Monday, October 31, 2011

Important Shellac Information

About Shellac
Shellac is an excellent quick drying non-waterproof Child-Safe finish. Flake form allows fresh shellac to be prepared and avoids waste. Use shellac to seal in sap, resin, grease or oil marks after cleaning and prior to painting or lacquering.

Thinned shellac (1/2 to 3/4 pound cut) makes an excellent stain barrier coat or hold out coat especially on soft woods and difficult or end grain prior to using a pigmented stain.

Dissolving & Mixing Flake Shellac
Mix what will be used within 3-6 months. Mix in a dark plastic or glass container with a tightly fitting lid. Soak the flake shellac in about 1/2 of the total alcohol to be used for 24 hours or longer (cool room temperatures will slow the process; pulverize button shellac to speed dissolving) stir occasionally and when dissolved add the balance of the alcohol. The consistency of shellac is designed by "cut". A 2 pound cut is two pounds of shellac flake in one gallon (or 1/2 pound shellac in one quart) BEHKOL Denatured Alcohol.

For first experiences with shellac it is recommended that you start with a light consistency, preferably about a 1 pound - 1.5 pound cut. A one pound cut is (1 pound of flake to 1 gallon) or (1/4 pound in a quart) of Denatured Alcohol.

To mix 1 pint of 1 pound cut liquid shellac use approximately a 2:16 ratio of shellac flakes to alcohol (2 ounce of shellac flakes dissolved in 16 ounce of alcohol). Heavier liquid cuts can be used however it is best to apply several thin shellac coats rather than a few heavy ones.

After the shellac is fully dissolved, it should be strained through fine mesh cheesecloth to remove any impurities. Shellac is made from the lac bug and a few bits of bug carcass or packaging are often left in the dry shellac resin. Before the liquid shellac is used, it should be stirred thoroughly.

Different shellacs may be intermixed in the liquid state to adjust color tone or shades.

Shellac Application
When used as an under-coater prior to other finishes, use a Dewaxed shellac. Shellac should be applied in long strokes with the grain. Shellac requires some practice in order to be used to its full potential. Dip a good natural bristle brush about half way into the shellac and gently clear excess shellac against the side of the container, this gives a reasonably filled brush for full strokes without incorporating air in the shellac. Allow each coat to dry thoroughly. Shellac should be sanded as necessary between coats.

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 and the paper will clog. After sanding, wipe the piece thoroughly with a tack cloth and recoat. Depending upon temperature and humidity conditions, allow from two to six hours drying for each coat. Some craftsmen prefer to do their finish sanding on raw wood after first giving it a coat of shellac as this stiffens the wood fibers and allows any rough portions to be easily sanded.

When thoroughly cured the finish can be rubbed out with oil free & long stranded #0000 Steel Wool or fine pumice with paraffin oil. Rubbing should always be done with the grain. 24 hours after the final rubbing, to protect your shellac finish, apply a thin coat of paste wax. Allow the wax to dry completely and buff with a soft cotton cloth.

Store mixed shellac: tightly sealed & cool, and in a dark place if a clear container is used.
Store Flake: tightly sealed, cool, and dark.
Test all older shellac mixtures (if several months old) for drying. If the surface stays tacky after 8 hours and does not sand freely without gumming, the shellac is old and will not cure hard and must be discarded.

"Packing" or "Blocking"
Dewaxed shellac flake when exposed to high heat and/or humidity tends to "block" or pack together in small, or occasionally, large chunks or "blocks". To avoid blocking: store shellac flake tightly sealed in a cool, dry location (under 70°F).

NOTE: Blocking is not detrimental to the shellac flake.

If the flake blocks, wrap larger chunks in cloth or thick plastic sheeting, to keep them from flying all over the room, and reduce them to manageable size with a hammer or dead blow mallet.

The finest flakes are imported via air to avoid blocking however there is little control if the product is delayed in a delivery van or air container on a hot day.

More Shellac Guidelines
Use Behlen BEHKOL™ or a high-test denatured alcohol (10% denaturants or less).

If the label does not say, the MSDS sheet for the brand will have the mixture percentages. A 190 proof denatured alcohol has 5% denaturant.

  • A warm environment will aid the alcohol in dissolving flake. NEVER place alcohol or shellac on or near any source of heat. In a cooler room, set the lidded bottle of dissolving shellac flake in a container of hot (not boiling) water to aid in dissolving.
  • Strain the working shellac solution through layers of cloth to remove any particles of dirt or organic material.
  • Evaluate flake color when in liquid, variation in flake thickness from production batches can make a thinner flake look lighter in tone. Slight seasonal variations do occur in a natural product but they will be within the laboratory acceptable color range.
  • Blending Flake Colors or Tones: Any of the shellacs may be intermixed or inter-layered. For repeatable results, blend shellac colors only in liquid form.