How to Finish Oak For Outdoor Use
Oak has long since been a favorite of many carpenters and woodworkers because of its solid but beautiful characteristics. Depending on the type of environmental exposure, the treatment and finishing process can differ. In this article, we will discuss how to finish different types of oak for outdoor use.
Depending on the desired look, the type of oak, and the wood's environment, the treatment and finishing options for oak are myriad. However, specific cardinal steps are needed for even the most basic finish. This process consists of ensuring that the wood has reached its EMC or equilibrium moisture content to prevent warping after treatment, sanding the wood with multiple different grades of sandpaper, and applying your choice of finishing chemical.
As there are many different types of oak and many applications for the use of oak, the preparations and finishing agents may differ. For this reason, there is no perfect one-shot way to finish oak for outdoor use, as different environments contain different factors that may change the way that the wood will react. However, to remedy this, we will cover some outdoor applications and how to prepare, treat and finish them.
Oak treatment and finish options
There are more than a few oak treatment finishing options that will work well for exterior uses. Below we will mention and explore each option as well as the environment in which they work best.
Before deciding on a finishing treatment, there are some factors to consider:
- Cost or pricing of the product and how much you are willing to spend on your exterior finish. Some treatment options look fantastic but are financially impractical to apply to a large surface without breaking the bank.
- The application of the finishing treatment needs to be factored into the equation. If you choose a finishing treatment product beyond your means to apply, the product's effectiveness will be compromised. Or if you decide on a product that needs to be applied regularly, you will not be able to neglect to maintain the wood, lest rot or pests sets in and cause permanent damage. Keep in mind what kind of project you will be treating and how easy or difficult it will to regularly apply the treatment in the future.
- Appearance is naturally a prominent factor to consider. This can depend on the style of your home and décor or even the design of your garden. Some of the possible options to consider are paint or semi-colored or opaque treatments like whitewash or stains that can lend a lighter, darker, or even a different hue of color to the wood. Glossy or matte clear treatments can also be mixed with stains to lend a different variation of grain contained within the wood without compromising the natural esthetic. Lastly, a simple finishing option can be utilized to maintain or bring out the natural beauty of the wood with an almost invisible appearance.
- Life cycle or maintenance is pivotal in choosing the correct treatment for outdoor oak furniture or decking. You will need to consider the use the area or furniture will experience and factor in the amount of time you have to maintain the treatment. This includes sanding or scraping the wood clean of the previous coat of treatment and reapplying it, repairing areas that became more distressed in its period of use, and the amount of time that has elapsed between the last treatment.
- Function precedes aesthetics when it comes to woodwork or carpentry, as any respectable tradesman will tell you. The same can be said for the treatment of oak wood outside. The same finish applied on a mahogany doorway will not necessarily work on an oakwood outdoor deck or chair. Keeping this in mind is essential in choosing the correct treatment option.
Preparing the oak for the finishing treatment
The preparation process is more or less the same across most species of oak wood. The process consists of sanding the wood with different grains of sandpaper. Start with a rougher grit such as 80. Then steadily progress to 120, 180, 280, and finally finishing with a fine-grit like 320. Between each sanding session, clean the surface with a cloth moistened with mineral spirits to remove sawdust and fine wooded particulates.
The sanding process is very time-consuming, and you may use a lot of sandpaper. However, it will ensure that the finish you apply to your oak wood takes to it properly and that the pores of wood absorb the finish of your choice.
As the name indicates, penetrating finishes seep into the wood and seals it from moisture, and some even protect the wood from pests. Penetrating finishes offer little to no protection against sunlight or general wear and tear but do not blister or peel, and can they usually are straightforward to apply and easy to maintain. They do, however, need to be applied regularly and offer no protection against dirt and debris.
Most penetrating finishes come in the form of teak or tung oils and semi-transparent stains that lend a natural look to the wood. They can also vary in formulations from water repellents, water-repellent preservatives, and colored water preservatives.
Water repellents and water repellent preservatives repel water but do not waterproof the wood. As mentioned above, they offer a natural look because of their clear or transparent coatings that reduce wood movement or warping. The usual ingredients for water repellents and water repellent preservatives are solvents, paraffin wax, varnish resin, or drying oil. The solvent aids the resin and wax to soak into the wood before the wax or resin evaporates.
The difference between a water repellent and a water repellent preservative is the addition of a wood preservative or mildewcide to the water repellent formulae. As the name suggests, it helps preserve and protect the wood from fungi and mildew.
Teak or Tung oil finishes bring out the natural colors of oak for a short time but have to be frequently reapplied depending on the quality of the product. If the product is not applied regularly, the wood can suffer photooxidation damage and turn a gray color.
Teak oil is not manufactured from teak trees but rather a brand name from the manufacturer that plays on the characteristic of teak wood because of its natural decay resistance and popularity. Similar products include Danish oil or Antique oil and contain a small percentage of pigments that assist them to last longer.
Tung and linseed oil are wood treatment oils that are vegetable-based. They absorb oxygen in the wood and crosslink to form polymers. For this reason, tung and linseed oil are classified as drying oils. They do not provide a lot of durability or protection from outside elements but are usually used in concert with other treatments such as varnishes to help protect the wood from fungi and sun damage.
Film Forming Finishes
These finishes are comprised of paints, polyurethanes, solid color stains, and varnishes. They generally offer excellent protection against wear and dirt, provide very long-lasting protection and come in many varieties of sheens. They are, however, more difficult and effort-consuming to apply. They can peel and blister if moisture gets under the treatment finish into the wood and are generally less forgiving when this happens.
Paint provides the longest-lasting protection amongst the film-forming finish treatments. It completely blocks ultraviolet rays and, when applied correctly, seals the wood from microbial attacks and water damage. Paint is an excellent choice for a outdoor finish if the oak wood is not exposed to regular water, as this can cause the paint to blister and peel. If this happens, the paint, like most film-forming finishes, will have to be removed with chemicals such as paint stripper and scraped from the wood before being reapplied.
The best type of paint to use on exterior finishes is the acrylic latex variety, as it lasts longer than oil-based paint and has stronger resistance to ultraviolet rays. Other advantages of acrylic latex-based paints are that they are more flexible and do not crack with age. They also allow the wood to breathe easier and shed water.
When applying paint to oak wood, it is always good to apply a primer to ensure proper adhesion. A primer will also extend the life of the paint. Remember to ensure that the wood has been prepared properly by sanding it with the various grits mentioned above.
When treating any vertical surfaces near-horizontal surfaces or any horizontal surfaces with paint, it is recommended that you apply a water repellent preservative a few days prior. This will ensure that the service life of the wood is extended and protected from splashes of water. This is useful when treating doorjambs or window jambs.
Polyurethanes and clear varnishes
These types of treatment present a nice balance between aesthetics and wood protection as they often bring out the depth and beauty of the wood while protecting it from wear, decay, and ultraviolet rays to some extend. On the other hand, they demand more effort to apply and maintain. When maintenance is neglected, these types of treatments, much like paint, have to be removed with a paint stripper and sanded off completely before reapplying.
One of the best types of clear varnishes is marine varnish, which is specially formulated to protect the wood from outdoor environmental exposure against the sun, wind, and water. Traditional marine varnishes are comprised of phenolic resins, tung oil, biocides, and ultraviolet inhibitors. New versions are formulated from Uralkyds or oil-modified urethanes and provide even greater water resistance, durability, and less expensive. However, they tend to take more effort to apply and require more maintenance in comparison to traditional varnishes.
Applying clear varnishes and polyurethanes requires equal amounts of patience and skill. The process follows more or less the same steps as the other treatments, with the oak wood being sanded with varying grits of sandpaper and cleaned with mineral spirits. After ensuring that the wood is clean and dry, you can apply the first varnish or polyurethane coat.
When applying the treatment, it is important to make sure that the coats are spread evenly, and no bubbles form. The first coat needs to be thoroughly dry before proceeding to the next step: to use a fine grit of sandpaper, around 200 or higher, to lightly sand the surface of the first coating. Afterward, it is recommended to use steel wool and damp cloth to remove any particulates before applying the second coating. After the second coating has dried, you will need to check the smoothness of the finish. If your hand glides over without sticking or hitching to the surface, the third and final coat may be applied.
If not, you will need to sand the surface again using the fine gritted sandpaper, clean it with steel wool and a damp cloth and only then apply the third coating. Please note that when wiping the varnished surfaces with a damp cloth, the surface needs to be completely dry before applying the next varnish coat. Neglecting to do so will result in the treatment bubbling or peeling.
Why do I need to finish or treat oak for outdoor use?
Most woods have to be treated before being used outdoors for any extended period of time. For most people, this is common knowledge. What's not common knowledge is why wood has to be treated as finishing products can range from seemingly unnecessary to somewhat expensive. However, regardless of the effort that goes into treating oak or how much it cost. The fact remains that it will ensure that the wood lasts longer and, in most cases, look better, which will save you the effort of replacing it and the costs attached.
The sun and how it affects oak and other wood types
One of the environmental factors that any wood needs to contend with when used outdoors is sunshine. Or, to be more specific, the UV or ultraviolet rays contained in the light directed from the sun.
While a tree is still rooted and alive, sunlight is necessary to photosynthesize and grow. However, when the tree is harvested for lumber and wood, the chlorophyll cells within the tree leaves that previously absorbed sunlight and converted it to energy, oxygen, and carbon dioxide cease to function.
This causes the wood to absorb the ultraviolet rays in a very different manner. Instead of using the ultraviolet rays in a life-sustaining manner, the wood, lacking the chlorophyll cells that leaves have, is forced to release its moisture content. This has to do with how the lignin cells inside the wood react to ultraviolet rays and the heat associated with sunlight.
The lignin cells inside wood are the cells that lend the wood its rigidity and structure. When harvested wood is exposed to direct sunlight without being treated, the moisture content contained within the lignin cells decreases. The movement of water reduces the coloration of the lignin cells, thereby bleaching them. This process is referred to as photooxidation or bleaching. When this process repeatedly occurs, the lignin cell structure can come under duress and deteriorate with time.
Although there are quite a few factors to consider when treating oak wood for outdoor use, luckily, some steps are quite standard and easy to follow, as described above. The main rule is to be cognizant of what type of finish you want and if it is practical to apply and maintain the treatment in the environment, you find yourself.
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