Even though contemporary plywood was patented in the mid 1800’s, it only came to exteriors use by 1934. And today, the builders can choose from different ranges of plywood according to the uses and also take into consideration some factors like the budget.
Before we get to know which plywood is suitable for outdoor use, we will first study what exactly is the exterior plywood and the difference between interior and exterior plywood. The major difference is that exterior plywood can be used for both interiors and exteriors but interior plywoods are strictly not meant for exterior plywood. You cannot just look into it and tell the difference therefore, you’ll have to get it purchased properly mentioning the purpose. Since exterior plywood needs to appear good looking, it must be resistant to moisture and rot. Looks and durability matters!
Well, plywood is of two types, exterior and interior for outdoor and indoor respectively, but then even the outdoor plywood has different types. Let us study that too.
CDX is the most commonly used outdoor plywood. It has got ¾.⅝ and ½ thickness. They have best for cabinet grades as well as construction grades.
Next comes Marine grade with knot free sheets core that resists the formation of water pockets within the structure.
Then you have Pressure treated plywood which comes with a greenish hue and a light oily surface. This is manufactured by infusing regular plywood with chemicals under pressure to make it extra resistant to mold mildew.
Next is Oriented Strand Board plywood, which comes as a substitute for sheathing and roof decking. This one is cheaper and available almost everywhere. It is made with waterproof glue and is best when semi exposed to the elements because it is covered by siding or roofing.
T1-11 is the next and is used for siding. This can be easily painted to match the color scheme and has a rough sawn appearance.
X grade is the best for any outdoor application, but incase if your budget doesn’t corporate choose CDX. For Ground contact and horizontal installations prefer Pressure-treated plywood. And for underwater requirements, you only need the expensive but the only appropriate, Marine grade. And for decorative purposes such as siding, you may use T1-11.
One thing to always keep in mind is that, your requirement and budget are what decides the exterior plywood you must choose.