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The unique characteristics of wood make it suitable for a variety of applications in the building industry. Log or timber homes, decks, rough sawn siding, fences and shingles. Without protection from the sun and moisture, wood ages, weathers and deteriorates.  Finishes are used to enhance appearance and dimensional stability, and to retard deterioration.

Weathering of wood is a combination of chemical,  biological and sunlight (UV) induced processes that change the appearance and structure of wood. After two months of exposure, all woods turn yellowish or brownish, and then grey. Dark woods will become lighter and light woods will eventually darker or sunburn. Surface checks, raised grain, cupping and warping develop as wood continues to weather and age. Recent research conducted by the forest product laboratory indicates that failure to properly treat new lumber can reduce the average life of wood by 20 percent.

Finishes are generally classified into two basic categories: those that form a film coating on wood and those that penetrate. Products that form a coating or film, that is a barrier between wood and the elements include latex, acrylics and varnishes. Products without pigments are considered to be clear or transparent finish, and have little or no protection from the ultraviolet (UV) radiation. Pigments are added to paints, solid color stains, and semi-transparent finishes to change or restore the appearance of the wood and to provide protection from the UV rays.

Some of the newer water-based coatings are semi-transparent acrylic blends that have excellent flexibility. Unfortunately, due to their higher molecular weight, acrylics still form a film on the surface of the wood, and are subject to the cracking that characteristic of all film forming finishes. A film finish cracks as wood expands and contracts during normal moisture cycling and water gets underneath the finish and deteriorates the wood. removing these finishes can be difficult, but is necessary before reapplication. If the failing coat is not removed, then the new coat may blister and peel.

Penetrating wood finishes are oil or water based products that saturate wood pores to prevent water penetration.They typically contain a oil and resin combination in a transparent or semi-transparent stain. Advantages of penetrating finishes over films are they provide long-term water repellency, they do not trap moisture in the wood and they do not peel or blister.

Correct application is critical to performance. All finishes should be applied to a clean surface. However, penetrating finishes should be applied to surfaces that are porous and free from previous coatings.

Although chlorine bleach will effectively remove many stains like mold and mildew, it can damage the wood and is toxic to people and plant life. Newer, chlorine free cleaners are environmentally safe and can actually increase product penetration up to 25%. Wood that is pre-treated with a cleaner or pressure washed will probably have a better finish penetration.

To avoid lap marks, particularly on hot sunny days, apply these in the shade. The cooler surface will absorb better and allow for easier application of a second coat. It will also provide a more uniform appearance.

Log structures can pose special application problems. The up facing curves of a log are subject to intense UV rays and moisture when rain and snow accumulate in cracks and crevices causing the finish to crack and peel. Log homes at higher elevations are especially subject to temperature extremes that cause wood to continually expand and contract. This effects adhesion, water repellency and color retention of finishes. Exposed end grain at corners can encourage water penetration. Make sure that end grain is adequately treated and large cracks are sealed properly. Apply finishes liberally to the course of logs near the foundation where moisture and dirt are likely to be  problem. Routine maintenance is necessary. Exposure to the elements, product choice , surface preparation, application techniques are all essential to success.

Although the wood finish is only a small percent of the cost of a log home, it is one of the more critical elements in consruction. Understanding the properties and expected performance of various products makes the decision process easier for you.