Polyurethane Satin in a can (also oil-based). A friend had recommended it, and I liked the idea of using something I didn't have to spray on. I use an old sock to apply the Minwax polyurethane, wait a few hours, and then smoothe with 0000 steel wool. A quart can of Minwax Fast-Drying Polyurethane Satin costs about $8. A half-pint can costs about $4.
Minwax claims that their canned polyurethane is fast drying, and I thought it might be more cost-effective as well. The directions explicitly say stir before using, and never shake, so that's what I've done.
Minwax Polyurethane has a smooth consistency, and is easy to apply. It's thinner than most paints, but thicker than water. It's thin enough to drip a bit, but thick enough that running over edges is relatively rare. I wipe the excess on the lip of the can with each dip, and then use relatively long strokes to apply it to the surface. You can apply multiple coats if necessary, so I try to keep each coat relatively thin.
It starts to dry pretty quickly, so by the time I'm working at the far edge of a 12" x 24" speaker side, the near side is setting up. Absolute uniformity is not necessary, assuming you're going to smoothe with steel wool once the surface dries, but it's a good idea to get things as uniform as possible.
Appearance and tweaking.
I believe Minwax Fast-Drying Polyurethane comes in three degrees of glossiness: satin (reviewed here), semi-gloss, and gloss. Satin most closely matches the original finish of most vintage speakers, so that's the only one I have used.
After a few hours (at room temperature), Minwax Fast-Drying Polyurethane is either dry or only very slightly tacky, but I tend to wait overnight before touching a polied surface. It dries slightly shinier than the Varathane spray clear satin polyurethane I had been using, but when you lightly "sand" with a fresh pad of 0000 steel wool, the appearance becomes both smoother and more matte, or dull. With experience, you can manipulate both the tactile smoothness of the surface and the amount of shine. I like to view my finished surfaces at an angle with natural light coming in through the window to make sure things are perfectly smooth and streak-free. If I am not satisfied with the results with one coat, I'll apply one more coat and steel wool it the next day. If the wood you're working on is very light, the Minwax Polyurethane will very slightly darken the appearance in some cases. Every speaker surface I have finished with this product has turned out well.
I have also done some coarser work with this polyurethane, refinishing some outside chairs out on my deck. After sanding with 60 grit, and then 150, I applied Orange Oil (this darkens things up a bit and restores moisture to the wood), and then finished with Minwax Fast-Drying Polyurethane Satin. The results are fantastic; the wood grain in the chairs shows through, the appearance is natural, and my XX (female) friend said they would easily pass the "nylon test."
Recently, I have been using Minwax Fast-Drying Polyurethane Satin more often than the Varathane oil based clear satin polyurethane in the spray can that I used to use. Both can be steel wooled down once they dry, but the Minwax dries much more quickly, allowing me to get my projects done much faster. The Minwax DOES also seem more cost-effective; I have done several pairs of speakers with my current one quart can, plus the outside project I mentioned. With the spray, I'd be on my third can by now.
Both the Minwax and the Varathane polyurethane have a fairly strong smell while you're using them, so I recommend you use either in a well-ventilated place. However, the canned Minwax puts out much less of an odor while it's drying, allowing me to bring the speakers into the house as they dry.
As mentioned, the Minwax Fast-Drying Polyurethane dries just a touch shinier than the Varathane oil based clear satin polyurethane in the spray can, so you'll need to learn how to cut the shine back a bit with steel wool if you want the same look you'd been getting with the spray can. Occasionally, once I know I'm essentially done, I'll spray a very light coat of Varathane on top of my finished speaker, just to add a touch of grain to the feel and look.
Both the spray Varathane and the canned fast-drying Polyurethane containers can develop problems over time. The spray nozzle of the Varathane tends to clog up after awhile, and though I've heard of various methods for clearing it up, I've never gotten a really uniform spray once the nozzle starts to go bad. With the canned polyurethane, it's easy for a bit of the product to get into the gap around the edge where the lid is supposed to go, leading to a less-than-air-tight seal. The result is a layer of dried poly on the surface of your poly, resembling the ice on a Minnesota lake in early winter. That happened to me, so I've vowed to be more diligent about cleaning the rim of my next can of Minwax Polyurethane.
You can clean up with mineral spirits, but I just use an old sock and toss it when I've used up the soft areas.
I think this is great stuff. It goes on smoothly, dries fairly quickly, and yields professional-looking results. It does dry just a touch shinier than the spray poly I was used to, but this won't be an issue for most people trying the product. In addition, you can cut back the shine with no problem, as Minwax polyurethane responds well to a light sanding with very fine steel wool.
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