Wood is an immensely-used and widely popular material for various applications. We find wooden items all over our homes. In cold regions, you will find wood that makes up the flooring. You can also see complete buildings made of wood. Then, wood plays a prominent role in furniture and outdoor accessories like decks, railings, and patios.
Wood is very rarely left its own after being processed. Wooden surfaces need to get some smoothening treatment like sanding, and then a finish has to be applied to it. A finish can take the form of paint, varnish, oil, or stain. Varnish and stains are two widely-used substances for applying a finish to the surface of the wood. We use a finish to enhance the look of the wood and to make it more durable.
There is often confusion between varnish and stain, so we attempt to put all doubts to rest in this post. Here, we discuss each wood finish in detail, pointing out the differences and similarities. We also go into detail regarding how you can best use each of these two wood finishes. Once you have read this post, you should be able to distinguish between a stain and varnish and will be able to decide the right type of finish for your woodworking projects. So, let’s jump right in!
Varnish vs. Stain
To know how and where to use varnish and stain, we need to gain a full understanding of the difference between these two surface treatments. The primary difference between the two is that a stain penetrates the wood and serves to change the natural color of the wood. Varnish, on the other hand, remains on the surface of the wood and forms a protective barrier.
What is Varnish?
We use varnish to protect the surface of wood, but also to enhance its good looks. Varnish usually is transparent and hardens to form a protective film once dry. Some varnishes contain color for added effect. You can get varnishes in different finishes like satin and gloss. Before you use varnish, you should check if it is suitable for use outdoors or indoors.
How to Apply Varnish
To apply varnish well, you first need to prepare the surface of the wood. The varnish will highlight any blemishes on the surface, so you don’t want that to happen. Use sandpaper of medium or coarse grit to smoothen the surface. Once done and you have filled cracks and crevices, if any, you can start applying the varnish.
The first varnish coat will act as a primer, and you should use a thin coat containing 10% of white spirit. It mainly applies to polyurethane varnish. The best way of applying varnish to the wood is by using a lint-free cloth. However, it is not uncommon to see woodworkers applying it with a brush or a roller.
Once you apply the first coat, you need to rub it down with fine-grit sandpaper or 0000 steel wool. We call this process, “keying.” While applying successive coats of varnish, you need to ensure that the surface is free of blemishes, debris, and dust.
Types of Varnish
Given below are the main varieties of varnish that we use to finish wood in woodworking:
We use this varnish for finishing wooden items that we leave outdoors. It protects the wood from the ultraviolet (UV) rays of the sun. Another property of this varnish is that it is microporous, meaning that the wood can “breathe” through its layers. It contains a fungicide that prevents the accumulation of mold and mildew. This variety of varnish shares similarities with yacht varnish, which we mention further down in this list. It has a fair degree of flexibility but takes time to cure
This water-based varnish is non-toxic and quick drying. It has resistance to UV rays, which makes it suitable for use outdoors. You can use acrylic varnish on non-wood surfaces as well, with satisfactory results. It is transparent and is not likely to become yellow, like many other types of varnish. One drawback of acrylic varnish is that it doesn’t penetrate wood very well. It is easy to maintain. Since it is a water-based varnish, you can clean surfaces finished with acrylic varnish by using water. It comes in gloss, matte and satin finishes.
Polyurethane varnish creates a tough surface once cured. We use it on wood that will receive much wear and tear like flooring. It has a high degree of heat resistance, as well. With polyurethane varnish, you get a clear and hard finish that comes in gloss, satin, or matte. Because this varnish has less tendency to penetrate wood, we often use an oil-based varnish primer for the first coat. However, an oil-based varnish will not bond on TOP of polyurethane varnish.
The advantages of polyurethane varnish are that it is tough and durable on curing. It shows resistance to mild acids, solvents, and various chemicals, and has less tendency to become yellow over time. Regular polyurethane varnish does not offer UV protection. If you need to use it for outdoor applications, you need to procure varnish with added UV protection.
We often add this type of varnish to other varieties of varnish. Alkyd varnish is modified vegetable oil. It is a clear wood varnish extracted from alkyd resin. It offers adequate UV protection so that you can use it indoors as well as outdoors. You can use alkyd varnish on MDF and many varieties of wood. It is possible to use it to cover existing paint, but you need to take care that the surface is clean and free from flaking.
The other names for this varnish are “spar” and “marine” varnish. Originally it coated the wood on boats due to the flexible but watertight film that it forms. Way back then, gloss and UV protection was low on priority. Today, you can get yacht varnish with added tung oil and phenolic substances to impart a high gloss to the surface.
We can consider shellac more as resin than a varnish. It comes from the “stick lac” secretion of the female lac bug, an insect that lives in the forests of southeast Asia. After being refined, we process shellac into flake form. It is the commonest form in which we get shellac. We dissolve these flakes in alcohol to use it. It comes as clear varnish, but you can get it in different shades from light yellow to brown. Shellac is the main ingredient for applying French polish, which is not polish but a technique of applying polish highlighted in detail in another post.
Like shellac, we also do not consider lacquer to be a varnish. In the same way that French polish is actually a technique of finishing a wood surface, lacquer is also a process. We have added it to our list because it is a name that pops up frequently in any discussion concerning varnish and stains. It refers to applying a finish by spraying. The solvent base we use usually is acetone, also known as “lacquer thinner.” Here, there is no polymerization process involved the way genuine varnish polymerizes.
Here is another category on our list that does not include varnishes in the real sense. The term “drying oils” is a bit of a misnomer because some of the raw drying oils can take several weeks to dry. Then, there are raw oils like raw linseed oil that sometimes never dry completely. You will find a variety of these oils in the market. We often mix them into varnish and also use additives to help these oils to polymerize. Two of the most commonly used drying oils are tung oil and boiled linseed oil which you can read in another interesting post of ours.
What is a Stain?
A stain is a substance we use to change the wood’s color to bring out its natural shade. Although wood receives a certain level of protection from a stain, the primary purpose of a stain is to improve the wood’s appearance. A common practice is to use a top coating over a stain.
Parts of a Stain
Wood stains share a similarity to paint, although it will form a protective film on the wood’s surface. A stain gets absorbed into the wood so that we can see the grain of the wood through the stain. The extent of the wood grain that you can see will depend on the opacity of the stain.
Pigment is the color component of a stain. Some differentiate between the different types of pigment, but it doesn’t change anything for the user. You can get various tints for stains, but the commonest ones are different shades of brown.
Solvent or Vehicle
It is the substance that transports the pigment into the substrate (wood surface). It makes the stain easy to apply. The solvent is a volatile liquid like some form of spirit or alcohol. After application, the solvent dries, leaving behind the pigment.
The binder is the ingredient that holds the pigment onto the wood. We can consider this as a type of liquid adhesive. It dries to form a hard film of pigment on the surface of the wood.
How to Apply a Stain
You should prepare the surface for applying a stain in the same way as preparation prior to varnishing. Cover all the cracks with medium-grit sandpaper. Add a filler that will not show up after staining the surface. A lint-free cloth works best for applying stain to the wood. Ensure to blend the wet and dry edges together to disguise lines and overlaps.
Be cautious while using water-based stains because there is a likelihood of the fibers getting raised, causing blemishes in your finish. Move the stain along the grain rather than across it and avoid overloading the cloth to prevent it from dripping. You can rub sandpaper over the surface between coats, once the stain is dry. The more coats you apply, the darker your wood surface will become.
Applying a stain is an acquired skill. Hence, it is good to apply a trial stain on a scrap piece of wood first, especially if you are a novice. It is common for even experienced woodworkers to do this. If you don’t apply it properly or your shade is not quite right, it will be very difficult to correct it, especially after the stain dries. Hence, a trial application on a piece of scrap wood is a good idea.
After reading this post, you should be clear about the differences between varnish and stain and, more importantly, how and where to apply them. You will have also seen how the two can complement each other. Once you know all this and are aware of the different types of varnish you can use, you will be able to come up with some excellent finishes in your woodworking projects.