When it comes to 4×4 wood posts used for fencing, decking, landscaping and other outdoor structures, treatment is crucial for longevity and rot resistance. However, not all 4×4 posts on the market are treated, so it’s important for consumers to understand the differences.
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What is Treatment for 4×4 Posts?
Treatment involves impregnating the wood with chemical preservatives that protect against fungal decay, insect damage and other biological threats. The preservatives are applied under pressure in a process known as pressure-treating. This forces the chemicals deep into the cellular structure of the wood for maximum protection.
The most common preservative chemicals used today are:
- Chromated copper arsenate (CCA) – a mix of chromium, copper and arsenic salts
- Alkaline copper quaternary (ACQ) – a mix of copper and quaternary ammonium compounds
- Copper azole (CA) – a mix of copper and tebuconazole fungicide
These preservative treatments allow 4×4 posts to last for decades, even when buried in ground contact applications. Untreated posts, on the other hand, will quickly decay and degrade when exposed to common outdoor conditions.
Grades of Treated 4×4 Posts
Not all treated 4×4 posts offer the same level of protection. The amount of chemical retention, or concentration of preservatives, can vary based on the desired application or environmental conditions. Here are the common grades:
| Treatment Level | Description |
|---|---|
| Above Ground (AG) or Ground Contact General Use (GC-General) | Lowest treatment level, for posts used in above ground applications like fences and decking. Not rated for ground contact. |
| Ground Contact Heavy Duty (GC-Heavy) | Medium treatment level, for fence posts and landscaping timbers with partial ground contact. Not rated for permanent ground contact. |
| Ground Contact Extra Heavy Duty (GC-Extra) | Highest treatment level, meets requirements for full, permanent ground contact such as structural posts. |
Higher treatment levels have more complete penetration and higher retention of preservatives in the outer zones of the wood. This added protection comes at a higher cost, so it’s important to match the appropriate grade to the intended use.
Are All 4×4 Posts Treated?
Now we can address the key question – are all 4×4 posts treated? The short answer is no. Here are some examples of untreated 4×4 lumber that is commonly available:
- Whitewood – This refers to inexpensive, untreated spruce-pine-fir or hem-fir posts. May also be called “green” 4x4s. Offers no rot resistance.
- Cedar – Posts cut from Western Red Cedar contain natural decay-resistant oils. However, untreated cedar still only lasts about 5-7 years in ground contact.
- Redwood – Like cedar, untreated redwood posts have some natural rot resistance but still only last 5-10 years in ground contact applications.
While these untreated 4×4 post options are lower cost up front, they will succumb to rot and need frequent replacing. This ends up being more expensive compared to treated posts that last for decades.
Identifying Treated 4x4s
When shopping for 4×4 posts, look for key signs that indicate proper treatment:
- Dark green or brown coloration throughout the post. Untreated whitewood will be pale yellow/white.
- Stamps from the treatment company with information like the retention level and preservative type.
- End tags on each post summarizing the treatment specs.
- Look for common treated wood brand names like YellaWood, Wolmanized, Preserve, NatureWood, Natural Select.
Shoppers should be wary of 4×4 posts that are unlabeled or lack the clear markings of treated lumber. Some deceitful suppliers may try to pass off untreated 4x4s as treated.
Choosing the Right Treated 4x4s
When selecting treated 4×4 posts, match the retention level to your specific project needs:
- Use Ground Contact Heavy Duty posts for fence posts, mailbox posts, or raised garden beds.
- Choose Ground Contact Extra Heavy Duty for structural applications like deck supports, retaining walls, or permanent sign posts.
- Above Ground treated posts are only suitable for applications like fences, rails, or benches where the posts will stay above soil.
Even properly treated 4x4s will eventually require replacement, but should last 30+ years for fence posts and 50+ years for critical structural supports. Taking the time to select the right level of treatment will maximize longevity and performance.
Pressure Treating Options for Untreated 4x4s
If you’ve already purchased untreated 4×4 posts or have access to low-cost whitewood, you may consider having them pressure treated after the fact. Many treatment companies offer custom processing services for posts, lumber and timbers.
Benefits of post-treatment include:
- Choose the exact retention level you need for the project.
- Often cheaper than buying pre-treated posts.
- Control over wood species, size and quality.
- May be required for code approvals in structural applications.
Be sure to factor in the cost of transportation and processing if going the after-treatment route. Lead times can also be 4-6 weeks or more. Overall it gives flexibility if you have immediate access to quality inexpensive 4x4s.
Use of Preservative-Free Options
While pressure-treated posts are recommended for most outdoor projects, there are a few scenarios where untreated or preservative-free options make sense:
- Raised beds – Untreated cedar or redwood allow safe contact with edible plants.
- Temporary structures – Like garden stakes that will be replaced annually.
- Interior applications – Untreated whitewood posts are fine for indoor use.
- Preservative sensitivity – Those with chemical sensitivity may choose untreated wood.
Even in these cases, care should be taken to reduce ground contact and moisture exposure wherever possible. Limiting the post end buried in soil and providing a drainage base are good preventative measures.
Disposal and Recycling of Treated 4x4s
When treated 4×4 posts reach the end of their service life, they require special handling for disposal or recycling due to the presence of preservative chemicals:
- Contact your local waste management facility. Some accept treated wood in designated areas.
- Reuse for non-critical projects if still in sound condition.
- Follow procedures for hazardous waste if required in your region.
- Never burn treated wood, as toxic fumes can be released.
With proper disposal, treated 4x4s posts pose minimal environmental impact and health risks. The small amounts of preservatives leach out slowly over decades of service. Always wear gloves and respiratory protection when handling old treated lumber.
Conclusion
When buying 4×4 posts for outdoor structures, opting for pressure-treated wood that has been properly impregnated with rot-resistant preservative chemicals is the only way to ensure decades of reliable service life. While untreated 4x4s are cheaper up front, their rapid decay in ground contact makes them a poor long-term investment. Taking the time to identify posts that have been adequately treated for their intended use will provide maximum value and avoid premature replacement costs down the road.