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Shellac

Shellac as a Woodworking Finish

What it is

The form of shellac used by woodworkers as a finish is formed by dissolving flakes of shellac in an alcohol solvent. This shellac and alcohol mixture is then applied to the workpiece by the use of a rag. The origin of the flakes is actually the secretions of the female lac bug (Laccifer lacca, formerly the Coccus lacca), left on the banyan tree but sometimes on other types of tree, found in the forests of Assam and Thailand. Once these secretions are removed from the tree, it is called "seedlac". The harvesting process leaves many impurities in the seedlac, and therefore it must be processed, resulting in a dry flaky substance.

These shellac flakes take on a range of colours orange to nearly transparent 'white' shellac (produced by bleaching orange shellac). Shellac is also available in waxed (natural) and dewaxed formulations.

When to consider it

Shellac is somewhat outdated or obsolete when compared to most other modern finishes, as it provides only minimal protection. It is, however, a very useful primer finish since many other finishes bond very well with it.

Shellac is used in the "french polish" technique of finishing, and therefore any project striving to create or restore a french polish finish would require its use.

Craftsmen desiring a food-safe finish should also consider shellac since it is entierly foodsafe if the correct solvent is used.

As far as appearance is concerned, shellac is suitable for virtually all wood types, from pine and cherry, all the way to imported exotics and tropical woods.

Advantages

As long as the surface bearing the shellac has not been damaged, shellac provides the following benefits:

  • Water resistant
  • Resistant to alcohol
  • Excellent as a primer coat, to seal and prevent the bleeding of resin or pigments, and to prevent wood stains from blotching
  • Can be applied under most other finishes. Note that polyurethanes have trouble adhering properly due to natural shellac's wax content. Simply use de-waxed shellac to prevent these problems.
  • Easy to repair
  • Easy to apply (brush, rag, or spray on, thin cuts easiest)
  • Easy to re-apply if the original finish becomes worn or damaged
  • Non-toxic and food-safe (Use appropriate solvent)
  • User can control how quickly product is built-up by adjusting dissolved shellac concentration
  • Cold temperature application – Unlike other finishes, shellac can be applied in cold temperatures (5 °C/40° F and below) without concern over proper drying and curing
  • Non-yellowing and non-darkening as it ages

Disadvantages

  • Easily damaged by alcohol (it dissolves the finish)
  • Rare cases of allergic reaction (skin rash) during application
  • Once mixed with alcohol, shellac has a limited shelf-life of approximately 6 months. Use of mixed shellac that has begun to polymerize may suffer from never successfully drying!

Variations

Shellac Flakes

Shellac is primarily sold as flakes, and the woodworker must prepare the quantity required by dissolving the shellac flakes in alcohol. The color of a package of dry shellac indicates the degree of refinement the shellac flakes have undergone. Shellac, in its raw state, is a dark orange-brown color, which becomes lighter in the process of refinement.

Button shellac (button-lac), the least refined, is so named because it is in the form of dark brown buttons. It is suitable for use only when a very dark finish is desired.

Orange shellac, a more refined grade, is also recommended for darker finishes, but it allows more of the underlying wood to show through than does the button shellac.

Blonde shellac is a pale amber color. It imparts little change to the color of the finish.

White shellac has had all its natural pigment bleached out, and is quite clear. It is recommended for a very light-coloured finish.

These variations are not limited to the above, as the refinement process can be tailored by any manufacturer.

Each of these basic types are also available in de-waxed form, containing less than their natural 2% to 4% wax content.

Shellac Liquid (pre-prepared)

Sometimes called "French Polish" or prepared shellac, this is essentially shellac flakes pre-dissolved in alcohol (sometimes with an oil or other additive) to eliminate the mixing step. These products are beneficial, however they have a limited shelf life.

How to use it

As with any traditional product that has been used for many years, there will be many different opinions on how to use the product. What I will present here is the most simple and straightforward technique, and I will identify optional steps as such.

Precautions

Be careful with the handling and disposal of the rags used to apply shellac. The shellac itself is not a problem, however the alcohol used to dissolve the shellac is extremely flamable, and the even the vapors produced by the drying and evaporating shellac are flammable. and combustible. Allow rags to thoroughly dry on a non-flammable surface (such as a concrete block), or washed, or soaked with water before placing in the garbage.

Keep out of reach of children. The alcohol used is usually denatured alcohol, (making it somewhat umpleasant to drink), but some children are apt to investigate...

Wear a dust mask when sanding between coats. Fine dust is a woodworker's hidden health hazard.

Preparation

Shellac has two primary uses in woodworking. First it can be applied as a sealer under some other type of finish, or it can be used as the final finish on the project. The only real difference is the number of coats that are applied, since the sealer coat does not need to be thick (other products will offer physical protection) while the finish coat needs to be thick enough to protect from physical abuse and the elements.

Ensure the surface is adequately prepared by sanding using progressively finer sandpaper until you reach 220 grit (or optionally 320-dry grit) sandpaper. This will leave the surface smooth and there should be no visible scratch marks that remain. If the final finish is to be some sort of paint, 120/150 grit is all that is required, since the paint will cover any imperfections that will remain, and you just waste money and your precious time sanding with no visible benefit.

Of course, if the shellac is being applied over some other finish, such as oil, perform the sanding steps before applying the oil.

Preparing The Cut

If you are using a pre-mixed shellac product, you can safely ignore this section.

Shellac flakes must first be dissolved with alcohol (cut with alcohol). The dissolved shellac is referred to by its concentration. Therefore, a 1-lb cut of shellac has 1 pound of shellac flakes dissolved in 1 gallon of alcohol. a 1-lb cut of shellac has 2 pounds of shellac flakes dissolved in 1 gallon of alcohol, and so on.

Cutlb/galoz1/qtg/L
(metric)
Use
1-lb.14120Pre-stain sealing, French Polish finishing
2-lb.28240Pre-finish sealing; general wood finishing
3-lb.312360Floor finishing; sealing knots & sap streaks
4-lb.416480Sealing tough knots & sap streaks, stains2
1 The oz listed is ounces of weight. Use your scale, not the measuring cup for this!
2 The 4-lb. cut is generally used by professionals, and is considered difficult to work with by most hobbyists.                  

Beginners and those unsure of the outcome are strongly advised to use a 2-lb or smaller cut. Even I prefer to apply two coats of a 1 1/2-lb cut, since I find the 2-lb cut asks for less hesitation, and is not as easy to apply on highly figured workpieces. But if your workpiece has large clear surfaces, the 2-lb or 2 1/2-lb cut may save you alot of time since you won't need to mess with many corners.

To produce a cut, you need a scale to weigh your shellac, a measuring cup (of whatever size you find appropriate), and a glass jar with a tight fitting lid that large enough to hold the quantity of shellac you intend to make. Since the measuring cup will only be used for denatured alcohol, it is safe to use a kitchen measuring cup and simply wash it afterwards.

Metal cans should not be used as the shellac will react with the metal, darkening the shellac.

You will often require less than a galon to finish a project. One liter/quart of a 1 1/2 cut is enough to apply three or more coats to a pair of bedside tables and drawers. Remember to only make as much as you think you will use. It is quick and easy to make more shellac, but is expensive and wasteful to make too much and throw it away.

If you have an accurate kitchen digital scale ($20 at most department stores), the easiest method to proceed is to measure your alcohol and place it in your glass container. Place this container on the digital scale and reset/zero the scale. Now you can add shellac flakes directly to the container until the scale reading reads your desired cut weight. Note that if you take too long adding the shellac flakes, some scales go to sleep/turn off and you will not be able to tell how much shellac you have already added!

Another method is to weigh the shellac flakes separately, measure out the alcohol, then add the flakes. Both methods work fine, but this method requires you to clean the container that you measured the shellac flakes in.

After mixing the shellac flakes, it takes up to 24 hours to dissolve. Seal the container and let it sit overnight, occasionally mixing/shaking the jar.

Do not be concerned about being overly accurate. The difference between a 1-lb cut and a 1 1/2-lb cut is not overly significant, and it is easy to correct by just adding some more alcohol if desired. Once you start applying the shellac and seeing how it dries, you can always adjust your shellac for the next coats.

After the shellac is fully dissolved, it should be strained through a fine-mesh cheesecloth before use to remove any impurities. Shellac is made from the secretions of the lac insect and a few bits of insect carcass are often left in the shellac flakes.

Shelf Life

Shellac that has been cut with alcohol undergoes a chemical change making it take longer and longer to dry. If the shellac is applied once it has started to undergo this process, the finish that it produces will be softer and will be more prone to water damage and scratches. Also, exposing the pre-mixed shellac to heat will accelerate this process, so keep the prepared shellac in a cool (less than 24 °C/75 °F), dark location, in a tightly sealed container (mason jars work great). Since shellac is dissolved in alcohol, there is no worry about cold weather unless you think it will be exposed to temperatures near −114 °C (-173 °F)...

Application

Tools

Shellac can be successfully applied using a rag, brush, or sprayer. If you plan on using a brush, I suggest you keep to a 2-lb or less cut of shellac, or keep a close eye out for brush marks drying into your project that you will have to sand out if you want a smooth finish.

Techniques

Before shellac in the liquid state is used, it should be shaken or stirred thoroughly and allowed to stand for a few hours.

If using a brush, shellac should be applied using long strokes in the direction of the grain. A good-quality brush with a chisel tip should be used. Its bristles should be dipped about 3/4 of the way into the shellac and gently cleared of excess shellac against the rim of the container. This gives a reasonably full brush for full strokes without incorporating any air in the shellac. Place lid on the jar to reduce the evaporation in the jar.

If using a rag, fold the lint-free cloth in such a way that you have multiple layers of cloth (allowing the cloth to hold more shellac), but make sure the bottom layer that you run across the workpiece is smooth and not creased or wrinkled, as it may leave marks on your project.

If using a conventional, HVLP or airless spray system, use a 2-lb or thinner cut. For convntional and HVLP sprayers use the same pressure and tip size as used for lacquer or consult manufacturer’s operation guide. For airless sprayers, use a .011 to .013 tip and 800 to 1000 psi. For all sprayers, apply shellac evenly to the surface in thin, overlapping passes.

Shellac should be sanded between coats and each coat should be allowed to dry thoroughly. If the shellac is dry, sanding will produce a fine powder on the surface. If the shellac is not dry, it will be somewhat tacky to sand and the paper will clog. If your project has complex shapes, you may find that 000 or 0000 steel wool gives you adequate sanding without fall the fussing with delicately folding sandpaper. After sanding, the piece should be wiped thoroughly with a tack cloth and recoated. Depending upon temperature and humidity conditions, you should allow between two          and four hours for each coat to dry. Some craftsmen prefer to do their finish sanding of the raw wood after first giving it a coat of shellac, since this stiffens the wood fibers and allows any rough portions to be fully sanded off.

Projects should receive at least two coats, and thinner cuts of shellac will require more coats to build up the same level of protection.

After the desired number of coats have been applied, the finish can be rubbed with 0000 steel wool or FFF pumice with paraffin oil. Rubbing should always be done with the grain. If it is desired, a coat of paste wax can be applied 24 hours after the final rubbing and the surface buffed to a finish.

Repairs

Repairs for shellac couldn't be simpler. Shellac has the wonderful benefit that each layer of shellac that you apply softens the previous layer, and the two layers essentially bond together.

If a wax has been used on top of the shellac, make sure to remove the wax first.

Simply prepare some shellac (don't forget that shellac has a limited shelf life), then brush or wipe on one or more coats using the techniques described above. If you are simply filling in a scratch, refinishing the entire surface is not necessary, and you can use a fine brush to target your application of the shellac. Just be careful that your sanding step does not cut through the surrounding shellac. In these cases, a lighter cut usually produces a smoother finish without the need for sanding since the shellac has a better chance to self-level before drying. The only downside to this is that you must use more coats to develop the same level of protection, but for some that is a reasonable tradeoff.

Important tip from the Experts– If you know your piece of furniture is truly an antique and still has its original shellac finish think carefully before refinishing. The value of an antique increases tremendously if it still has its original finish. If the finish is badly worn or damaged bring it to a professional furniture refinisher.

Removal

You can remove the majority of shellac by using ethyl alcohol (or any other appropriate solvent) and rubbing the surface. The solvent will soften the shellac, and you need to wipe away the softened shellac. If the shellac was applied on top of an oiled wood (such as linseed or tung), the shellac should be possible to remove completely. If the shellac was applied directly on fresh wood, the shellac would have been absorbed into the fibre of the wood, and may not be removed completely without sanding. This is usually considered a benefit of shellac, but in this case it makes removal difficult.

Where to get it

Pre-mixed shellac is available at most big-box construction stores, and the flakes are slightly harder to track down because of their limited popularity.

Lee Valley Tools - Shellac
Lee Valley Tools - Solvent / Thinner

Cleanup

Please see the Precautions section above for appropriate disposal of rags used to apply shellac.

Shellac is dissolved in alcohol, and alcohol such as ethanol and isobutyl alcohol are ideal for cleanup, or as a solvent for the preparation of shellac.

References

Wikipedia - Shellac
Zinsser - Shellac brushing instructions (also a vendor)
FDA application (and approval) of orange shellac as "made with organic" food coating
Excerpt from US FSIS USDA report suggesting shellac is generally regarded as safe (GRAS): "Drying agents and diluents that are generally recognized as safe (GRAS) – Title 21 Section 73.1. Specifically, may use water, dextrose (corn sugar), isopropyl alcohol, ethyl alcohol, shellac, and acetone."
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