Cracking of rough-sawn siding
 
Cause

The most common surface to show this failure is plywood that has been stained with a semi-transparent or solid color alkyd stain. The reasons for plywood separation are the same as those discussed in “Plywood Cracking”, as they relate to moisture content, method of plywood manufacture and induced wood stress. The main difference is that although the coating cracks, it does not peel and lead to flaking. Instead, the wood is open for moisture intrusion from outside weather conditions, leading to delamination and deterioration of the plywood.

The wood is highly textured, allowing water to remain on the total surface for extended time periods. These woods are designed for staining and since plywood cracking is inevitable, the life of the coating is shortened. Pigmented stains penetrate the porous wood surface, allowing very little of the stain to remain on the surface. Subsequently, as the wood cracks, the applied stain also cracks.
 
Solution

Using detergent and water, scrub siding to remove old oxidized paint film, dirt and other contaminants. Flush with clean water and allow to dry thoroughly. Fill large holes found in plywood grooves with colored caulk to prevent further water intrusion.
 

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