Surface Preparation and Gray Wood
When working on older properties the durability of the old growth lumber used to fabricate the architectural elements is superior to lumber available today.
As this quality material gets exposed to the elements of sun and moisture the exposed surface begins to show signs of surface mold, graying and checking.
Paint failure and exposed gray wood fibers. No wood decay is present.
Wood consists of lignin and cellulose fibers. When the wood is exposed to light the lignin breaks down and causes the cellulose fibers to break away.
Wood is like a bundle of straws held together with glue. The straws are the cellulose fiber, the glue is the lignin.
A cross-section of wood cellulose fibers
Before conducting epoxy repairs or painting the surface it is necessary to remove all gray wood ( and any wood decay ). Failure to do so will compromise a solid bond to a sound substrate.
As the paint dries it undergoes a process called coalescing. This process creates stress on the substrate and pulls away loose paint and wood fibers. The sloughing of the damaged wood fibers results in paint failure.
Paint failure due to the sloughing off of gray wood.
( Note the gray wood fibers adhering to the underside of the failed paint film )
Removing failed paint and sanding to bright wood is the only way to insure a solid bond to wood and provide a long lasting repair.
Old window sash sanded to bright, uneffected wood