Michael Dresdner

Urine luck

Michael — Wed, 10 Mar 2010 17:00:05 +0000

Q: I have an oak hutch that has been sprayed with cat urine some time ago. Can you help me figure out what to neutralize the urine with so I can refinish it? I’ve tried vinegar as well as carpet cleaning solution but the stains are still showing through.
A: I suspect what you are talking about is not neutralizing, which merely means changing the pH, but rather removing a stain. In almost all cases, you must remove the finish before you can remove a stain that is in the wood itself. Once you get down to bare wood, you can try a number of different bleaches and stain removers, but I will tell you that because of the diet of a cat, there is no guarantee which, if any, will work. Still, here’s what I would suggest.
Strip the finish, and lightly sand the bare wood. Wash the entire surface, not just the stain itself, with each bleach in turn. Start with a 10% solution of oxalic acid in water. Apply it liberally but evenly, so there are no puddles, and let it dry overnight. Remove any white residue with a damp cloth. If the stain still remains, do another wash, this time with full strength laundry bleach, again, wetting the wood very thoroughly but leaving no puddles. Let it dry overnight. Both these treatments remove stains without changing the color of the wood itself, and should remove urine stains in most cases. There is a more draconian alternative, a two part wood bleach, but it involves chemicals that are dangerous to handle, and will decolor the wood itself along with stains. Thus, I don’t suggest this unless you’ve had some experience handling these strong oxidizers and enough finishing experience to recolor the wood once you are done.

Dark sound, dark board

Michael — Mon, 08 Mar 2010 17:00:52 +0000

Q: I usually finish the soundboard of my classical guitars with dewaxed shellac. It has no color at all and therefore the soundboard ends up being very pale. I noticed all classical guitar sound boards are more toward a brown tint. My question is, do you think luthiers stain their soundboards only by using different shades of shellac (amber, garnet, etc) or they have some kind of stain colorant or whatever to add color to shellac?
A: Both of the above, and two other options as well. First, some builders use lacquer, not shellac, and many lacquers have a slightly brownish tint. In addition, many classical builders use western red cedar for their tops, and it is naturally browner than spruce or yellow cedar. It is also worth noting that both spruce and cedar darken over time with exposure to sunlight, and that, too, may impact the color you are seeing.

Fisheye follies

Michael — Fri, 05 Mar 2010 17:00:55 +0000

Q: I’m refinishing a mahogany end table. After stripping the old finish, I washed it down with paint thinner then applied a coat of polyurethane. The finish did not take in some areas. I believe it’s called fisheye. I applied a second coat and it seem to fill in some of the spots but enough remain to be annoying. Can I sand the finish and apply a coat of Zinsser SealCoat before continuing with more polyurethane, or should I re-strip it and start all over.
A: Yes. And by that, I mean yes to both. You can indeed take a short cut and seal the polyurethane with Zinsser SealCoat, then continue, and you will probably seal in your contamination. You can also start over, and though it is more work, it’s probably a better way to go.
If you start again, make sure all the finish is really off when you strip. It’s common, especially in large pore woods like mahogany, for finish to be still in the pores, and that can cause some of the problems you describe. Scrub the finish out using a stiff bristle brush while it is softened by the stripper. Scrub the clean wood afterward using a nylon abrasive pad with ample amounts of lacquer thinner, then mineral spirits, and finally with plenty of warm water laced with a bit of ammonia, wiping off thoroughly between each wash. That three step scrubbing sequence will help remove wax, oils and residual silicone. A coat of SealCoat on the raw wood will add an extra level of protection which is nice under oil based polyurethane, but an absolute must under waterbased.

Lathe finish, CA style

Michael — Wed, 03 Mar 2010 17:00:25 +0000

Q: How can one apply CA glue as a finish on turning projects like pens, shaving brushes, bottle stoppers, etc.?
A: Good question, but one I have already covered in this blog about this time last year. Go to the page at the link below, and scroll down. The information you want is in the last paragraph of the entry. Hope it helps! Good luck.

http://www.michaeldresdner.com/2009/02/finishing-on-the-lathe/

Oil or water, or both?

Michael — Mon, 01 Mar 2010 17:00:51 +0000

Q: I have been using Minwax Satin Oil Based Wipe-On polyurethane for finishing my kitchen cabinets. I can’t buy it anymore in California due to VOC laws. Is the water based product going to give me the same results?
A: Depending on your criteria, you may or may not find it acceptable. It is developing a good reputation and following, so it is certainly worth a try, but as always, try these things on scrap first. As a rule, abrasion resistance will not be problem, but you might want to test it once it is cured with whatever range of heat, solvents and chemicals your kitchen is likely to produce. If you decide you prefer oil based, simply buy oil based polyurethane and use that as a wipe off finish. Thin it with mineral spirits if you like, but I find scrubbing on oil based polyurethane with gray Scotchbrite right out of the can, and wiping it off immediately with paper shop towels works fine without any thinning.

Satin rub primer

Michael — Fri, 26 Feb 2010 17:00:59 +0000

Q: I recently attempted to hand rub the polyurethane finish on a mahogany tabletop that I refinished and was disappointed with the result. The top has three coats of oil based satin polyurethane. The finish had a nice even satin sheen but felt like 220 grit paper. I then wet sanded with 600, 1000 and 1500 grit wet paper wrapped around a felt block, then rubbed with FFF pumice using a felt block and water lube. What did I do wrong?
A: You did not tell me if the finish was sufficiently cured, and that alone can undo your best efforts. Even so, you are going about creating a satin finish in a most difficult way. Here’s a simpler method that may work better.
Wait until the finish cures completely. For shellac and lacquer, two or three days will do; for oil based varnish and polyurethane, try to wait three weeks, and longer if you can spare the time. For waterbased, wait a month.
Smooth the top surface, removing any dust nibs, by sanding lightly with 400 grit self lubricated sandpaper. Sand only enough to remove the nibs – don’t over sand. Dip a pad of 0000 steel wool into paste wax and carefully rub with the grain. Do the edges first separately, as it is hard to rub all the way to the very edge of a surface. Keep your hand flat so you can rub right up to the edge without rounding the steel wool over the corner, which would cause you to rub through the finish. Once the edges are pre-rubbed, concentrate on the bulk of the top surface. Rub in very straight lines side to side, with the grain, across the entire top. Overlap your strokes and cover the entire top with at least six passes back and forth. That will guarantee a uniform fine scratch pattern from the steel wool, and the finish should look like finely brushed brass. Add more paste wax as needed for lubrication.
When you are done rubbing, immediately wipe off all the wax with a soft cloth, but that may still leave enough wax to smear. To remove it, sprinkle the top with cold water. Take a new, clean 0000 steel wool pad and gently go back and forth in the same rubbing pattern. Go over the surface once lightly, then flip the pad and do it again. Use no pressure other than the weight of your hand. The cold water will congeal the wax, allowing the steel wool to remove it. Wipe off the water and admire your work.

There’s the rub

Michael — Wed, 24 Feb 2010 17:00:18 +0000

Q: I find conflicting information as to whether polyurethane can be rubbed.
A: Any finish, including polyurethane, can be rubbed provided it is sufficiently cured. As a rule, the longer the finish cures, the harder it gets and the easier it is to rub. Attempting to rub out a finish that is still rubbery is an exercise in frustration. For oil based polyurethane, I’d wait at least three weeks to rub if at all possible, and four weeks for waterbased.

Ply your trade

Michael — Mon, 22 Feb 2010 17:00:05 +0000

Q: I would like to make some cheap instruments and use higher grade plywood. What type of filler do you think I should use to fill the plywood edges? Should I use something like Bondo?
A: Bondo, which is a brand of polyester filler with added fiber, would be an excellent choice. By the way, the highest grades of plywood, such as Baltic birch and dieboard, will not have voids, but will show layered but solid edges when routed. In that case, where you are dealing with subtle texture rather than voids, I would go with any of the many putties on the market. My favorite for a job like this would be Timbermate. http://www.timbermate.com/

Name that tune

Michael — Fri, 19 Feb 2010 17:00:19 +0000

Q: I need to put a brand name on my guitars. I’d like to use a stencil or ink stamp under the clear coat. What do you think?
A: Either will work, provided you choose the right medium for your stencil or ink stamp. What’s important is to use a paint or ink that is compatible with the finish below and above it, but not one that uses the same solvent, or the stencil or inked area is likely to spread and get blurry. There are a lot of options. For opaque ink stamp work, waterbased acrylic artist or craft paints will do just fine provided they are not applied too thickly. For stencils, you can spray on another color from an aerosol. If the finish is lacquer, you can use the same lacquer for the stencil, since it is compatible and will dry quickly enough to not create blurring problems. Beyond that you can order decals, rub on transfer numbers, use silk screening, or a host of other means to add your brand name.

The clear solution

Michael — Wed, 17 Feb 2010 17:00:34 +0000

Q: I’m finishing a guitar in Krylon Special Purpose clear Lacquer over Satin Nickel Metallic over gray primer. The clear coat has some orange peel. I’m afraid to wet sand and buff it because I previously sanded through the finish at the edges and had to start over with bare wood. Since the finish looks good, I’d like to keep using the spray paint and just change the clear coat. Should I get a compressor spray outfit and spray clear nitrocellulose over the acrylic?
A: That’s one option, but there are others, and better ones at that. For one thing, nitrocellulose lacquer is amber, and will get more amber with time, while acrylic lacquer is clear and stays that way. Thus, even if you were to switch to a spray rig, I would suggest sticking with acrylic clear topcoat, which is available from most industrial suppliers and auto paint stores. However, there’s no real reason to go that far. You can simply add more clear coats the same way you added the first; with an aerosol can. With practice you can spray without orange peel. Working in a cooler room can sometimes help slow the set up time enough to give you better flow out also. Once you have built up enough clear, you can carefully sand it smooth and add more, or if there is enough material, simply rub it at that point. Granted, it takes a whole lot longer, and many more coats, when you are using aerosol cans, but you can still get the same final results and avoid the expense of setting up a spray rig. Just be patient.