Is CDX plywood rated for permanent exterior use?
No. CDX carries Exposure 1 glue, which is rated for construction-stage moisture — not permanent outdoor exposure. For long-term exterior use, step up to BC, ACX, or HDO/MDO depending on the finish required.
What's the difference between Exposure 1 and Exterior-rated plywood?
Both use water-resistant exterior adhesives, but Exterior-rated panels also carry veneer grades suitable for long-term weather exposure. Exposure 1 panels are designed to survive weather during construction, not permanent exterior service.
When should I specify marine plywood instead of ACX?
Specify marine only when void-free core construction genuinely matters — boat hulls, transoms, below-waterline cabinetry. For decks and outdoor projects without continuous water contact, ACX or film-faced formwork plywood deliver the same exterior-rated bond at lower cost.
Is HDO plywood suitable for outdoor signage?
MDO is the standard for exterior painted signage because its overlay holds paint longer than raw veneer. HDO is typically reserved for concrete formwork where the denser overlay resists abrasion from concrete. Either is exterior-rated, but MDO is the sign-industry default.
How do I verify a plywood panel is genuinely exterior-rated?
Four checks: confirm the glue type (WBP phenolic for Class 3 / EN 636-3; WBP melamine for Class 2 / EN 636-2), verify the APA or EN stamp is authentic, ask for recent EN 314-2 boil-test results or APA-equivalent data, and confirm the supplier's ISO 9001, FSC, and (for U.S. imports) CARB P2 certifications.
What's the difference between EN 636-2 and EN 636-3 plywood?
EN 636-2 (Class 2) panels are rated for humid conditions and occasional short-term exterior exposure — typically using WBP melamine adhesive. EN 636-3 (Class 3) panels use WBP phenolic adhesive and are rated for full exterior service including permanent weather exposure.
