Michael Dresdner » finishing techniques

Open pore or filled

Michael — Wed, 08 Sep 2010 14:00:12 +0000

Q: I would like to use the shellac and wax finish we learned during the uke building class on a classical guitar I built, but it’s Indian Rosewood and the pores look a bit open. Do I need filler first?
A: The finish you used on your ukulele is a very thin, open pore finish. It will also work on a guitar made of open pore wood, though the pores will remain open. That in itself is not a problem; it is an option. If you like the look of an open pore finish, and I must admit that I do, there’s no reason to fill the pores.
If, on the other hand, you want the pores filled so that the surface looks more like glass than wood, you’ll save a lot of time and effort by filling the pores with pore filler before layering on finish. I should point out that pore filling is usually paired with thicker, multi-coat built up finishes that get rubbed out to gloss, not with thin, natural looking flood on and wipe off finishes such as what you have on your ukulele.

Sunburst by hand

Michael — Tue, 07 Sep 2010 14:00:04 +0000

Q: I read somewhere that the first sunburst finishes were produced by hand. Can you describe how this was done?
A: I can and have. Many years ago (1983, if I recall) I described the process at length in an article for Vintage Guitar Bulletin. That piece later became part of a small book or booklet called Restoration Clinic, which sadly, is now out of print. Though it was written on computer, those were the days of large floppy disks, and I no longer have it on media or I would simply send it to you. It’s a bit long for a blog entry, but if there was enough call for it I could retype it onto more current computer media and post it somewhere. However, to be honest, you’re the first person to ask me how to do that in years. If your goal is more than idle curiosity, email me and I’ll make it available again.

Bleeding sunburst

Michael — Mon, 06 Sep 2010 14:00:53 +0000

Q: I stained a guitar red/brown using water soluble dye. After the stain was dry, I dry brushed dark brown water soluble dye around the edges, fading toward the center for a sunburst-like finish. Clear lacquer coats finished the job. Will the dyes bleed into each other over time and become unattractive?
A: No. Water soluble dye will not bleed into solvent based lacquer. It will bleed into waterbased finish, though. However, bleeding is not your main problem.
Dye without binder added, as is typical for water soluble dye, will dry back to a powder once the water is gone. Thus, the strategy is to let it soak into wood, but wipe off anything that does not soak in. Dye brushed onto the surface and left there will dry and leave a layer of powdered crystals on the wood’s surface. That could cause future coats to delaminate, since they can’t adhere to a layer of powder unless they are able to dissolve it, and solvent based lacquer can not dissolve water soluble dye. In short, you have set the stage for your finish to peel at some future date.

Stiffness to mass

Michael — Thu, 26 Aug 2010 14:00:50 +0000

Q: I am building my 10th guitar and am using epoxy over bare Indian rosewood to fill the pores, with great success. Can I also apply epoxy to the soundboard to eliminate “spruce ripples” and also fill voids in the rosette?
A: You can, but I would not advise it, though it might make an interesting experiment for a few guitars. The problem is that softwoods, like the spruce used on guitar tops, tend to absorb a good bit of impregnating coatings such as epoxy.
The beauty of spruce is that it has a high stiffness to mass ratio. In other words, it produces good tone because it is light, but stiff. Adding epoxy to the wood will increase its mass, and is not likely to add to its stiffness. Thus, it is likely to result in a slightly duller sounding top.
That said, I do know of a number of people who use polyester as a curing filler, even on spruce. It is admittedly much more brittle than most epoxies, and therefore likely to be a bit less problematic, but I’d want to hear a dozen identical test guitars, half with and half without curing filler on the tops, before I’d be convinced there was not some loss of tone in the process.

Rattle cans are cheaper

Michael — Wed, 18 Aug 2010 16:18:10 +0000

Q: We’d like to spray Rustoleum hammer finish but do not have any equipment. Can you recommend an inexpensive HVLP system for home/light use?
A: Yes, but I’d advise against buying a spray system just for this one job. You can buy Rustoleum hammer finish in aerosol cans under the Universal label. http://www.rustoleum.com/CBGProduct.asp?pid=180
Those Universal cans are comfortable, spray beautifully with a built in trigger, and will spray in any direction, including upside down. Buying a few cans of aerosol will be vastly cheaper than buying a spray rig.
However, if you are set on buying spray equipment, decide first all the various things you plan to use it for and base the purchase on that. You know from years of hearing it from both me and your father that buying cheap tools, including those inexpensive because they will only do one job well, is rarely a good investment. If you really want to buy a spray rig, call me and I will walk you through the process.

Cleanliness is next to…

Michael — Mon, 16 Aug 2010 17:12:58 +0000

Q: In preparation for painting stripped metal furniture, we’ve wiped down the pieces with soapy water and wiped everything dry, gone back over the pieces and have given them a light sanding. Do I need to be concerned with chemical residue from the previous finishes, stripper or other contaminate?
A: Possibly. Some strippers contain wax, and unless you remove it, you could have problems. Ditto for any soap residue. Once you have removed all the soap residue, which comes off with clean water, wipe the pieces with mineral spirits to remove any possible wax. Other than that, you have little to worry about.

What hath iron wrought?

Michael — Fri, 13 Aug 2010 14:00:28 +0000

Q: We purchased a used dinette set; the style is often referred to a wrought iron, however the chairs and base are clearly metal. They appear to have been originally powder coated, and subsequently painted over by the former owner with what looks like latex paint. Using a gel stripper and a bit of elbow grease we’ve managed to strip all the chairs and the table base down to bare metal. However, there are a few crevices that we could not reach and remove the original paint. We’ve gone as deep as we could, using a variety of wire brushes. Will these areas create a problem for the new finish?
A: Possibly. You could get bridging. The ideal way to remove the finish from crevices in metal is by sand blasting or even better, soda blasting.

Fume a beam?

Michael — Tue, 10 Aug 2010 14:00:41 +0000

Q: I want to fume the ridge beam in my house. Obviously, I can’t simply remove it, and place it in a tent for fuming. What would happen if I painted a light layer of ammonia on it?
A: First, fuming only works with woods high in tannin, so before you do anything, figure out what type of wood it is and whether it is one that is high in tannin or not. Second, fuming uses ammonia fumes, which is pure, concentrated ammonia. Once it is in liquid form it is ammonium hydroxide, which will color wood, but not in the same way as fuming. It tends to be less effective and yields a different color which is not surprising when you remember that you are no longer using pure ammonia, which is a gas, but rather a compound of ammonia and water. Even at best, fuming is a bit of a crap shoot. What color you get and how much impact the ammonia will have depends on the type of wood and, in this case, the concentration of ammonium hydroxide. For example, household cleaning ammonia is usually only about a 5% solution, and is a weak chemical stain at best. Ammonia from a blueprint machine is typically a 26% solution, and while more effective, is both dangerous and noisome to use. Finally, chemical stains, which is what ammonia is, only work on clean, raw, sanded wood. Call me a skeptic but I doubt that’s a good description of any ridge beam unless it is brand new and recently sanded. In short, I think it is a very bad idea for a wealth of reasons. Why not simply stain it the color you want it to be?

Just a shmear

Michael — Fri, 06 Aug 2010 14:00:59 +0000

Q: If I brush on a final finish, will it cause water based dye stain to bleed into the finish on the brush and smear?
A: Water soluble dye can bleed onto a brush loaded with waterbased finish. Whether that will be enough to smear the stain also depends on your brushing technique and how aggressively you wiped the dye originally. It is also worth noting that some dye stains contain a binder that will prevent this. Others don’t.

Cleanup in aisle two

Michael — Thu, 29 Jul 2010 14:00:40 +0000

Q: I’m using a water based urethane acrylic lacquer. Can I leave the stuff it in the spray gun (HVLP) in between coats, or do I have to clean the gun every time?
A: Most waterbased finish clog gun tips sooner than you would expect, and cleaning the gun can be very troublesome if the finish does set up in it. I prefer to empty the gun and at least blow clean water through it right after spraying. It’s fast, cheap and is good insurance. I’d do a more thorough cleaning once you are done spraying for the day.