Seeing its market disappearing, Zinsser Bulls Eye , with the help of some woodworking writers, turned shellac into a sealer, even introducing a dewaxed variety SealCoat that was marketed for use under polyurethane.
But here we return to the central question: Why not use polyurethane itself as the sealer? Why use shellac under several coats of polyurethane — or under any other finish?
The answer is to solve a problem. Shellac has wonderful blocking properties, better than any other finish. It blocks silicone contamination, which causes fish eye, odors for example, from smoke or animal urine , and residual wax extremely well. Shellac also blocks the resin from pine knots and very oily exotic woods, which can slow the drying of lacquer and varnish significantly.
But notice that the first three situations are all refinishing problems, not new-wood problems, and the last is rare for professional finishers. Not only is there no benefit to using shellac as a sealer in most situations, there are good reasons not to use it.
Shellac is a difficult finish or sealer to use. The first reason is the confused naming. Before you even get started, you have to learn the different types of shellac. In liquid form there are clear actually pale yellow and amber shellacs. Should you be using that?
Or will the shellac with its natural wax still included work just as well? In flake form, which you dissolve yourself in denatured alcohol, there are many more varieties: blonde, superblonde, lemon-yellow, orange, garnet, button, ruby, extra dark and more.
These names all refer to the color, ranging from pale yellow to very dark orange. A second issue is the way solids content is measured. Clear and amber liquid shellacs are three-pound cut.
Dewaxed SealCoat is two-pound cut, which is no longer listed on the label. Though conversion to percent solids is possible so you can predict the total build of your finish , this is another difficulty you have to overcome. A third issue is shelf life. Once shellac is dissolved in alcohol, it begins deteriorating more rapidly in hot temperatures. Shellac, on the other hand, when dried, dissolves readily once it is moistened with alcohol, fresh shellac or lacquer thinner.
Is Shellac more durable than polyurethane? It is extremely durable and one of the hardest of the topcoat finishes. It is stronger and better wearing than shellac and varnish. Debatable as to whether or not it's harder and more durable than polyurethane.
Is lacquer more durable than polyurethane? Unlike the lacquer finish, polyurethane does not penetrate the wood. It only gives a surface coat that is durable.
The other downside is that the oil-based one can leave a yellowish color on light wood products. Because of its thickness, polyurethane is rarely applied with the spray unless a thinner is added to it. Which is better shellac or varnish? Dried shellac, on the other hand, dissolves readily when moistened with alcohol, lacquer thinner or fresh shellac.
A varnish coating is typically heavier than shellac, and usually only one or two coats need to be applied. A completed shellac finish is typically smoother than varnish, albeit somewhat more brittle. How long does Polyurethane take to cure?
Length of time to dry for water based polyurethane: After 2 days, you can move furniture back. It takes a full 30 days for the floors to cure, so it's ideal to wait 30 days before putting area rugs on the surface. If you want to put area rugs back sooner, than 2 weeks is another good benchmark.
Which is better varnish or polyurethane? While polyurethane is water- or oil-based plastic resin, varnish is older and made from resins, oils, and solvents.
Because of the higher ratio of solids, varnish is less susceptible to ultraviolet light damage. This finish gives a more tinted color when applied and requires more coats than polyurethane. What is the difference between polyurethane shellac and lacquer? So basically, shellac will seal the wet wood better than the varnish? Is there anything I can mix with the shellac to make it more flexible, so it can better withstand shrinkage?
Shellac is usually used under varnish if dewaxed or by itself. With a light coat, you should be OK Sponsored Forums Private Forums Authors. Replies: 12 Last Post: , AM. Replies: 8 Last Post: , AM. By Helen Gee in forum Project Finishing. Replies: 3 Last Post: , AM. Replies: 4 Last Post: , AM. Which non-poly varnish for brushing over shellac? By Andy Fox in forum Project Finishing. Replies: 4 Last Post: , PM.
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