6 Exterior Painting Procedures for Cracking Plywood Surfaces

One exterior painting concern facing many homeowners is the hairline cracks in the paint on plywood surfaces. Most builders have used plenty of plywood in the construction of homes today. Plywood is a durable and strong material, but there are some problems that can develop in plywood overtime. It is prone to cracking at the surface level. The hairline cracks that develop in plywood is called checking in the exterior painting industry.

Checking usually occurs on the outer veneer of a plywood surface that is exposed to sunlight and weather. As the plywood outer veneer ages, it cracks along the grain line of the veneer from repeated expansion and contraction. As the separation in the grain occurs it causes the painted surface to check.

One exterior painting question frequently asked is how to properly treat areas where checking is occurring. That usually depends on how bad the checking is. It's possible you may need to replace the plywood if the cracking is bad enough and if that area is getting a lot of sunlight, temperature and moisture exposure. However, I would try the following process first before deciding to replace the plywood.

1.The first step is to sand the entire areas with a power sander to remove oxidation and smooth the surface.

2.Fill all holes, cracks and seams with a good grade of caulk.

3.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.

4.After the Zinsser Peel Stop undercoat has dried thoroughly, apply two layers of a good grade of outside house 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.

5.In cases where the plywood is extremely aged, you may need to replace the wood completely.

6.If new plywood is mounted, you can prevent it from checking by sanding the surface of the new plywood smooth and follow the same steps above.

One thing to remember is that paint elasticity is important for enduring the movement along the grain of 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.

You should keep this exterior painting tip in mind. 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.