Pressure-treated plywood is not completely waterproof, but it is designed to resist moisture damage under specific conditions.
Pressure-treated plywood is specifically treated with chemicals to enhance its durability by preventing insect damage and protecting against rot caused by moisture. According to the provided reference, it can survive outside without added protection if exposed only to average amounts of water like an occasional rainstorm or garden hose.
This indicates that while it is significantly more resistant to moisture-related issues like rot compared to untreated plywood, it is not impervious to water. Prolonged exposure to significant moisture, standing water, or constant wet conditions may still cause damage over time without additional sealing or protective measures.
Understanding Pressure Treatment and Water Resistance
The process of pressure treatment forces chemicals deep into the wood fibers. These chemicals are primarily designed to prevent fungal decay (rot) and insect infestation, which are common problems when wood is exposed to the elements.
However, the treatment does not make the wood impermeable to water. Wood is a natural, porous material, and even with treatment, it can still absorb water. The benefit of the treatment is that the absorbed water is less likely to cause rot and the wood is protected from wood-destroying insects.
Key Takeaways:
- Not Waterproof: Pressure-treated plywood is water-resistant, not waterproof.
- Resists Rot and Insects: Its primary purpose is protection against decay and pests, which are exacerbated by moisture.
- Handles Average Exposure: It can withstand occasional rain or watering without protection.
- May Need Sealing: For applications involving significant or continuous water exposure, additional sealing is recommended.
When Pressure Treated Plywood Holds Up
Based on the reference, pressure-treated plywood is suitable for outdoor use where it will encounter typical weather conditions:
- Siding (when properly installed and potentially sealed)
- Subflooring for decks or sheds
- Utility structures exposed to occasional rain
When Additional Protection is Needed
For maximum longevity and performance in very wet environments, consider additional steps:
- Applying a water sealant or repellent.
- Painting or staining the surface.
- Ensuring proper drainage.
In summary, pressure-treated plywood offers good resistance to the effects of moisture (rot and insects) under typical exposure levels, but it is not a substitute for a completely waterproof material or proper sealing in demanding wet conditions.
