How to Keep Pressure-Treated Wood from Warping?
Are you tired of seeing your beautifully crafted outdoor project made from pressure-treated (PT) wood twist and warp?
We understand your frustration. PT wood is an excellent choice for outdoor projects due to its resistance to rot and decay, but it comes with a significant downside of warping.
There’s nothing worse than spending time and money on a PT wood project, only to have it warp and twist before your eyes.
And for beginner or intermediate woodworkers, preventing wood warping issues can be particularly challenging.
But don’t fret! In this informative blog post, we’ll delve into why PT wood warps and most importantly, reveal how to prevent it.
We’ll equip you with the knowledge and tools you need to ensure your PT wood projects remain flat and sturdy for years to come.
So, get ready to learn and bid farewell to those pesky warping woes! With our expert tips, you can now confidently take on any PT wood project without fear of unsightly warping.
What is Pressure Treated Wood, and Does it Warp?
Pressure-treated (PT) wood is a type of lumber treated with chemicals to resist rot, decay, and insect infestation.
Pressure-treating wood usually involves soaking the lumber in a solution of water and chemicals, then pressurizing it to force the chemicals into the wood.
Most people don’t know that pressure-treated wood can warp out of shape if it’s not properly sealed, handled, and stored. And if you have used warped wood before, you know it’s hard to get it to lay flat.
Even worse, If PT wood warps when a project is completed, it can actually cause problems for your customers down the road.
In this regard, if you’re using PT lumber, you need to take steps to prevent it from warping; otherwise, you may be in for a world of hurt down the road.
What causes Pressure Treated Wood to Warp?
The average moisture content of pressure-treated wood used for construction is usually 15-19%. When the wood is stored, it loses most of this moisture to match the ambient moisture (equilibrium moisture content).
Tip: You can invest in a moisture meter if you want to keep track of the moisture level of your pressure-treated wood.
When pressure-treated dries up, it first loses free water, which is typically water in hollow spaces inside the word structure. After that, the wood loses molecular water (bound water), which is the water bound in the fiber structure of the wood cells.
Warping occurs when bound water falls below fiber saturation level. Past the fiber saturation level, the wood fibers expand or contract when there’s a drastic and uneven change in the moisture content of the wood fibers.
In this regard, the common cause of wood warping is uneven contraction and expansion of wood fibers when exposed to extreme temperature and humidity changes.
Types of Wood Warps
There are four types of wood warps: bowing, crooking, cupping and twisting. If you’ve ever seen a pressure-treated piece of wood curved or twisted, it’s likely one of these warps.
Here is a closer look at each of these types of wood warping.
Bow warping
A bow warp is a warp along the face of the wood. If you look at a board from the end, you would see that the warp bends the board into a “U” shape.
Crook warping
A crook warp is a warp that runs along the edge of a wood plank. Crook warps are especially common in long, thin boards.
Cup warping
Warping across the width of the wood face is known as cup warping. The edges are raised or lowered in relation to the center.
Twist warping
A twist warp is a spiral distortion in which the two ends of the wood don’t lie on the same plane.
Twist warps can be very difficult to correct. The only way to fix the problem is to cut the wood along its length and realign the two halves.
Warping is also likely to occur in other places on PT wood, such as:
Center of the tree
Because the tree’s center dries last, wood sourced from the center of a tree is more likely to warp when used.
Dark stripe
Warping can also occur in a dark stripe. A dark stripe is a line of cells that are darker than the surrounding cells. This is caused by a difference in the thickness of the cell walls. When the cell walls are thinner, they are more likely to warp.
Big knots
Big knots can also cause warping. This is because knots are areas of the tree where the wood is condensed. When the wood is condensed, it is more likely to warp.
Note:
- If the wood was cut with the grain (saw kerf parallel to the grain), it’s more likely to warp than if it was cut across the grain (saw kerf perpendicular to the grain).
- The type of wood also affects the amount of warp. Warp is more likely to occur in softwoods than in hardwoods.
Strategies to Prevent Pressure-Treated Wood from Warping
| Method | Description |
|---|---|
| Store in a cool, shady area | Pressure-treated wood is susceptible to warping and cracking when exposed to extreme heat and direct sunlight. Store the wood in a cool, shady area away from direct sunlight to avoid drying out too quickly and warping. If leaving the wood in the sun, cover it with a tarp or other protective material. |
| Keep wood in the same area it will be used | Pressure-treated wood is hygroscopic and will absorb or release moisture until it reaches equilibrium with its surroundings. Keep the wood in the same area it will be used to avoid cases of warping. |
| Avoid leaving in rain or heavy dampness | Warping is more likely to happen when pressure-treated wood is left in the rain or heavy dampness. Avoid these conditions by storing the wood inside or at least covered. |
| Dry on a flat surface | Drying pressure-treated wood on a flat surface promotes even weight and moisture distribution, preventing warping as it dries. Use a table, floor, or plywood surface ensuring it is completely flat. |
| Don’t store pieces on top of each other | When storing several pieces of pressure-treated wood, do not stack them on top of each other. Leave spaces in between to promote airflow and prevent warping due to uneven drying. |
| Weight the lumber on the ends and center during storage | Weighting the lumber using bricks or other wood blocks prevents it from warping as it dries. Stack the bricks on top of the lumber, evenly distributing them between the ends and center. |
| Clamp the wood on the workbench | When not continuously working on the pressure-treated wood, clamp it in place to prevent movement that could lead to warping. Ensure the clamps are tight enough to hold the wood in place. |
| Pick a wider piece of wood | Wider pieces of pressure-treated wood are less likely to warp than narrower ones since they have more cells that can expand and contract more without causing warping. |
| Stain the pressure-treated wood | Staining pressure-treated wood creates a barrier that helps keep moisture out, reducing the chances of warping, especially in high humidity environments. Stain binds the fibers together, keeping moisture levels even and reducing instances of warping. |
| Use a dehumidifier in the storage room | High humidity levels in the storage room can cause pressure-treated wood to absorb moisture from the air unevenly, leading to warping. Use a dehumidifier to reduce the risk of warping by decreasing the amount of moisture in the air. |
| Store pressure-treated plywood vertically | Storing pressure-treated plywood vertically reduces the risk of warping by allowing the veneer layers to expand and contract evenly. Additionally, the wood fibers are less likely to absorb moisture when stored vertically. Store in a climate-controlled environment. |
How to Straighten Warped Pressure Treated Wood?
If you do have warped wood, there are a few ways to try to fix it:
One method is to apply pressure to the warped area. This can be done with a heavy object like a stack of blocks or a bag of sand.
If you have pressure-treated lumber that has warped slightly, you can try to straighten it out by ironing the warped area:
- First, ensure the wood is dry and free of any moisture.
- Next, place a clean cloth over the warped area and use an iron on the warm setting to press down on the cloth.
- Press for several minutes, then check to see if the wood has straightened.
- If the wood is still warped, repeat the steps one more time.
If these methods don’t work, you can try using a jack plane to remove some of the material from the warped area. This will make the PT wood thinner and hopefully straighten it out.
That said, it’s often difficult to fix warped pressure-treated wood, so it’s best to avoid the problem in the first place.
What to Do with Warped Wood That Can’t Be Fixed?
So you’ve got a piece of pressure-treated wood that’s warped, and you’re not sure what to do with it. You’ve tried everything to fix it, but nothing seems to work. Well, don’t give up just yet! There are still a few things you can do with your warped wood.
One option is to use it as is. Warped wood can actually add character to a piece of furniture or decoration. So if you’re looking for a rustic look, then your warped wood may be perfect for you.
Another option is to cut it up and use it for smaller projects. You can use it for things like picture frames, coasters, or even jewelry.
And finally, if you’re really not sure what to do with your warped wood, you can always shape the warpage to make interesting art pieces.
Wrapping Up
Pressure-treated wood is a great way to keep your deck or porch looking new for years. But who would have thought that pressure-treated wood could warp out of shape?
I certainly didn’t. But apparently, it’s a thing. If you don’t properly seal, handle, and store PT wood, it can warp out of shape.
The tips discussed in this post will help keep your pressure-treated wood from warping and ensure a long lifespan for your project. Fortunately, you also now know what to do with warped PT lumber if it can’t be corrected.