Types of Clear Wood Finishes
Choose Right Wood Finish for Your Project

Clear wood finishes are both beautiful and tuff, providing a high degree of chemical and abrasion resistance. All act as a wood sealer, protecting the wood fibers from water and cleaning chemicals. They can be applied to a wide range of materials, including stained windows, doors, trim and furniture.

The job of clear wood finishes is to protect your wood from water, dirt and grime plus the wear and tear of everyday life. There is a wide array of clear protective wood sealers on the market, each providing a different level of protection.

The large variety of products and brands can make choosing the right clear wood finishes seem difficult and frustrating. As you walk through the painting section of any home improvement center, you will be inundated by dozens of products, all of them claiming to be the best.

Fortunately choosing a clear protective topcoat isn't as confusing as it seems. Every type can be grouped together based on some simple characteristics.

There is two different ways to look at it. One way is how the finish is applied. These categories are wipe-on, brush-on and spray-only.

Another way is what is left behind after the finish is applied. In this case there are two different categories; film forming finishes and penetrating finishes.

Fortunately, the variety of clear protective wood finishes you will encounter and consider using around your home is rather limited. Many finishes are available in a wide range if sheens and suitable for many different environments. Each type has its own merits.

Choosing the best clear wood sealer for your project involves understanding the environmental conditions the wood will be subjected to and the amount of abrasion resistance you need. Although the intended uses for each is somewhat different, all of these wood finishes will provide a high degree of beauty to any wood surface.

Penetrating Wood Finishes

Penetrating finishes are absorbed into the wood pours with very little remaining on top. All of the penetrating finishes are wipe-on types, even if they are initially applied with a brush. The excess is removed after a short period, usually 5-10 minutes.

Examples;

• Linseed Oil – Mostly used on exterior wood siding and log homes.
• Tung Oil – Interior use is most common, can be used on food contact surfaces.
• Danish Oil- Can be used on interior doors and trim.

Tung Oil and Linseed Oil are called drying oils. This type of wood sealer can take a long time to dry to the touch. Linseed oil can take days in most cases and remain rather soft for a very long time. Typical use is outside; example would be a log home.

Applying Linseed Oil is easy although messy. Tung Oil has been used for centuries and is an excellent wood sealer for interior and many exterior wood surfaces. Applying Tung Oil is very simple with maintenance being as easy as applying another coat.

Danish Oil is a combination of Tung Oil and varnish with pigments add for color. Danish Oil is applied in the same way as the other penetrating finishes.

Film Forming Wood Finishes

Film forming wood topcoats have limited penetrating capabilities and remain on top of the wood. They can be the toughest clear topcoats but not necessarily the best for every project.

Examples;

• Varnish (Brush-On and Spray) - Varnish is similar to the drying oils but have specialized resins that provide faster drying and a much harder finish. These are available in a wide array of sheens and degrees of hardness. Plus, some varieties are great for exterior use. Most applications are a multi-step process. Applying varnish produces a tough film on the surface of the wood.
• Polyurethane (Brush-On and Spray) - Polyurethane is very popular now days, available everywhere and not to expensive. This clear topcoat is best suited for new wood applications. Basically polyurethane is a plastic coating, with interior and exterior uses. Some poly's can also be tinted for special effects. Applying polyurethane is the same as varnish, needing a few steps to do it right.
• Acrylic Urethane (Brush-On and Spray) - Acrylic Urethane is rather new to the market. Best suited for interior use, but exterior varieties are now being produced. I like this type of finish. It doesn’t smell bad and dries fast. The best part is it cleans up with soap and water. Usually takes a few coats to achieve a good film thickness. Applying acrylic urethane is easy, can be brushed or sprayed.
• Lacquer (Spray Only and Brush-On) - Lacquer is a common interior wood finish that is available with varying degrees of hardness. Typically this is a spray only finish. Spraying lacquer will require some finesse. Brushing lacquers are rarely used today with so many other alternatives.
• Catalyzed Clear Topcoats (Spray Only) - Catalyzed topcoats are a little different than anything else you will ever encounter. These are 2 part wood finishes that are difficult to use. Usually very hard and durable, this is a common finish used on cabinets. Rarely used by the do-it-yourselfer, but still a good choice for wood surfaces that needs extra protection and abrasion resistance.
• Shellac (Brush-On) - Shellac is a natural resin dissolved in denatured alcohol and is applied with a brush. Shellac has good durability but is a little difficult to apply, it dries within seconds. Even though this is a natural resin it isn’t recommended for food contact surfaces.

Compatibility between Different Wood Finishes

In order to refinish any woodwork you will need to know what type of finish is on the woodwork and decide on a new product for the topcoat. Unfortunately, not all clear wood finishes are compatible with each other.

Every manufacture has there own formulations. Using just a single different ingredient can cause a weak bond between two different products. This can be a serous problem that won’t be realized until it’s too late.

Good rules to follow are;

• Try to remove all of the old fish whenever possible. This will eliminate any incompatablility between the old and new finishes.
• Don’t change to a different manufacture or type of finish in the middle of a project.
• Lacquer, and other "hot" finishes, will damage the other film forming finishes causing cracking and possible flaking.
• Tung and linseed oil can be applied over themselves but not over anything else.
• A good wood varnish can be applied over polyurethane, lacquer, water base finishes and any other film forming wood finish.
• Polyurethane must be applied over itself only.
• When in doubt use a high quality wood varnish.