How to Keep Pressure-Treated Wood from Warping?

We all know that pressure-treated (PT) wood is great for outdoor projects because it resists rot and decay. But did you know that PT wood is prone to warping?

Certainly, 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 a beginner or intermediate woodworker, it can be a challenge to determine how to really avoid wood warping problems.

But worry out. In this blog post, we’ll explain why PT wood warps and, most importantly, how to prevent it.

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.

Methods to Prevent Pressure Treated Wood from Warping

Don’t leave the wood in the hot sun

Wood is a natural material that is susceptible to warping and cracking when exposed to extreme heat and direct sunlight.

If you leave your pressure-treated wood in the hot sun for extended periods, it will dry out too quickly and warp or crack as a result.

To avoid this, store your wood in a cool, shady area away from direct sunlight. If you must leave the wood in the sun, cover it with a tarp or other protective material to prevent it from drying out too quickly.

Keep wood in the same area it’ll be used

Wood is hygroscopic, meaning it will absorb or release moisture until it reaches equilibrium with its surroundings.

For this reason, it’s crucial to keep pressure-treated wood in the same area it will be used, as it will get used to the moisture content there and avoid cases of warping.

Don’t leave PT wood in the rain or heavy dampness

Warping is more likely to happen when the wood is left in the rain or heavy dampness, so if you can avoid those conditions, you’ll be less likely to have warped wood.

Again, it’s a good idea to keep wood you’re not using inside, or at least covered, to prevent it from warping.

Dry your wood on a flat surface

One of the best ways to dry your pressure-treated wood is to use a flat surface.

This will cause even weight and moisture distribution and, in turn, prevent your wood from warping as it dries. You can use a table, a floor, or even a piece of plywood. Just make sure that the surface is completely flat.

Don’t store pieces of wood on top of each other

If you’re storing several pieces of pressure wood, it’s important not to stack them on top of each other.

Instead, leave spaces in between the pieces to promote airflow. This will help prevent warping due to uneven drying.

Weight the lumber on the ends and center during storage

Warping is caused by the lumber shrinking or expanding as it dries out, so by weighting the lumber, you’re essentially keeping it in place, so it doesn’t have a chance to warp.

There are a few different ways you can weigh the lumber, but the most common is to use bricks or other wood blocks.

Just stack the bricks on top of the lumber, evenly distributing them between the ends and center. This will help keep the PT lumber stable and prevent warping.

Clamp your wood on the workbench

When you’re not continuously working on your pressure-treated wood, you want to make sure you’re clamping it to prevent the wood from moving.

You also want to make sure that the clamps are tight enough so that they’re actually holding the wood in place.

If the clamps are too loose, the wood will be able to move and warp.

Pick a wider piece of wood

It’s true that wider wood pieces are less likely to warp than narrower ones, and it all has to do with the way that wood is composed.

Wood is made up of individual cells, and these cells are filled with water. The cells expand and contract when the wood is exposed to heat or moisture. This expansion and contraction are what cause the wood to warp.

However, wider boards have more cells than narrower boards. This means they can expand and contract more without causing the board to warp.

So, if you want to avoid warped wood, go for wider boards instead of narrower ones.

Stain your pressure-treated wood

Staining is an essential part of protecting your PT wood from the elements. When you stain your wood, you create a barrier that helps keep moisture out.

wood staining

This is especially important in areas where the wood is more likely to warp, such as in high humidity environments. By staining your wood, you can help to reduce the chances of warping and make your wood last longer.

What’s more, the stain you use on your PT lumber seeps into the pores and fibers of the wood.

This binds the fibers together and helps keep the moisture levels even, reducing the instances of warping.

Use a dehumidifier in the room where you store wood

Warping is likely to happen when the humidity in the storage room is too high.

This is because the wood can absorb the moisture from the air unevenly, leading to uneven contraction and expansion of wood fibers.

Dehumidifiers can help reduce the risk of warping by decreasing the amount of moisture in the air.

When choosing a dehumidifier for your wood storage room, be sure to get one that is the right size for the space.

You’ll also want to ensure that the dehumidifier has a built-in humidistat so that it can maintain the proper humidity level in the room.

Store pressure-treated plywood vertically

When plywood is stored vertically, the veneer layers expand and contract evenly, reducing the risk of warping.

Additionally, when stored vertically, the wood fibers are less likely to absorb moisture from the air and expand or contract.

You can also store the plywood in a climate-controlled environment to keep it from being exposed to drastic changes in temperature or humidity.

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.