One of the most common complaints that occur is peeling on exterior wood or hardboard siding. Although there are many possible causes for paint peeling, in most cases, the paint is not the culprit behind the failure. The most common cause is wood delamination.

Wood delamination is caused by a breakdown of the cellular structure of the wood. This can be attributed to moisture in the wood that allows fungi to grow and feed off the starches and sugars present. Fungi are microscopic spores that travel in the air. The spores float in the air until they either fall back to the ground or attach to a moist surface. Most wood surfaces provide an ideal environment for fungi to grow and germinate. Over time the fungi cause the cellular structure of the wood to break down. As the moisture in the wood tries to exit, the top layer of the wood fibers break down and separate. When this occurs, the bond between the base coat and the structure is broken and loss of adhesion occurs.

To look for wood delamination when you are making a site inspection, look for particles of wood on the back of the peeling samples. A magnifying glass can aid in determining if wood or wood fibers are present. The back of the peeled paint may be completely covered or only partially covered with wood fibers from the substrate.

To correct the problem, the source of moisture must be located and eliminated. There are a variety of ways moisture can reach painted wood substrates. Among these are uncaulked joints, cracked caulking, and moisture-laden air trapped in the building, damp basements, vegetation close to the wood and painting over damp wood. Many times power washing is used as a surface preparation. It is important to remember that there must be sufficient drying before painting.

Once the source of moisture has been eliminated, all areas affected should be scraped and sanded to remove the loose paint. The bare wood should be sanded to a new wood look to remove all loose fibers and grayed wood. The bare wood should then be alkyd primed and top coated with the desired finish.

By making a site visit, it should be possible to determine that wood delamination is the mode of failure. This will allow you to give your customer a cause and solution to the problem.

Source: Remson Nichols Southeast Division

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