Factors Affecting Log Finishes

SEVERITY of WEATHERING

The term “weathering” is used to describe general appearances which can have a number of different causes.  The severity of weathering will probably vary with the orientation of the wall:

• Walls exposed to strong sunlight or which are constantly shaded may suffer from deterioration of the finish due to UV damage or high exposure to moisture.
• Logs on the side of the home which faces the prevailing winds may be scoured by granular particulates like sand.
• Snowdrift accumulating on the downwind side of the home can cause decay and discoloration from fungal activity when conditions are right.

DETERIORATING FACTORS

The following factors and conditions can deteriorate exterior finishes:

Mechanical

• Freeze damage- water in its liquid for becomes trapped by checking on upper surfaces of logs or design features which don’t allow for good drainage such as gaps at corner notches or window sills and door thresholds which aren’t sloped for drainage. As this water freezes it expands, widening any crack in which it happens to be trapped.
• Abrasion by windblown rain, hail, sand and dirt. Landscaping and long roof overhangs can help protect homes from these problems.
• Twisting, bowing and shrinkage as logs dry. This is usually the result of uneven or excessively rapid drying, Often (but not always) taking place before logs are installed in a home. This movement can cause cracking in the finish, allowing moisture to reach the wood surface of the logs.
• Repeated wetting and drying of the surface layers of wood produce expansion and contraction in the outer wood surfaces which don’t take place in deeper wood. These differences in movement create stresses which produce a weak layer between outer and inner wood.
• Improper methods used in the attempt to remove discoloration or old finishes, such as sandblasting or blasting with another medium such as walnut shells or corn cob can damage the surface of wood or change the ways in which it absorbs moisture or a finish coating.

Biological

• Fungal activity can cause deterioration of wood cells through consumption of wood cell contents. Acids and other metabolic products produced by fungi during decay can also deteriorate wood.
• Insect entry and exit holes can interrupt the finish integrity, allowing moisture to intrude behind the finish, promoting fungal activity.

Chemical

• Oxidation- graying of untreated wood is the result of oxidation of the outer wood cells. This is deterioration caused by oxygen in the air.
• Improper chemicals- wood finishes can be damaged by the use of improper chemicals used for cleaning, such as bleach solutions which can react with chemical compounds naturally found in wood such as iron tannates.

Sunlight

• Ultraviolet (UV) radiation in sunlight can deteriorate wood fibers at the log surface. These deteriorated fibers provide food for some types of fungi and degrade the bond between the finish coat and the log surface.

Failure to protect logs can lead to a 20% reduction in lifespan.