What to look for in an Exterior Finish

When selecting an exterior wood finish you hope that you are going to buy a product that will protect wood from the elements. You also trust that the person selling it to you has some deeper knowledge about what a good exterior wood finish is. However, in most instances the product that you buy has its shortcomings and the person selling it to you has probably never restored and finished wood professionally.

So how can you select the best finish for your situation?

Consider These Qualities When Selecting A Wood Finish


Wood is protected from the inside out. The high quality linseed, tung, and other natural oils in Wood Iron penetrate into the wood surface. Once inside, the oils bond with the wood fibers and solidify (see solids). The solids bonded with the wood fiber help the wood retain its strength and structural integrity. No other exterior wood finish has the solids content that Wood Iron has.


Wood is subject to damage from the sun. Ultra-violet rays bombard the surface of exposed wood. Without protection from this element wood will bleach out and eventually deteriorate. Most exterior wood finishes use semi-opaque pigments to obscure the wood from the sun to give it protection. Unfortunately, the beauty of the wood is obscured too. Ultra-violet absorbers in the Clear help protect wood from sun damage. Add double protection by using Wood Iron’s transparent-oxide pigments. Transparent oxide pigments will accentuate, not hide, the beauty of the wood grain.


Water damages wood when the water is absorbed into the wood. Not only does water tend to wash out the wood’s color but the freeze/thaw cycle can damage wood’s structure. Other water repellents are paraffin-based and soften with warm weather. Wood Iron has a water repellent that fills the wood cells and holds out the water. This repellent is firm in all temperatures.

Fungus and Mildew

Wood is a natural food source for certain types of fungus and spora. If allowed to grow these tiny plants devour the binding resin in wood causing it to fall apart. Some manufacturers use highly toxic poisons to kill any mildew that comes into contact with it. Wood Iron uses an organically based mildew inhibitor that is very low in toxicity and lasts up to five times longer than inorganic mildewcides.

The Look of Wood

Wood Iron is specifically designed to protect wood from all of the elements. It is sold by experienced applicators and coatings professionals, not just sales people. The intent of the manufacturer and distributor alike is to provide the best possible exterior wood finish available. Representation is the key to our reputation.

According to the October 2000 issue of Consumer Report (CR) on semi-transparent stains, one should be extremely cautious when it comes to selecting an exterior finish. CR states, “the exterior semi-transparent stains tested performed so poorly that CR won’t report on them any longer.” CR exclusively recommends a solid body, opaque stain – period.

A solid body opaque stain? What if you want the character and beauty of the wood to be visible?

Should your wood look like this?
It won’t if you use a solid body stain as recommended by Consumer Reports.

Characteristics Of An Exterior Wood Finish

How to Judge the Value of an Exterior Wood Finish:

  1. Enhances the beauty and character of the wood rather than covering it up
  2. Is easy to re-coat with minimal problems and expense
  3. Is durable enough to last a realistic yet reasonable length of time (3 to 5 years vertical surface, 1 to 2 years for horizontal surfaces)

The Key to the successful selection of an exterior finish is understanding:
ALL Products Fail.

It is HOW they fail over time that makes the difference between a Good Finish and a Bad Finish.

How to Gauge / Compare Exterior Finishes

Ask yourself, “How will this product eventually fail?” If the answer does not meet the three characteristics previously listed, move on. Find the product that provides you the desired results that you need.No wood finish will last forever. But, if a selection is based on hype and misinformation, restoration will be required very soon. Restoration is expensive and can be avoided if the choice is based on the characteristics listed for selecting an exterior finish.

There are a variety of finishes available on the market. That variety can make the selection process even more difficult. As a side note you should be aware that 95% of the products available have mineral spirits or some other type of solvent in them. Acrylic and water-borne finishes also contains solvents. A reasonable amount of solvent is necessary to obtain the finish characteristics desired. When selecting an exterior wood finish, ask yourself: How will this finish look over the years, especially after three or four coats of application? Then ask: How will this product fail? Have an idea of the right answers before asking product representatives. Then see if they give you a straight answer.


  • Acrylic-based Finishes: Similar to paint in that it sits on surface of the wood. How does it eventually fail? Peeling is a major indicator of failure. What has to be done when it peels? All of it has to come off and then be reapplied.
  • Varnishes: What is the indicator of failure? Peeling, the same as acrylic-based.
  • Oil Emulsions: These finishes are made of oils such as linseed or tung oil dispersed in water, mineral spirit and co-solvents. The water evaporates and the oils soak into the wood. These products eventually fail by oxidizing or becoming chalky. When the finish oxidizes, the surface should first be washed to remove the chalkiness then re-application of the product can be done relatively easily.
  • Penetrating Oil-Based Finishes: This particular finish is the most common product on the market. It is composed of a combination of drying oils, such as linseed oil, and solvent. Some products contain a blend of oils and resins to enhance durability. These finishes penetrate the deepest into the wood to give the wood a finish from the inside out. Eventually, the finish also fails from oxidization and becomes chalky. By rinsing and re-coating, the wood can be maintained and renewed, like oiling wood furniture. One of the differences between oil emulsions and penetrating oil finishes is that the penetrating finish absorbs into the wood much deeper, especially if the finish is brushed in.

Remember to choose an exterior finish that:

  1. Does not cover up the wood
  2. Weathers in a way that is easy to maintain
  3. Lasts three to five years between recoats

Follow those guidelines and you will have chosen a good exterior wood finish regardless of what CR said.

Note: Any finish can be applied incorrectly and become a “Bad” finish. Always follow the directions on the label when using any finish.