Will Pressure Treated Wood Rot?

Pressure-treated wood is a marvel of modern construction. Wood has been treated with chemicals to resist decay, insects, and other natural threats. This treatment makes it popular for outdoor structures like decks, fences, and playground equipment. But what exactly is pressure-treated wood, and will it eventually rot?

Pressure-treated wood is lumber infused with chemicals to prevent rot and insect infestation. These chemicals, such as chromated copper arsenate (CCA), alkaline copper quaternary (ACQ), and copper azole, penetrate deep into the wood, providing long-lasting protection.

The importance of pressure-treated wood lies in its ability to withstand the harsh outdoor environment. It’s commonly used in applications where the wood is exposed to moisture, soil, and insects, such as in decks, fences, and retaining walls.

Understanding Wood Decay

Wood decay, or wood rot, is a natural process that breaks down the cellulose and lignin in wood. It’s caused by fungi, moisture, and sometimes insects. But how does it happen, and can pressure-treated wood succumb to decay? Wood decay is wood decomposition due to actions by certain species of fungi. Here’s a closer look at the process:

Causes of Decay:

  • Fungi: Decay fungi feed on the cellulose and lignin of wood, secreting enzymes that dissolve the wood cells. They require moisture content higher than 27% to 30% and temperatures between 77° F to 90° F to thrive.
  • Moisture: Water is essential for fungi to grow. Wood with a high moisture content is more susceptible to decay.
  • Insects: While insects like termites don’t cause decay, they are attracted to wood softened by rot.

Common Types of Wood Decay:

  • Brown Rot: Causes the wood to break down into brown cubes that split against the grain. It results in dry, powdery wood.
  • White Rot: Appears whitish and mushy, more common in hardwoods.
  • Dry Rot: A misnomer referring to decayed wood that has dried and ceased decaying.

Decay Prevention:

  • Use Decay-Resistant Species: Teak, rosewood, oak, redwood, cedar, etc.
  • Proper Grading: Prevent water from seeping under structures.
  • Ventilation: Adequate cross-ventilation in crawlspaces helps eliminate dead air pockets.
  • Vapor Barriers: Installing barriers like plastic sheets can limit evaporation and moisture condensation.

Preventing Rotting in Pressure-Treated Wood

Pressure-treated wood is a favorite for outdoor projects due to its enhanced durability and resistance to weather. However, it’s not completely immune to rot. Here’s a comprehensive guide to preventing rotting in pressure-treated wood, ensuring that your outdoor structures remain sturdy and attractive for years.

Proper Installation

  • Avoid Ground Contact: Ensure the wood isn’t in continuous contact with the ground or water-tended areas unless rated for such use.
  • Allow Drying Time: After purchasing pressure-treated wood, give it time to dry out before applying any paint or stain.


  • Use Moisture-Repelling Sealant: Sealing the wood with a moisture-repelling sealant prevents water from entering and reduces the chances of rotting.
  • Apply Deck Preservative: A deck preservative can protect from rot for pressure-treated decks. Stains, paints, and sealants are the best choices.
  • Regular Maintenance: Sealants must be applied at least once a year. A higher-grade sealant will result in longer protection, but cost can be a factor.


  • Regular Inspections: Regularly check for any signs of rot or decay, especially in damp areas or with less sun. Early identification can prevent extensive damage.
  • Promptly Address Exposed Areas: If there are screw or nail holes or any other form of exposed wood, promptly take care of them.
  • Use High-Quality Paints and Stains: Opt for high-quality, outdoor-rated stains or paints for pressure-treated wood.

Sealants and Coatings

  • Paint: Paint can help prevent wood rot by acting as a protective barrier between the wood and moisture. Exterior latex base paint is recommended.
  • Sealants: Products like waxes, oils, varnishes, and protecting sprays can enhance the longevity of treated wood.
  • Fire Retardant: Some protectors contain a fire retardant, adding an extra layer of safety.

Pressure Treated Wood in Specific Applications

Pressure-treated wood has revolutionized the construction industry, offering enhanced durability and resistance to decay. But how does it fare in specific applications like fence posts, outdoor structures, and underground usage?

Pressure-treated wood is a popular choice for fence posts due to its resistance to rot and insects. However, it’s not invincible:

  • Installation Method: Proper installation is crucial. Posts should be set in concrete to prevent ground contact, which can lead to decay.
  • Type of Wood: Using the right type of pressure-treated wood, rated for ground contact, can prolong the life of fence posts.
  • Maintenance: Regular inspection and sealing can prevent decay.

Outdoor Structures

From decks to pergolas, pressure-treated wood is widely used in outdoor structures:

  • Material Choices: Pressure-treated wood offers easy workability and takes stains and waterproofing easily. However, it can corrode unprotected metal fasteners and connectors.
  • Durability Concerns: Boards can warp and crack, requiring frequent cleaning, resealing, and restaining.
  • Design Considerations: Proper drainage, spacing, and support are essential to prevent water accumulation and potential rot.

Underground Usage

Pressure-treated wood can be used underground, but special considerations must be taken:

  • Ground Contact: Wood in contact with the ground or buried must be specially treated for such use to prevent decay.
  • Moisture Concerns: Underground usage exposes wood to constant moisture, increasing the risk of rot. Proper sealing and the use of moisture barriers can mitigate this risk.
  • Longevity: Even with proper treatment, pressure-treated wood underground may have a limited lifespan compared to other materials.

Decay Patterns and Post Installation

Understanding the decay patterns and proper post installation can enhance the lifespan of pressure-treated wood:

  • Decay Patterns: Wood decay usually starts when the wood is in contact with moisture or soil. Regular inspection can identify early signs of decay.
  • Post Installation: Proper installation, including concrete footings and moisture barriers, can prevent decay in fence posts and other vertical structures.

Enhancing Appearance and Durability

Pressure-treated wood is renowned for its durability and resistance to rot, but its appearance and longevity can be further enhanced through proper staining and long-term care.

Staining Methods

Staining pressure-treated wood slightly differs from staining untreated wood, but the process is straightforward. Here’s a step-by-step guide:

  1. Choose the Right Stain: Selecting the right stain for pressure-treated wood is crucial. Consider the overall theme of your deck and outdoor space, and choose a stain color that complements the surroundings. Neutral wood stain colors that blend with any background or décor are often preferred.
  2. Clean the Wood: Clean the pressure-treated wood thoroughly before staining. Use an approved wooden deck cleaner like Olympic Premium Deck Cleaner to remove dirt, mildew, algae, pollen, or mold. Scrub with a stiff-bristled mop and wash away the residue with a pressure washer.
  3. Apply the Stain: Depending on the type of stain you’re using, the application method may vary:
  • Clear Wood Sealant, Wood Toner, or Semi-Transparent Deck Stain: Apply one thin coat with a high-quality brush or sprayer.
  • Solid Color Deck Stains: Apply two thin coats with a paint brush or roller, keeping a wet edge to avoid lap marks.
  1. Backbrushing: This technique ensures that all parts of the wood, including joints, edges, seams, and ends, get the same coverage of wood stain. Push the stain-coated brush between each board, ensuring no areas are visibly uncolored by the stain product.
  2. Allow to Dry: Let the pressure-treated wood dry fully before moving any furniture onto the surface of the deck or patio.

Choosing Stains

  • Wood Stain Colors: Choose colors that match other exterior wood surfaces, like sheds or patio furniture.
  • Type of Stain: Consider clear wood sealants, toners, semi-transparent deck stains, or solid color stains based on the desired appearance and protection level.

Long-Term Care

  • Regular Maintenance: Periodically reapply the stain to maintain the appearance and protection.
  • Inspection: Regularly inspect for signs of wear or damage and address them promptly.

Types of Stains and Application Techniques

  • Clear Wood Sealant: Offers a natural look while providing protection.
  • Wood Toner: A slight tint enhances the wood’s natural beauty.
  • Semi-Transparent Deck Stain: Provides color while allowing the wood grain to show through.
  • Solid Color Deck Stains: Offers the most protection and color, hiding the wood grain.

Additional Considerations with Pressure Treated Wood

Pressure-treated wood is a popular choice for various applications but comes with challenges and concerns.

Warping and Shrinking

  • Cracking and Splitting: Pressure-treated wood can absorb and release moisture, leading to splitting and cracking over time. This can affect both appearance and performance.
  • Cupping and Warping: The wood may experience movement in cupping, bowing, and twisting, which warps the wood. Depending on the wood, this can be subtle or dramatic; once it occurs, it’s challenging to correct.


  • Density and Buoyancy: Pressure-treated wood’s density can vary, affecting its buoyancy. While it generally doesn’t float like untreated wood, specific applications and treatments may alter this behavior.

Turning Grey

  • Discoloration: Over time, pressure-treated wood may turn grey due to exposure to sunlight and weather. This natural process can be mitigated with proper sealing and staining.


  • Mold and Mildew Growth: Pressure-treated wood can still be susceptible to mold and mildew if not properly maintained. Regular cleaning and the application of anti-mold treatments can prevent this issue.

Environmental Factors

  • Chemical Leaching: The chemicals used in pressure-treated wood can leach into soil and water, potentially affecting the environment. Newer treatments are considered less hazardous, but concerns remain.

Other Considerations

  • Corroding of Non-Galvanized Metal: The chemicals in pressure-treated wood can react with non-galvanized metals, causing corrosion. Using galvanized metal can prevent this issue.
  • Not Designed for Finish Work: Pressure-treated wood often has a greenish tone due to the chemicals used, requiring priming and painting for finish surfaces.


Pressure-treated wood is a popular choice for construction and outdoor projects due to its durability and resistance to rot. However, its performance can be influenced by factors like installation, maintenance, and environmental conditions. To maximize its benefits, homeowners and builders should follow best practices for preventing rot and caring for pressure-treated wood. A holistic approach, considering selection, installation, staining, and long-term maintenance, ensures that pressure-treated wood remains a lasting and beautiful addition to any outdoor space.