Solving Exterior Paint Problems Associated With Cracking Plywood

 Do you use Plywood in the trim areas on your home? Is the exterior paint on your home cracking where it was applied over it? Many homes built today have plywood for certain trim areas. Although Plywood is a durable material, it does has one drawback. It is prone to cracking at the surface level along the grain line. Cracking of exterior paint along plywood’s grain line is called checking in the exterior painting industry.
When exposed to sunlight, temperature changes and moisture plywood surface starts to weather. Checking usually occurs because the outer veneer of a plywood. As the plywood outer veneer weathers, it separates along the grain line of the veneer from repeated expansion and contraction. As the cracks in the grain occur, it causes the painted surface to check.
So how do you properly treat areas where checking is occurring? That usually depends on how bad the checking is. First evaluate how much sunlight, temperature and moisture exposure the plywood is getting. The cracking along the grain line could be bad enough to warrant just replacing the plywood if exposure is high. However, I would try the following process first before deciding to replace the plywood

• Smooth and remove oxidation by sanding the entire checked area with a power sander.
• Fill all cracks and seams with a good grade of caulk. Smooth out the caulk.
• After the sanding is complete and all cracks are filled with caulk, prime the bare wood with two coats of Zinsser Peel Stop. Peel Stop is a very elastic primer that can withstand the expansion and contraction of the cracks in the plywood without separating. This elastic base coat is very important in order to withstand the movement in the veneer layer of the plywood along the grain line.
• Once the Zinsser Peel Stop undercoat has dried thoroughly, apply two layers of a Duration Lifetime Paint. My preference for the top coat is Sherwin Williams’s exterior Duration paint. Duration has 70 percent more elasticity than your average 25 year paint and will stretch without separating along the grain line of the plywood veneer.
• If new plywood is mounted, you need to protect it by sanding the surface of the new plywood smooth and follow the same painting steps above.

Keep in mind that elasticity of exterior paint is extremely important for plywood surfaces. Oil base paint and primers don’t have enough elasticity built into their formulas to handle the checking that will occur when plywood is subject to sunlight, moisture, and ever changing temperatures.
Another thing you should keep in mind is that thickness of paint film is very important. I recommend the 4 coats above (2 coats of Peel Stop and 2 Coats of Duration) because a thicker film of paint will stretch further without cracking.