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What is Causing Wood Damage? Coastal Living and Effects of UV Light

Protecting wood surfaces in a beach or water front environment is a challenging task.  You are faced with numerous variables that contribute to erosion and degradation of the substrate including sunlight, wind, moisture, salt, and sand.  The two most destructive environmental variables to an exterior coating system and wood are sunlight and water.

sunlight damage

uniform sunexposureSunlight is the major cause of damage to a number of materials, including plastics, textile, wood, coatings, and other organic materials.  The type of damage, such as loss of gloss, chalking, elasticity, adhesion, and color change, varies depending on the material sensitivity and the spectrum of sunlight.  Spectral sensitivity varies from material to material.

One component of sunlight is ultraviolet light, commonly referred to as UV.  UV light is responsible for most damage to exposed wood because it changes or destroys the wood’s lignin, a component of wood that hardens and strengthens the cell walls.  In more scientific terms this process is called photo-oxidation.  The colorants contained in the color coats are responsible for absorbing UV light.  The more colorant a finish contains the less UV light will get through to the wood itself. 

Opaque finishes like paint and solid body stains are very efficient in blocking all of UV light from hitting the wood.  That’s why when they peel off the freshly exposed wood may still look bright.  On the other hand the objective of transparent stains is to allow the character of the wood to show through the finish. 

In order to accomplish this transparency the pigment loading is significantly less than that contained in opaque finishes.  Although some of the UV is blocked by the colorants, enough of it gets through to eventually photo-oxidize the wood.  Since darker colors typically contain more colorant than lighter ones they tend to last longer.  However, some lighter colors that contain titanium white, or KX colorant, also contain a high colorant loading which extends their life but they do give up some degree of transparency in return. 

Lighter colored stains that contain titanium white (KX) will also absorb less heat; therefore, there will be less overall stress (day surface temperature versus night surface temperature) that the finish system and wood substrate is exposed to over the course of a 24 hour period.

Squared logs, timbers, and vertical flat siding are easier to maintain since the sun hits these wood pieces at the same angle and the UV light is evenly distributed over the entire surface.   In addition, the flat vertical surfaces cannot accumulate snow and ice and even upward facing checks are not as prone to rainwater entering the logs.  Squared wood pieces are subject to the same weathering parameters as round surfaces, but the weathering is mostly uniform over the entire exposed surface.

The second challenging variable for wood in a coastal environment is moisture.  Coastal areas are notorious for their high relative humidity and pop-up thunderstorms. Keeping wood dry is the goal to protecting its long term integrity.  If wood remains wet for long periods of time without drying out, conditions are favorable for the formation of wood decay fungi, the precursor to wood rot. Four conditions are necessary for the development of wood decay producing fungi. Eliminate any one of these and decay fungi cannot survive: Oxygen, Temperature (40° - 90°F), Moisture content in excess of the fiber saturation point (> 25-30%), and a suitable source of energy and nutrients (i.e. the wood).

Recommendations:

  1. There are two basic ways to combat the effects of weathering.  By far the most effective method is to keep wood surfaces in the shade as much as possible by extending roof overhangs or constructing roofed porches around the home.
  2. Keep all vegetation at least 24 inches away from wood surfaces to allow for adequate ventilation and drying out of these surfaces.
  3. Clean the wood surfaces to remove all foreign materials from the wood prior to the application of an exterior finish system. The overall performance of even the best finish system is dependent upon proper surface preparation and application technique.
  4. Select and apply a highly durable exterior semi-transparent stain, like LIFELINE™ ULTRA-2 or ULTRA-7 to protect the wood and enjoy the beauty of the wood grain.  Select LIFELINE™ ACCENTS to highlight wood timbers and trim if more opacity is desired.
  5. Select a color that contains shades of brown, red, or gray. Consider colors that contain titanium white (KX) for lower surface temperature swings as well as good UV protection. (colors: Butternut, Wheat, Driftwood, Stone Gray or Gentry Gray).lifeline stains
  6. Apply an exterior clear topcoat, like LIFELINE™ ADVANCE GLOSS or SATIN, to protect the color coat and add additional UV and mold and mildew protection.  Consider the Gloss for additional reflection of UV light.
  7. Fill all upward facing checks, cracks in wood, with a specialized acrylic sealant, like CHECK MATE 2™li>
  8. Clean the finish systems at least once a year with LOG WASH™, a liquid concentrate for bare wood and maintenance cleaning, to remove all foreign debris for the surface of the finish system and extend the its longevity.
  9. Perform an annual inspection of the coating system as a proactive maintenance approach.
    1. Darkening of the wood or finish when water is applied, an indication of water is getting through the coating and wetting the wood.
    2. Checks or micro-fissures in the wood, especially upward facing.
    3. Cracks in the finish.
    4. Color fading.
    5. Pay close attention to the south and west facing surfaces.
  10. Keep metal surface clean and freshly painted.  Salt spray is highly corrosive.

You can't completely stop or reverse the weathering of exterior wood, but you can slow the process dramatically by using the right type of finish system and a proactive game plan to combat the environmental elements.

sun graph
Last modified on Friday, 30 June 2017 17:44

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