Shellac vs. Polyurethane vs. Varnish – The Wood Finishing FAQs
When you are into woodworking, finding the right finishing product for your furniture-making might be confusing. With so many brands and products on the market, one does not have enough time to try out each and every type of finish. Products like shellac, polyurethane and varnish are quite common. Although they have some similarities, they are not the same and you definitely cannot use them interchangeably.
In this article, we will discuss these three common types of wood finish. We will have a look at the definitions and compositions of shellac, poly, and varnish. We will also explain their origin, their respective pros & cons as well as highlight the recommended and typical uses for each one.
Shellac as Wood Finish
What Is Shellac?
Shellac is a traditional
natural finish and a sealer that dries quickly. Thus, multiple coats can be
applied in a single day. As a rule of thumb, you can usually recoat a shellac
finish after four hours from the first application.
Shellac gives a classic and warm finish without affecting the natural appearance of the wood. It has been used for thousands of years for finishing fine furniture. You can apply it easily with the help of a brush, a sprayer or a rag.
What Is Shellac Made Of?
Shellac is made of the resinous secretion of an Asian female lac bug that creates cocoons on certain trees in southern Asia. Shellac are dried in flakes and are mixed with solvents like alcohol. This process produces liquid shellac that is used as a warm-colored wood finishing product.
What Is Shellac Used For?
It makes a mellow finish
and enhances the grain pattern of the wood. While it is not toxic in its
natural form – shellac is actually used for pills and sweets as well – it is
not very resistant to heavy use, chemicals or strong heat. While it can be used
for wooden bowls or plates, it is probably not ideal for cooking spoons,
countertops or heavily used kitchen furniture.
Because of its sensitive and less durable characteristics, most people use this finish for decorative pieces only. It is usually not a recommended finish for a dining room table or kitchen furniture where you should go for a more resistant finish.
Shellac in its natural form is a finish that gives the wood surface a reddish, amber or clear color tone. However, you can also tint it if you need a different color shade for your woodworking projects.
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How to Apply Shellac?
Firstly, you will need to sand the work piece. Afterwards, you can
use a brush, a sprayer or a cloth to apply shellac. Follow the grain of the
wood. Sand the work piece again after 30-60 minutes and apply a second coat of
shellac. Depending on the expected outcome, the surface and the condition of
the wood, you may consider applying another one or more coats of shellac to
achieve the desired finish.
This product is considered as an evaporative finish: this means that the alcohol of the shellac mixture evaporates in the air while leaving behind the protective film. If you decide to use this kind of finish, you will need to maintain and refinish the treated surface frequently. Alternatively, you can use a wax-containing shellac or apply a coat of wax over dewaxed shellac – varnish and oils can also be applied over shellac. This will lead to an improved and more durable surface protection.
Dewaxed Platina Shellac Flakes
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What Are the Advantages and Disadvantages of Shellac?
Shellac makes a beautiful and somewhat protective finish for wood:
Once it is applied and dried, it enhances the natural wood grains by adding a
warm amber color shade that looks stunning on fine furniture.
However, shellac is not exactly a durable finish. It can easily be dissolved with water and alcohol. Another disadvantage is that it has a shorter “shelf life” than poly and varnish. Shellac mixed with denatured alcohol is only usable within six weeks.
More advanced and enhanced off-the-shelf shellac products come with a promise to retain their applicability for up to three years though. Make sure you read producer’s information on the can.
Polyurethane aka Poly for Finishing Wood
Find oil-based poly on Amazon.
Find water-based poly on Amazon.
What Is Poly?
Polyurethane is a synthetic resin and a wood finish used for floors, cabinets, doors, windows and other wooden installations. Unlike shellac, it is quite durable and long-lasting. It will also protect these wooden pieces from water, fungus, mildew and abrasion.
Poly is available in two types: water-based and oil-based which is also known as solvent-based (read more about water- vs. oil-based poly in our dedicated article).
What Is Polyurethane Made Of?
Oil-based Poly is made of a natural oil (e.g. linseed) in a chemical reaction with polyhydric alcohol and disocyanate. The type of oil used for the production determines the color shade of the poly. Find more details on Polyurethanes.org.
Water-based polyurethane, on the other hand, consists of water and urethane resin. Its technically correct name would probably be “water-borne acrylics mixed with urethane resin”.
What Is Polyurethane Used For?
Water-based polys are perfect for bookcases, desks, side tables, finishing and refinishing
floors, and beds. They produce a flat to glossy luster.
Oil-based poly is often thought of as being more durable. However, these polyurethanes are used in similar areas as the water-based ones but may be preferred for items subject to heavy use.
How to Apply Poly?
Poly can be applied easily with a brush but you can also use spray equipment. The application of water-based and oil-based products is similar – both require a sanded surface, for instance.
Water-based polys are usually applied with a synthetic-bristle brush or a foam roller – even a rag can be good enough though.
The application of oil-based polyurethanes is very similar: you can use a foam or nylon brush. For a smooth look, you need to work yourself through three to four coats and sand the surface lightly in between the coats.
Oil-based polys are toxic while water-based are less or non-toxic at all (check the back of the can for details). When applying the Polyurethane, you want to make sure that there is enough ventilation and air circulation in your work areas. You should also put on protective gloves and clothes along with a respiratory mask. Read more about DIY safety in our dedicated article.
While both water- and oil-based polys penetrate the wood, the oil-based ones do so more intensely and add color to the wood texture.
It is often thought that polyurethane let wood appear in a plastic-like look. However, this is usually an outcome of the way of application rather than a characteristic of poly itself: If you apply it in a thick layer it will indeed appear cloudy and unnatural even though it is not a plastic film.
A respirator is highly recommended when working with poly.
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How Long Does It Take for Polyurethane to Dry?
goes through several phases of drying or, more precisely, curing:
If you are using an oil-based Polyurethane, you can usually touch the surface without leaving prints or apply another coat after 24 hours. You can carefully start walking on a floor (with socks) 1-2 days after applying the final coat. Allow a table finished with Poly a bit more time to dry though – consider a careful use after 2 to 5 days.
However, wait until the stickiness of the surface is gone before you use it in a normal way and put things on it for a longer time. This should be the case after 1 to 3 weeks.
Water-based Poly requires significantly less drying time: Additional coats can be applied after 3 to 4 hours and you can walk on a floor wearing socks after 4 – 8 hours.
These numbers depend on a number of factors, of course. These include but are not limited to the type of poly that you are using, the humidity, the temperature, the quality of the sanding etc.
What Are the Advantages and Disadvantages of Poly?
polyurethanes are much safer and low in toxicity. They have been becoming
popular these days, mainly because of their clear finish and low odor.
Water-based polys dry much faster than oil-based polys. Compared to shellac,
Polyurethane is more resistant to rough conditions and humidity. However, it is
also not ideal for areas exposed to extreme heat or chemicals.
Oil-based or solved-based polyurethane is much more durable than water-based polys and shellac. It is a good choice for areas exposed to heat and chemicals like kitchen furniture. Chemicals can be e.g. acids as in vinegar and other food items.
Polyurethane must be applied very neatly and accurately. You should avoid having uneven or too thick layers. Applying too many layers without a sufficient curing in between will let the wood surface look plastic-like. So, be careful when working with Poly, particularly oil-based poly, to make sure the wood keeps a natural appearance
Many types of polys turn yellow over time because of the UV radiations.
Varnish as Wood Finish
Varnish used for banisters.
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What Is Varnish?
is actually a broadly used term referring to a clear, transparent and hard
protective film used for wood finishing. Varnishes are available in a lot of
combinations and products on the market. All of them will give your furniture
or wooden installations gloss and protection.
Varnish has been in use for thousands of years. Many believe that it was originally developed by the ancient Egyptians.
What Is Varnish Made Of?
Varnish is made of oils like Tung or linseed oil, a solvent or thinner and a natural or synthetic resin.
What Is Varnish Used For?
probably provides the most durable finish compared to other products. This is
because it contains a higher ratio of solids that harden the film. Unlike
Shellac, varnish creates a surface that is impervious to chemicals and
solvents. Even if you poured alcohol on the finished surface, the varnish would
not get dissolved – an advantage compared to shellac.
Therefore, varnish – in particular spar varnish – is an ideal choice for outdoor installations, e.g. exterior doors. It protects the wood from ultraviolet radiations and water.
This is the reason why they are ideal for wood items that will remain in or near the water, like boats, decks or beach chairs, for instance.
How to Varnish Wood?
As a first step, you will have to sand the work piece and remove any previous finish. The varnish comes either as a spray or can be applied with a brush or a foam applicator. You can thin the varnish, if necessary. You should follow the grain and allow the coat to dry for at least 24 hours.
Apply another coat after sanding, let it dry and repeat these steps until you get the desired result. The drying time of varnishes varies significantly. It can be as short as 1 day up to a couple of weeks, depending on the composition of the product. Check the producer’s recommendation and the timeline for your project before buying the varnish.
Varnish finishes are usually a bit “heavier” and thicker, so you might only need 1 to 3 coats to get a perfect finish. Varnish finishes are a bit rougher than the shellac finish. If they are applied correctly, they are not brittle though. You can find more details on Wikihow.
Varnish, Shellac or Poly – Which One You Should Use For Your Project
Now that you’ve got the basic introduction, pros, and cons of various types of wood finish it will be a lot easier for you to find the perfect finish for your maintenance work or woodworking projects.
For exterior woods exposed to UV radiations, all weathers conditions and water or rain, varnish is a good choice as it is durable, UV resistant and therefore will protect your wooden doors and other wood items. However, the application of varnish requires more time an effort – it is not as straightforward and simple as for shellac and poly, and it might take a long time for it to dry. Compare the different types of varnish on Amazon.
For finishing kitchen cabinets, floors, windows, doors, dining tables and other areas that are exposed to heavy use, you will want to consider going for a polyurethane finish. Read our dedicated article on poly with a detailed comparison of oil- and water-based polys or take a look at the available Polyurethanes on Amazon.
Shellac, on the other hand, is a quick and natural finish. It is ideal for items that are not exposed to intense use, like decorative objects or antiques. For these pieces, shellac also enhances the natural grain texture of the wood. Check current Shellac prices on Amazon.
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