Michael Dresdner » shellac

Don’t make me blush

Michael — Wed, 01 Dec 2010 14:00:56 +0000

Q: I need to finish a reproduction 17th Century Chester County Spice box. How much trouble will I have if I take the box into the unheated garage long enough to spray shellac with an HVLP and, then take it right back into the house? Will I end up with blushing?
A: Not likely. However, if you do, simply spray it again and the blush will go away. The truth is that you probably will have no problems whatsoever.

Play musty for me

Michael — Tue, 30 Nov 2010 14:00:27 +0000

Q: My old desk has a kind of musty smell. Can this be improved by treating the wood?
A: Musty smells can come from mildew or accumulations of dust and dirt. Clean the desk, including the interior areas, and kill any mildew with laundry bleach. If you want, you can seal the exposed wood areas, such as the unfinished drawer sides and cabinet interiors, with a coat of shellac, and that will nicely block any smells.

Formaldehyde

Michael — Mon, 29 Nov 2010 14:00:10 +0000

Q: I purchased a 70s-era desk with an oak veneer. Much of the desk is constructed of heavy fiberboard. I’m worried about the formaldehyde and other chemicals off gassing. Is there a way to seal the exposed fiberboard?
A: If it is from the 70s, anything that was going to off-gas has long ago done so, but to answer your question, any film forming finish will seal in formaldehyde. That includes shellac, lacquer, oil varnish, and both oil and waterbased polyurethane.

Circa 1920

Michael — Wed, 10 Nov 2010 14:00:19 +0000

Q: I have a circa 1920 chiffarobe I would like to refinish. I stripped it with alcohol and sanded to 220. I have never been very successful with shellac. What would you suggest for a finish what would give a reasonable look and protection?
A: What I would suggest is what it had originally, and if the finish came off with alcohol, that pretty much confirms it was shellac. Since you have, as you say, never been very successful with it, you have three obvious choices; learn to use it (it’s actually a very easy finish to use, if someone shows you the ropes), take it to someone else to finish, or apply a non-original finish. If you choose a non-original finish, it should, of course, be any finish you do have success with. In case you were concerned with period authenticity, the other finishes in common use for furniture in the 1920’s were oil varnishes and nitrocellulose lacquer.

Inked salad bowls

Michael — Fri, 29 Oct 2010 14:00:31 +0000

Q: I want to color walnut sapwood on salad bowls with India ink, then seal it with shellac and salad bowl finish. Would this be safe for food?
A: Yep. By the way, I would let the ink dry then go straight to salad bowl finish. In this case, adding shellac would weaken the finish.

Epoxy over shellac

Michael — Fri, 27 Aug 2010 14:00:02 +0000

Q: Can epoxy go over shellac?
A: It depends on the epoxy. Most contain either alcohols or amines, either of which will bond to shellac, but because epoxy formulas can vary so widely, it would be best to either know more about the formulation you are using, or do a sample followed by a cross hatch adhesion test.

Misguided advice?

Michael — Mon, 12 Jul 2010 18:10:13 +0000

Q: I am finishing some beech and used Zinsser SealCoat in a 50-50 mix with denatured alcohol. After light sanding I applied tung oil but the result was some serious blotching. I’m planning on using shellac as a finish.
A: Zinsser SealCoat is pure, dewaxed shellac, already reduced to exactly the right consistency. That implies two things. First, there is absolutely no reason to thin it when using it as a sealer coat. In fact, thinning it that much turns it from an almost perfect sealer into something almost completely useless. Second, all you need do for a shellac finish is continue to apply coats of SealCoat until you are happy with the results. It’s a very simple and very effective finish. I don’t know what possessed you to put tung oil on wood you want to finish in shellac – perhaps some misguided internet chatter – but as you now know, doing that was both pointless and problematic.

The evils of over sanding

Michael — Fri, 11 Jun 2010 14:00:30 +0000

Q: I’m getting some shiny areas in the finish after four coats of satin lacquer, scuffing with 180 in between. The sealer over the pore filler is two coats of tinted garnet shellac. Over that is one coat of sanding sealer. I fear I’ve sanded through the lacquer and gotten down to either the tinted shellac or the sanding sealer during my scuffs and that’s why I’m getting these shiny spots. A: It’s possible. Scuffing means sanding very lightly with 320 or 400 paper, not 180, which is coarse enough to cut entirely through the finish. Incidentally, there is absolutely no reason to scuff between coats of evaporative finishes like shellac or lacquer, since both dissolve the prior coat. The only reason to sand is to remove dust nibs or if you leave brush or spray marks in the finish, and even then you can usually wait until just before the final coat with evaporative finishes. It is also both unnecessary and counterproductive to apply both shellac and sanding sealer. Use one or the other as a sealer; preferably dewaxed shellac. In many cases, neither is needed. For now, stop sanding between coats, add two more coats of satin lacquer, then let the finish cure fully and rub it out to get a uniform sheen.
If I may be so bold, from the tone of your questions I’d say you need to learn some more finishing basics. Therefore, I’d suggest you read The New Wood Finishing Book, which is set up as a comprehensive step by step course in finishing. You can find it on my book and video page. It will give you a good grounding in finishing and help you avoid both unnecessary steps and errors.

Matching Martin

Michael — Tue, 08 Jun 2010 14:00:05 +0000

Q: I’m restoring a Martin guitar, and after staining, I added three very
light wash coats of 1lb. cut shellac. I’d like to strike the pores black
with Finishers Glaze seal with sanding sealer, fill pores with Bartley’s dark, seal and topcoat. Martin mahogany pores are darkened nicely. I’m trying to do it the right way.
A: I’m afraid you are doing it the hard way. The easy way is to stain the wood, preferably with water soluble dye, seal with one thin coat of SealCoat or dewaxed shellac, then fill the pores with a dark pore filler. There is no glaze on Martin guitars, and many were stained and filled in one step, on the raw wood, with staining pore filler. Keep it simple and you will have better results.

Apples to apples?

Michael — Fri, 04 Jun 2010 14:00:10 +0000

Q: We want to do a comparison of the performance of a variety of solvents for shellac:Lee Valley’s Shellac/Lacquer Thinner; a lab grade of denatured ethanol and common hardware store methyl hydrate. We plan to prepare samples of blond shellac, mixed in each of the three solvents, apply them to wood samples and test the resulting finishes. I’m looking for information on what kind of tests are used in the industry to evaluate the performance of shellac finishes. I’m interested in time required to recoat, sanding ability, and final resistance to abrasion and liquids.
A: Pure methanol (what you call methyl hydrate) is considered the traditionally ideal solvent for shellac. However, because it is so dangerous, vastly safer ethanol has long been used, and is used almost exclusively here in the US. Fortunately, the difference between the two as a shellac solvent is almost indistinguishable.
Which alcohol you use, and whether you use pure alcohol or a mixture of alcohol and other solvents, will determine how fast the flakes dissolve, with pure ethanol and methanol being the fastest. In addition, higher molecular weight alcohols, such as propanol and butanol, will require more solvent per resin weight. As a result, adding a given amount of shellac resin to the same volume of, say, ethanol and butanol, with result in the butanol dissolving slower, and will also result in the butanol yielding a slightly thicker, more viscous mixture.
Drying time will be determined by the evaporation rate of the solvent. Again, ethanol evaporates substantially faster than butanol.
As for the final finish; if the shellac resin is given enough alcohol, whether in mixture or alone, so that it can be fully dissolved, and if the mixture is given sufficient time to dry, which of course will vary with the solvent evaporation rate, the eventual film formed will be the same. That’s because once the solvent evaporates, you are left with pure shellac resin in a thin film on the wood. In terms of ultimate durability, how that film of resin got there or how long it took to dry are of no consequence. Thus, a test of the final finish will give the same durability and sandability, though recoat time will depend on the solvent evaporation rate.
By the way, if you add oil to your French polish pad, that, unlike the solvent choice, does indeed alter the final film. Most oils make the shellac film less brittle, weaker and more prone to water spots.