Michael Dresdner

Q: I am pre finishing a large two piece conference table. I finished spaying a heavy coat of my last application of flat pre cat over two coats of vinyl sealer and two coats of flat. The temperature here is in the 80′s with about 28% humidity. I plan on wrapping these tops in shipping blankets laying one on top of the other for a 1500 mile delivery. How long should I wait until the finish is hard enough not to mar or rub?
A: That’s not as simple a question as it appears. There are two variables that you did not tell me, so the best I can do is give you a rubric for figuring it out, and that includes explaining the cure variables you are working with.
First, understand that catalyzed, and especially pre cat mixtures, vary tremendously in cure time depending on their formulation. Specifically, the higher the acid content the faster the cure, but there is no standard. Thus, you need to read the spec sheet; it should tell you when full cure occurs. Typical formulas can range from as little as eight hours to eight days, and that’s for one coat on an already cured surface. That brings us to number two.
Second, this will all change if the four base coats of vinyl and flat were not catalyzed. If they were not, it greatly extends the time needed to prevent blocking. As I said, since I am lacking these critical bits of information, I can’t give you a solid time. However, it won’t hurt to do a thumbnail test. Find an inconspicuous spot and press a thumbnail into the finish with more pressure than you suspect will be exerted by the shipping weight. That will at least give you insight into how the finish is geared up to resist an impression from the pads.

Q: I recently purchased a quart of Bartley Gel Varnish over the internet. The product I received is Bartley Gel Stain – Clear Satin. Is this the same as the Bartley Gel Varnish?
A: Yep. The best I can figure is that Bartley started as a one step wipe on stain and finish, sold as an “all you need do is wipe on the stain and you’re done” panacea. That started people referring to what was actually a tinted finish as a stain. It made sense to keep the familiar name for the clear version. The same gestalt exists in deck coatings; most are technically tinted finishes, but are called stains.

Q: How can I produce a driftwood finish, like the one in this picture? I am thinking of using bleach, chemical stains and dye rather than paint or pigment stain.
A: I have to say that the photo you sent looks nothing like what I would call driftwood. In fact it looks like roughly prepared wood with open cracks and grain raised with water that has been sealed with an off white toner, wet glazed with burnt umber, then topped with dead flat clear; a rather classic antique finish. If that is what you want, that’s how to recreate it. If, on the other hand, you want driftwood, try this.
Raise the grain by flooding the wood with water, wiping off the excess, then leaving it overnight to dry. Add cracks if you choose, or distress marks, if that is what you like. Mimic erosion by scrubbing the wood aggressively with a wire brush. This works best on softwoods whose early wood bands abrade more quickly than tougher late wood ones. Add black and off white paint to their solvent to make a quick stain, but mix only perfunctorily. A piebald gray is the goal here. Wipe the paint onto the wood and off. You should have areas of lighter and darker gray that looks similar to real driftwood.

Q: I am making a cabinet door of solid cherry with a quilted maple panel. I want a bit of contrast between the cherry and maple and to show off the quilting in the maple. I was planning to stain the maple with a cherry color oil based stain and sand it lightly with 600 grit before applying wipe on polyurethane on the entire door.
A: Most quilted maple is western bigleaf maple, and unlike its eastern rock maple cousin, will absorb some pigmented stain. However, the ideal way to intensify grain in maple is to go with something that has a lower molecular weight. In the case of stains, that would be dye. A weak dye, flooded on and wiped off, will intensify the quilt pattern as well as adding color. Of course, an oil based finish, such as wipe on polyurethane, will add a slight amber color, which will also intensify the grain. In short, you don’t need stain to bring out the grain, though if your goal is to change the color to match the cherry, yet still pop the grain, dye is the way to go.

Q: What makes an alkyd oil based enamel usable for interior use but not for exterior use? Can I tell from looking at the MSDS?
A: There are three basic elements that make that difference, and unfortunately, that is not clear from reading an MSDS. They are the resin, the colorant, and the pigment loading.
Resins can be either exterior or interior. For example, linear or aliphatic polymers, such as linear urethanes, are generally light stable and can be used outdoors, while aromatic or non-linear ones are usually not. In addition, the resin must be sufficiently flexible so as to weather the wide range of wood movement experienced outdoors. Many resins, while lightfast, are too brittle for that. For instance, oil based alkyd resins can be made more or less flexible depending on whether they will be for indoor or outdoor use. You may have heard the terms “long oil alkyd” used for exterior paints and “short oil alkyd” for interior ones.
Second, there are some coloring agents that are lightfast and others that will break down in sunlight. Finally there is the pigment loading, a ratio of pigment to resin. To survive outdoors, not only must the pigments and resins be exterior capable and lightfast, but the pigment must be in the right proportions so that the entire mixture does not chalk or break down. Ceiling paint, for example, is meant to hide quickly but does not need weathering characteristics, and is typically made with extremely high pigment loading. Kitchen or bathroom paint designed to be scrubbed clean will have a higher resin proportion, as will most exterior paints.
In short, both the elements and proportions control exterior suitability, so looking at the MSDS alone will not necessarily tell you that.

Q: I made some replacement handgun grips of cocobolo. Realizing that cocobolo has a lot of natural oils in it I first sealed it with shellac, then filled the pores with a product called z-poxy. I then sanded and applied one coat of Minwax polyurethane. Three weeks later I can make a thumb print in the finish. I think I sanded through my seal coat, because the poly is not curing. Can I remove the uncured poly with mineral spirits?
A: I doubt it, unless it is still fully liquid. What typically happens is that exposure to the raw cocobolo (where you sanded through) will inhibit the cure of an oil based finish, but not keep it entirely liquid. Thus, it stays tacky or gummy.
You’re certainly welcome to try scrubbing off the finish with mineral spirits on a coarse nylon abrasive pad, but in most cases you will have to resort to at least refinisher if not stripper. Since the parts are so small that should not be a big deal. You can also sand back to raw wood, again, since the parts are so small.
For the record, the reason oil based finishes don’t cure over dalbergias, such as cocobolo, has nothing to do with the wood appearing oily. In fact, it contains resins, but not, strictly speaking, oils. The problem is that the wood also contains a natural anti-oxidant.
Think of how citric acid, another natural plant anti-oxidant, slows the oxidation and browning of freshly cut apples if they are dipped in lemon juice. The anti-oxidant in dalbergia woods does the same thing.
Oil based polyurethane and varnish cure by oxidation polymerization; they take oxygen from the air and use it to link up small molecules to make large ones, thus turning a liquid finish into a solid film through chemical linking. The anti-oxidant is the culprit in delaying or preventing that chemical reaction.

Q: The kitchen cabinets in my 20 year old house were painted rather than stained. They are a cherry color on what I believe is alder. Over the years some of the paint has chipped away leaving behind part of the original unfinished wood. The cherry paint itself is not a solid color, but varies in color a bit. Can a handy person do a decent patch up job?
A: Absolutely, but it helps to know what you are dealing with, and it’s not paint. It’s called toner, which is clear finish with some color added to it, though not as much color as would be in an opaque paint. Instead of staining the wood, the wood is sealed, then sprayed with layers of semi-transparent color until one gets a uniform tint. Spraying more means darker, more opaque color; less gives lighter, more translucent color.
Because that is such a common method of coloring cabinets and furniture, there are common repair materials available to do touch up. They come in two distinct types; pens and aerosol cans. Touch up pens are essentially felt tip markers made in common furniture finish colors. You use them just as you would a marker, simply coloring in the light areas to match. You can also find aerosol cans of toner or tinting lacquer which you spray on the area to blend in the color. Both are quite easy to use. Just make certain you clean the area, or better yet, the entire cabinet, with a good degreaser first to ensure good adhesion. The cheapest effective cleaner is mineral spirits, also sold under the name paint thinner.

Q: I am finishing alder with Daly’s Benite and CrystalFin, spraying with a Fuji gun and #55 needle. I have been using water damp cloths as tack rags. I am getting white spots in the dried finish. Most areas are fine, but some of the areas look like white overspray. The spots are down in the cured finish. I did not apply a sealer. Could this be an issue?
A: Probably not. The most common cause of white in waterbased coatings comes from applying it too heavily, or working in conditions where the water does not have time to evaporate before the finish starts to cure. Try spraying thinner coats, work on days when the humidity is low, or add a slowing solvent to the finish.

Q: I need to know if d-limonene will harm cured nitrocellulose lacquer. I want to use it as a solvent in a 25% mixture with mineral spirits.
A: No, d-limonene will not harm lacquer. It is one half of the racemic mixture called dipentene, and for all intents and purposes as far as finishing and cleaning are concerned, it is completely interchangeable with mineral spirits. There’s no difference in how they behave. The only real difference would be price due to derivation; inexpensive mineral spirits comes from petroleum, while the decidedly more expensive dipentene is extracted from citrus fruit peel.
In case you were curious, the d-, which stands for dextrorotatory, or right hand rotation, is generally lower case in chemical notation. It’s fellow traveler in the racemic mixture is l-limonene, for levorotatory. Racemic mixtures contain equal amounts of left and right mirror image versions of the same molecule.

Q: We are getting an increasing amount of mineral calcium deposits in rosewood. Do you know of an effective way to remove them, aside from the acids that are currently available?
A: No, but to be honest, muriatic acid, which is cheap and easily available, works so well and so quickly with most mineral deposits that I never bothered to look for an alternative. The fact that acids, unlike bases, do not discolor most woods keeps it the favored choice for that problem.