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All About Wood Finishes

Beginning woodworkers usually have a hard time applying a finish to a project. It seems like nobody cares how hard some joinery or teeny-tiny machining, but when it comes to putting a finish on their work, most woodworkers get as shy as a teenage boy on a first date. “Is this the best finish for my project?” is one I hear a lot.
An Initiation Rite
Once you can answer that question calmly, confidently, and comfortably, you’ve passed a major initiation in the world of wood. Knowing your finishing products really isn’t that hard. They only come in a few, easy to learn categories based on what they do to the wood and how much protection they offer. Wasex, oils, varnishes, shellacs, lacquers and water-based finishes. You use a different finish depending o how much protection, durability, repairablilty, look, and how easy to use it is.
Sadly, there aren’t any finishes that do all of the above. A finish that works great in one aspect may fail miserably in another. When choosing a finish, there’s going to be some trade-off.
Remember, you want to choose a finish based on how well you need to protect the surface, how long it will hold, and how easy to use it is, as well as how you want it to look.
Types of Finishes
Let’s go over the categories for wood finishes again. There are really only two distinctly different types of wood finishes, based on how they dry or cure. Evaporative finishes, like lacquer, shellac, and most water-based finishes, dry to a hard film as the solvents evaporate out. See how they named that?
Water isn’t a solvent itself, it’s just the carrier for the finish emulsion. These types of finishes will always dissolve again if you use the solvent used to then them, even after they’ve dried. They don’t tend to be as durable as the next type, reactive finishes Reactive Finishes, like linseed or tung oil, catalyzed lacquers, and varnishes, also have solvents that evaporate, but they cure by reacting with air when taken out of the can or a chemical placed in the can before applied to the wood. They actually change at a chemical level as they dry, and after they finish will NOT redissolve in the solvent originally used to thin them. Unless you’re talking about pure oils, reactive finishes tend to last longer, endure more, and generally hold up better against heat, water, and chemicals. Some people use waxes as a finish, but I don’t think by itself it does the job.
You can use paste wax (carnauba or beeswax work well) to polish your furniture but only over another finish, like a lacquer or shellac. True oils like linseed oil and tung oil, (drying oils most often used in finishing) are available at almost any hardware store at very low prices. They’re called true oils to distinguish them from other products advertised as oil finishes and to separate them from naturally nondrying or semi-drying oils used in finishes like soybean oil.
True Oils
True oils change from a liquid to a solid. This makes your project stronger after the finish has cured. Linseed oil comes in many forms. You can get it unrefined, where it’s called raw linseed oil, but it’s not generally a good idea because it takes so long to dry. Ancient finishers figured out that by boiling the oil, they could make a thicker, faster drying product that worked just as well. These are called heat treated or polymerized oil. Most of the time you’ll find boiled linseed oil with raw oil that’s been mixed with additive chemicals to speed drying time. Makes a woodworkers life easier!
For finishing wood projects, you should ONLY use boiled linseed oil. Tung oil actually comes from tree nuts native to Asia. Luckily for us, other parts of the world have begun growing them too. You can get Tung oil in it’s pure form or, like linseed oil, get the heat-treated or polymerized form. The heat-treating process makes the oil durable, and it speeds up drying time. It also lessens Tung oil’s annoying habit of “frosting” your project, or drying to that white, matte look.
Tung oil is a paler color, and it holds up better against moisture than linseed oil does. Linseed and Tung oil are both penetrating finishes. that means they actually penetrate the fibers of the wood before they harden, making them stronger. They’re also the easiest finishes to apply. You wipe them on, you let them penetrate the wood surface, then you wipe off the excess with a rag.
Unlike varnish and lacquer, these oils aren’t built up with enough coats to form a film on the surface, because the film is too soft.
Varnish
Varnishes are made of tough, durable resins (synthetics), that are modified with drying oils. If you look on cans of varnish, you will see a list of resins like alkyd, phenolic, and urethane, along with tung and linseed oils and other semidrying oils, like soybean and safflower. Varnish acts like true oils when it cures, but the resins make the wood even MORE durable than the oils do. Oil based varnish is the the most durable finish that can be easily applied by most woodworkers.
Varnish resistance is great against chemicals, solvents, heat, and water. If they have a high percentage of oil, we call them long-oil varnishes. Those are usually used for marine, spar, or exterior varnishes, though you will occasionally see some interior varnishes for sale on the market. Long-oil varnishes are more elastic and soft than medium and short-oil varnishes. Most interior varnishes you’ll find on the market are Medium-oil.
Short-oil varnishes (or heat-set varnishes, also called baking enamels) need EXTREME temperatures to dry. That makes them impractical for most woodworkers other than industrial companies. The resin used in the varnish will determine how the finish looks. Alkyd varnish is the standard all-purpose interior varnish. It has decent protective qualities, though certainly not the leader. Phenolic varnish is usually made with tung oil, and is mostly meant for outdoor use.
Urethane varnish, or polyurethane, means better heat resistance, more solvent resistance, and more abrasion resistance than any other varnish. Usually, varnish is applied with a brush. You can also get a thinned, gelled version called wiping varnish you can apply with a rag. Oil and Varnish Blends are mixtures made with oils and varnish added. They offer a nice mix of both ingredients. They apply easily, like true oils, and they protect well, like a varnish.
Most manufacturers won’t disclose their varnish-oil ratio for copyright reasons, so that makes it hard to pick a specific brand of products to recommend.
Blends dry harder than true oils and build quicker with fewer applications.
Shellacs
Shellacs are usually thought of as a liquid finish at a paint store. The weird thing? It’s actually a resin secreted from a BUG that feeds on trees. The bugs secrete it in the form of cocoons, which are then gathered and refined into dry flakes. Then they dissolve them into denatured alcohol to make the shellac solution. You can get shellac in several varieties. It comes premixed, or you can buy it in flake form and mix it with your own denatured alcohol. Premixed comes in an amber color or clear.
You can get shellac in several varieties. It comes premixed, or you can buy it in flake form and mix it with your own denatured alcohol. Premixed comes in an amber color or clear. If you get the flakes, you can get them in a wider variety of colors and wax content than premixed. The wax decreases the finish’s water-resistance, and it prevents some finishes from bonding to it.
Lacquers
Lacquers are regarded by most professionals as the go-to finish for wood. It dries fast, it gives the wood depth and richness, gives decent durability, and it rubs out well. You can get all kinds of different lacquer, and they each do different things. Nitrocellulose lacquer is the most readily available. If the label says lacquer, it’s probably nitrocellulose. It’s made from alkyd and nitrocellulose resin, which is then mixed and dissolved with solvents that evaporate quickly. It gives moderate water resistance, but doesn’t do so well with heat and some solvents. The biggest drawback is the lacquer’s tendency to yellow as it ages, which shows clearly on light-colored woods.
Acrylic-modified lacquer is made from a mixture of a nonyellowing cellulose resin (called cellulose acetate butyrate, or CAB) and acrylic. This lacquer possesses the same general properties of nitrocellulose lacquer, except it is absolutely water-white, meaning it will not show as an amber color when applied over light-colored woods. It possesses the same general properties of the nitrocellulose lacquer, but it’s water-white, which means it won’t show an amber color when you apply it over light woods. It also means it won’t yellow as it ages.
Catalyzed lacquer is bridge between the application side of nitrocellulose lacquer and the varnish durability (it’s strong and it’s easy to apply). Catalyzed lacquer is a finish made of urea formaldehyde or urea melamine and an alkyd with added nitrocellulose resin. That makes it handle like regular lacquer. If you use an acid catalyst, it starts a chemical reaction that forms a tough, super-durable finish. You can get catalyzed lacquer in two versions – Pre-catalyzed or post-catalyzed. If you get pre-catalyzed, everything is already premixed; Post-catalyzed lacquer is a two-part system that you mix yourself, but you must follow precise ratios. Once you add the catalyst, these tend to have a short pot life so use them fast!
Water Based Finishes
Water Based finishes contain several of the same ingredients as varnish and lacquer, but many of the flammable and polluting ingredients have been replaced with water, making it perfect for a more green-oriented workshop. It makes for some complicated chemistry.
Resins generally don’t like water, so they have to be modified chemically so they combine with water. Water-based finishes are usually med with an acrylic resin (called water-based lacquer) or acrylic urethan mix (called water-based polyurethane). Like varnish, the urethane makes the resin tougher and more resistant to scrathes. Sadly, water-based urethane doesn’t have the same solvent or heat resistance as the oil-based kinds.

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Thank you for reading the article above. Many important points you need to know.
Have you ever:
– Wanted to build something, because you cannot find it “retail”?
– Thought of making something custom for a specific need?
– Struggled to find detailed plans to build your dream project?

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