Shellac: The Mighty Sealer

Wednesday's What does it mean furniture paint glossary written on teal background laminate and veneer

Today’s Wednesday’s What Does It Mean is a single entry: shellac.  There were supposed to be two others, varnish and lacquer, but there is a lot I wanted to share about shellac, in addition to its definition.  I decided to give you more than you ever wanted to know about this useful product, but, first, I will give your the definition.

Shellac is a natural product that is produced from the resin of the female lac bug.  It  is used for finishes on antique wood furniture and as a sealer when working with furniture that is being refinished.

lac bug shellac

By Harold Maxwell-Lefroy –, CC0,

Now that we have that pesky definition out of the way, let me tell you a bit more about shellac and why you want a can of it in your tool box.  I am going to glaze over the use of shellac as a finish.  I will focus more on its use as a sealer.  It is a mighty sealer!  When working with furniture that you have no freakin idea of what the piece of furniture has been subjected to in the past, shellac may be your best defense.

Okay, a little bit of shellac history may help put it all in perspective for you.  Back in the 18th century (that is the 1700’s for those who don’t like to do the math) a wax finish was very often used as the finish on wood furniture. As almost anyone who has ever rubbed their hand over a {properly} waxed piece of furniture, knows it feels oh-so-good.   Devine is not too mighty of a word to describe that feel.  The problem was, that wax, exclusively, used as a finish on raw wood is not the most durable finish.  (Hold your britches – I’ll get around to that in another post.) So, in the 1700’s, while wax was used a lot for wood finishes, in the 1800’s, they realized that you could put shellac OVER wax and have a more durable finish.  You should always remove as much of the wax as possible, before using shellac

pizza box shellac

Greasy pizza boxes are a no-no on any furniture!

Side note – I guess those charged with housekeeping duties way back when, in the 1800’s, also had issues with other household members not using coasters and hot pads or at least putting something under that hot, greasy pizza box.  Some things never change.





So, what happened in the 1800’s was they began putting shellac over the original wax finish.  It was better than its only-wax predecessor.   In the early 1900’s, it fell out of favor and was replaced by lacquer. Compared to products available in today’s world, shellac is only moderately durable.  Shellac then, and today, as a finish, has some shortcomings: it scratches easily, it blushes in humid environments, it has poor resistance to acids, alkalis, solvents and heat.  It does make a beautiful finish when applied in the “French Polish” method.  Today, it is generally only used, as a finish, on restored antiques to replicate the original finish.

Where shellac shines is as use as a wood sealer.   It is used to prevent substances in the wood from migrating into the paint or finish that is being applied.  It will seal in waxes and oils, including silicone oils from furniture polishes.  It also blocks resins from pine knots from seeping and blocks odors, such as smoke and animal urine.  In our niche of furniture painting, it is most often used to prevent tannins from bleeding through the paint.  Often with vintage 1930-1940’s mahogany and cherry pieces, you get the dreaded red bleed.  You are never quite sure if it is tannins or the dyes that were frequently used in the stains of that period. Either way, the shellac prevents the bleed.  Tannin bleed can occur when you apply the paint and when you apply a water-based top coat.  That means just because you don’t get bleed when you apply your paint that you are out of the danger zone.  If working on a project that will have a crisp, light color of paint, a couple coats of shellac is a good insurance policy to invest in.

  • Prevents migration or unwanted substances from out of the wood and into your paint/finish  layer
  • Blocks the seepage of pine resin from knots
  • Seals in waxes and oils that may have been applied to the surface of a piece of furniture
  • Prevents tannin and stain bleed
  • Blocks smoke, urine, and other unwanted odors

Do you know you can make your own liquid shellac?  You can by using shellac flakes and denatured alcohol.  I am not going to venture into that process here.  There are plenty of tutorials available that you can find on line and in wood working books.

Since most of us are not going to make our own, when buying shellac you have four options.  All of them are Zinsser® products.  Zinsser Bulls Eye® pretty much has a monopoly on ready-to-use shellac.  What you will find at your local hardware store is waxed shellac in liquid form in (1) clear, (2) amber, in clear in a (3) spray can.  The (4th) product is a liquid packaged by Zinsser as SealCoat®.  It is the unwaxed form. It is my preferred shellac product, although I have to order it online.

the four types of readily available shellac

Four Types of ready-to-use Shellac

SealCoat differs from the the waxed shellac in four ways.  First, as expected, the wax that makes up about 5% of the lac, has been removed.  Secondly, it is what is referred to as a 2 pound cut.  The waxed liquid variety is a 3 pound cut.  The pound cut refers to the number of pounds of shellac that is dissolved in the alcohol.  The 3 pound cut is a thicker consistency.  I personally prefer working with the less viscous product. It is easier to apply with a brush.  You get fewer brush marks.  It dries very quickly and applying it can be tricky.  You want to lay it down and not over work it.  It starts setting up (getting tacky) immediately and that is when the brush strokes get formed, if you keep brushing it as it is drying.  You can thin shellac with denatured alcohol.  The third difference is the shelf life.  Shellac has a shorter shelf life that many of today’s products.   I have tried to find what the actual shelf life of shellac is, but like most things in life, there seems to be many opinions on that issue. However, longer the shellac has been in its dissolved state the slower it dries and the less hard and water resistant it becomes.  The unwaxed variety has a longer shelf life.   I only buy a quarts worth at a time to make sure I don’t run into a problem. The fourth difference is it can be used as a pre-stain conditioner.By mixing equal parts unwaxed shellac and denatured alcohol you have a product to use before staining, on soft woods that tend to be blotchy when stained.

The first difference between waxed and unwaxed shellac, the lack of the wax, needs more explanation.  Shellac with wax is slightly less transparent and slightly less water resistant, not something that when using it as a sealer, we are concerned about.  Waxed shellac has been known to interfere with proper bonding of water-based finishes and varnish.  I have not experienced that, because, I believe, I am always putting paint over the shellac.    Also, worth noting, Zinsser points out in their technical information, that you should not use TSP to clean your furniture if you are using the waxed shellac.

You can find the Technical Data Sheet for shellac HERE and for SealCoat HERE.   SealCoat, Zinsser, Bulls Eye are all registered trademarks of the Rust-oleum and are not affiliated with CeCe Caldwell’s Paints in any way.

In our next Wednesday’s What Does It Mean, we will cover varnish and lacquer and why the three words are not interchangeable.