To line pressure-treated wood, particularly when used for structures like raised garden beds, you can line the inside with heavy plastic to create a barrier.
Lining pressure-treated wood is a common practice, especially in gardening and landscaping projects, primarily to prevent potential chemicals within the wood from migrating into the surrounding soil or environment. This creates a protective layer between the treated wood and the contents it holds or the ground it is near.
Why Line Pressure-Treated Wood?
Pressure-treated lumber contains chemicals that protect the wood from rot and insects, extending its lifespan. While modern treatments are considered safer than older ones (like those using Chromated Copper Arsenate or CCA), some people choose to create a barrier as a precaution. The main reasons for lining include:
- Preventing Chemical Leaching: The primary reason is to prevent the chemicals used in the treatment process from leaching out of the wood and into the soil, particularly in vegetable gardens where the soil is used for growing food.
- Extending Wood Life (Indirectly): While the wood is treated, lining can help keep the inside surface drier by preventing direct contact with damp soil, potentially further reducing wear and tear.
How to Line with Heavy Plastic
Based on common practice and the provided reference, lining pressure-treated wood, especially for garden beds, is effectively done using heavy plastic.
- Choose the Right Material: Use a heavy plastic sheeting. Options include:
- Pond liner material
- Thick construction-grade plastic sheeting (e.g., 6-mil or thicker)
- Specific garden bed liners
- Prepare the Surface: Ensure the inside surfaces of the pressure-treated wood are relatively clean and free from sharp points that could puncture the plastic.
- Cut the Plastic: Cut the plastic sheeting to size, ensuring it is large enough to cover the inside walls of the structure (like a garden bed) with some overlap at the top edge.
- Install the Liner:
- Place the plastic inside the structure, pressing it against the inner walls.
- Smooth it out, removing wrinkles as much as possible.
- Bring the top edge of the plastic up and over the top edge of the wood.
- Secure the plastic in place. You can use staples along the outside face just below the top edge, or trap the plastic under a cap piece of lumber.
- Consider Drainage: While the plastic prevents leaching, it also holds moisture. For structures like garden beds, ensure the bottom is open to the ground or that you incorporate drainage holes if the base is also lined or sits on an impermeable surface. Do not line the bottom of a garden bed if it sits directly on the soil you intend to grow in.
- Add a Protective Top (Optional but Recommended): As mentioned in the reference, consider adding a layer of untreated lumber boards on top of the pressure-treated wood structure. This creates a flat top surface that can be used for sitting and, crucially, to avoid contact with the treated wood, which is particularly important if you have CCA-treated wood in your garden.
Materials Summary
Here's a quick look at the key materials involved:
| Purpose | Material Used | Notes |
|---|---|---|
| Barrier against leaching | Heavy Plastic Sheeting | Pond liner, 6-mil plastic, etc. |
| Structural frame | Pressure-Treated Wood | The material being lined. |
| Optional protective cap | Untreated Lumber Boards | Added to the top edge to avoid contact. |
By lining the inside of the structure with heavy plastic, you effectively create a barrier that isolates the pressure-treated wood from the soil or other contents within the bed, preventing the leaching of chemicals as described in the provided reference.
