Michael Dresdner » polyurethane

Glazy days of summer

Michael — Mon, 30 Aug 2010 14:00:05 +0000

Q: I’ve stained and sealed with Zinsser SealCoat and plan to glaze with a Van Dyke oil-based glaze. I wanted to top with Zar Interior Polyurethane antique flat, but Zar says polyurethane will delaminate off either the glaze or SealCoat, which has no wax, but may contain stearates. Now what?
A: First, SealCoat contains no stearates and is perfectly compatible under both oil based and waterbased polyurethane. Second, oil based polyurethane will bond just fine to oil based glaze. The problem, and it has nothing to do with Zar or any other polyurethane for that matter, comes if you leave too much glaze on the surface, or if you mix the glaze with insufficient binder.
Whether a coat adheres to the previous coat is only half the problem. The other half is the integrity of the middle coat itself. If you create a glaze made of pigment with so little binder that when it dries, it acts like a barely held together layer of pigment powder, it will be the weak layer in your finish. Even if finish sticks to the top of this glaze layer, and it sticks to what is beneath it, if the layer itself breaks apart, you have delamination.
The key, then, is either to make sure you add very little glaze before sealing, and you can do that by glazing several times if need be with sealer between each application, or use a glaze that has enough binder to maintain its own integrity as a coat of finish.

Oil based lacquer?

Michael — Thu, 19 Aug 2010 14:00:04 +0000

Q: Can I put oil based wiping polyurethane over oil based spray lacquer?
A: The simple answer to your question is yes, you can put oil based polyurethane, whether wiped, brushed or sprayed, over almost anything, including lacquer. For the record, though, lacquer is, by definition, an evaporative finish, while oil based finishes are, by definition, reactive. In other words, the terminology indicates the process by which the finish goes from liquid to solid film. Thus the term “oil based lacquer” is at best a misnomer. While one could make an evaporative finish using a stable resin derived from oil, that should still be called simply lacquer.

Gel varnish, still hiding

Michael — Wed, 07 Jul 2010 14:00:28 +0000

Q: I have used the gel varnish that was sold at Rockler for a number of years with outstanding results. Since Rockler no longer carries it and there appears to be a company change taking place I am wondering if there is another brand of gel varnish you recommend.
A: That particular gel polyurethane was made by Lawrence McFadden and sold under several labels, including Rockler, Bartley and LMcF. The company was recently sold to Seagrave Coatings. Seagrave’s owner tells me there were a few problems with packaging and logistics that caused delays. You can expect to see the gel by early August in your favorite store. It will be sold under the Bartley label in both clear and colors.

Hungry rocker

Michael — Fri, 18 Jun 2010 14:00:50 +0000

Q: I just finished my fifth Maloof style rocker and have not been happy with finishing results yet. On the latest I just applied my second coat of Danish finish. I followed the instructions and wiped both coats dry. I want more shine; what can I put on top of the oil?
A: You have several good options. You can continue with more coats of Danish oil, though it will take at least a dozen before you get any noticeable sheen. You can also switch to wipe on oil based varnish or polyurethane, which will be just as easy and will build a bit faster. Or, you can go to a brush on varnish or polyurethane for the quickest build and highest shine.

No fade, no shade

Michael — Tue, 15 Jun 2010 14:00:10 +0000

Q: We are in the process of making a dining room table out of solid padauk and purpleheart, and wanted to know the best way to finish it. We would love to be able to keep the colors of the natural wood, without ambering over time. A clear, durable finish would be great as well.
A: For a clear durable finish that will not amber over time use a waterbased polyurethane. It goes on clear and will not amber. For more durability, use a cross linking waterbased floor finish. However, neither of those will prevent the sun fading the wood. For that you’d want an exterior waterbased finish that contains UV absorbers and blockers, but it will be softer and not as durable. Even at that, it will only delay the fading of the wood colors, not stop it entirely. Sadly, finishing, like life, is full of tough choices.

Fishy finish

Michael — Mon, 07 Jun 2010 14:00:06 +0000

Q: I stripped an oak fish tank stand and applied two heavy coats of espresso colored Varathane oil stain, leaving it sit one hour before wiping it off. I then applied two heavy coats of Watco Teak Oil and left them overnight. I found a sticky, gooey mess in the morning. When I tried to remove it using more Teak Oil, much of the color came off as well.
A: I am not surprised. Stain is meant to be wiped on and wiped off completely, leaving only what the wood can absorb. Layering it on heavily or leaving it longer won’t result in anything but trouble. Granted, more porous woods, like poplar, will absorb more stain than a dense wood like oak, and will get darker. The fact that stain came off when you scrubbed off the excess finish is an indicator that you left more on the wood than it was able to absorb.
The way around that is to use multiple types of color, not try to force one stain to override the nature of the wood you are putting it on. For instance, to get a very dark espresso, I’d start with a dark brownish black water soluble dye directly onto the raw, sanded wood, then follow that, when the dye was dry, with a dark wiping stain flooded on and wiped off. The combination will give you a dark, even color with wood grain still showing.
Teak oil is also meant to be wiped off in 15 minutes, not overnight, and letting it sit that long will indeed create a sticky mess. The simple answer is you really should read the directions and do what they say. At this point, you would be very wise to remove it all and start over.
Incidentally, Teak Oil, which is the exterior version of Danish oil, is not the finish I would have chosen in this case, for a variety of reasons that I have covered in previous posts. I’d have chosen an oil based polyurethane, either wipe on, gel or brush on, and I would go with several coats at least.

Flat out no

Michael — Wed, 26 May 2010 14:00:41 +0000

Q: I love gel polyurethane but I was wondering if there is some kind of flattener you would recommend that could be used in it to make it flatter than satin.
A: No, there is nothing you can add easily, but there are certainly ways to control the sheen. Bear in mind that is a wipe off finish; the coarser the substrate, and the thinner the finish, the duller its appearance. In other words, start with wood sanded no finer than 180, wipe on the finish, and wipe it all off. Stick to two or thee coats, one per day, each wiped off completely, and you will have a very low sheen. For thicker finishes, lower the sheen by rubbing with the grain using fine steel wool. You will find dry 0000 steel wool will give you a lower sheen than rubbing with steel wool lubricated with wax. Finally, for a thicker finish, you can also sand the final finish uniformly with 600 or 800 grit paper, which will also leave a dull surface.

Hold on there, finish!

Michael — Tue, 25 May 2010 14:00:38 +0000

Q: What finish will stand up to New York winters? Sometimes the windows sweat on the inside and my finish comes off in a year or two.
A: Part of that my be your choice of finish, but it may also be the preparation. You must start with clean, sanded wood to get good adhesion, then choose a finish that is not prone to peeling and has a high moisture resistance. I’d go with oil based varnish, spar varnish, or exterior oil based polyurethane. All have good adhesion and resistance to moisture delamination.

Sometimes two is worse than one

Michael — Thu, 20 May 2010 14:00:37 +0000

Q: Is an oil/polyurethane mixture a good choice for a dining table?
A: Oil alone is a fairly poor choice. Oil based polyurethane is an excellent choice. A mixture of the two will fall somewhere between poor and excellent.

Hemp for a “high” shine?

Michael — Tue, 18 May 2010 14:00:53 +0000

Q: We used hemp oil and beeswax to finish a new very large dining room table. However, the finish is not durable and water and wine stains are a real problem. We wish to remove and re-sand it and need some advice for refinishing it. Would any other oil such, as walnut oil offer the kind of protection we need for daily use?
A: I assume you meant hempseed oil, since hemp oil, which is made from the bud and leaves and not the seed, is illegal in the US except by prescription, as it contains substantial amounts of THC. Either way, hempseed oil is not a good finish choice, and is mostly sold as a dietary supplement. I can’t imagine why someone would choose it as a wood treatment.
Though not all oils are equal, oil in general is not a good choice for something that needs as much durability as a dining table. For that matter, neither is wax. Waxes and non-drying oils are only temporary, and are best used as polishes above a finish rather than as a finish. By contrast, a drying oil, such as tung oil or boiled linseed oil, which does form a film, albeit a very thin one, is fine for art pieces, gently handled turnings, picture frames and the like. However, to resist water, wine, stains, acids, bases, solvents, abrasion and heat, all the things to which a dining table is prey, you want a more substantial film forming finish. The best choice for such durability is oil based polyurethane, which is both durable and fairly easy to apply. Some versions simply wipe on at one coat per day for as many days as it takes to build a sufficient finish.