December 10, 2022
Do you work with wood frequently? Are you in the lumber manufacturing business? Then knowing how to store lumber without it warping is a skill that will come in handy. Although wood generally tends to age well on its own, poor storage conditions can quickly destroy it. This may not only lead to the loss of quality in the lumber, but it can also affect your project and cost you lots of money.
There is a lot of wisdom to buying and storing lumber in bulk. For one, it means that you can get the wood you need at discounted rates. Also, you’d have extra lumber in wait for your next job. So, no more delays in projects due to the unavailability of wood. But this raises the million-dollar question – how do you store lumber without it warping?
However, you don’t have to look far to find the causes of warped wood. Indeed, one such reason is an excess amount of moisture in storage.
In this article, we have prepared a comprehensive guide on the best ways to store lumber without it warping. That is not all. You will also discover valuable insight into the causes of warping in wood. But first, let us start from the basics – what exactly is wood warping?
Facts About Wood Warping
Warping is a defect in timber products caused by uneven changes in the moisture contents of different parts of the lumber. In other terms, some areas of the lumber dry out faster than others. In other words, some areas of the wood dry faster than others. When this happens, one of the most obvious signs is bending or curving in some regions of the wood. Essentially, a warped piece of lumber will not remain straight or lay flat.
Warping in lumber occurs as a result of differential stress, which the uneven drying process causes. It may also happen when there is too much humidity where you store your wood. In this case, some areas of the lumber will experience an increase in their moisture content (%MC), which will also lead to warping.
Straight and unwarped lengths of wood are essential for making good furniture. If your boards are not straight and warped, they won’t be able to take the weight of the finished product. This means that you’ll spend more time planning and sanding them down. Furthermore, it also means you won’t need to spend money on warped and unsaleable lumber.
In essence, warping is a defect in lumber that is undesirable for many reasons. Now let us look at some of the reasons lumber in storage ends up warping.
Causes of Warping in Lumber
The first step to prevent warping in the lumber you have in storage is understanding why it happens. This way, you can relate to the various tips on preventing warping in lumber that we will share. In the next few paragraphs, we will break down the how and why of warping in timber products. So, you need to pay attention to.
One of the reasons why lumber warps after it goes through processing is that it has experienced a significant increase in its moisture content. Lumber is naturally hygroscopic. It will lose or absorb moisture for as long as it takes to achieve equilibrium with its surroundings.
So, if its surrounding is warm, wood will release moisture (dry out). When too much of this happens, the lumber may contract or crack. In other words, it warps. However, if the lumber’s immediate environment is wet or humid, the wood will absorb moisture from the air. Now, if this occurs excessively, the wood may swell to achieve an equilibrium with its environment.
Therefore, it is the drastic or excessive changes in moisture content that causes warping lumber. So, if you want to prevent warping in your store lumber, an effective strategy is to control the wood’s moisture content. But how do you do this? We will tell you in a few moments. But before that, let us show you the various types of warping that exist.
5 Types of Warping in Lumber
There are five types of warping in wood:
- Bow: Here the piece of lumber will stay flat across its face but bends upwards at the end. Looking at this type of warp from the side, it resembles a bow.
- Twist: Twisting warp causes the wood to turn inwards at both ends, thereby creating a twist.
- Kink: A kink occurs when the lumber bends upwards on one side. The resulting shape resembles an arm that is folding inward at the elbow.
- Crook: More often than not, this type of warp occurs when only one side of the lumber suffers excess moisture exposure. The crook resembles the letter C from a bird’s eye view.
- Cup: Finally, a cup is the result of the wood bending inward towards its middle. To get a clearer picture, think about the long edges of a piece of paper that you’ve rolled towards its center.
One point to note is that the various types of warping do not have a mutually exclusive relationship. In other words, one piece of lumber can experience multiple combinations of the types of wood warping. Then again, it may exhibit only one. That said, let us dive right into the various ways you can store lumber without subjecting it to warping.
Techniques & Methods of Store Lumbar And Prevent Warping
Now that you understand what warping is and why it occurs in lumber, let us show you how to prevent it. In the next few paragraphs, we will give you pro tips on storing your lumber while ensuring it does not warp. Here’s how to keep your lumber the right way.
1) Always Use Clean & Dry Storage
It may be impossible to overemphasize how important this point is. You see, where you store your lumber has the most significant effect on its moisture content and subsequent changes. Therefore, if you want to give your stored wood the best chances of retaining its quality, we recommend clean and dry storage.
However, if you cannot ascertain that the area will stay dry, don’t panic yet. There is a solution. You can wrap your lumber in a material that is vapor-resistance. This is especially important if your storage area has a relative humidity of 80% or more. By wrap-proofing the lumber, you prevent it from absorbing excess moisture from its surrounding.
2) Store Unseasoned Wood Outside
If you want to air-dry your lumber, it is best to do it outside. Otherwise, you may negatively affect the quality of the other dried timber. You are probably wondering how, and rightly so. The reason is simple. Moisture from the drying and unseasoned wood will escape into the air and influence the storage area’s humidity.
When this happens, it is all too possible that the dried wood absorbs this moisture, which may cause them to warp. Moreover, air-drying indoors will only extend how long the drying process for the lumber takes. So, it is a win-win to dry unseasoned wood outdoors.
3) Store Kiln-dried Lumber Indoor
For storing kiln-dried timber, we recommend keeping this type of lumber indoors as much as possible. Generally, the moisture content of most indoor storage areas is usually lower than the levels outside. Furthermore, there is typically less humidity. These are the exact conditions that promote the longevity of kiln-dried lumber.
If you don’t have a lumber warehouse, you can use your workshop. Your garage or other covered storage units will also do the trick. The goal is to keep the moisture content to the barest minimum to prevent warping in the wood.
4) Pile Lumber on Flat Foundation
The best way to store lumber is to keep it in a horizontal stack if you have space. This will ensure that moisture does not move from one end of the wood to the other. But here’s a point to note. While stacking horizontally, ensure that you place support brackets between every 16 inches of wood. Doing this at a consistent interval will prevent the planks from bending into a bow.
However, if you need to save space and cannot afford horizontal stacking, you may store your wood vertically. But there’s a catch. The wood must be completely dry. It is also advisable to support the wood at the top and bottom to keep it from bowing. Finally, while storing wood vertically, the best practice is to keep it off the ground to reduce the chances of water damage.
5) Don’t Overstack Lumber In One Pile
While creating a horizontal stack of lumber on a shelf, you need to be wary of stacking too much lumber in one pile. Otherwise, you may prevent your lumber from being able to breathe, which may cause warping. Moreover, arranging too much wood on top of one another will place excess weight on the bottom. This can compromise the quality and integrity of the bottom one. Therefore, take good care not to stack too much lumber in one horizontal pile. This brings us to our next point.
6) Sticker Your Lumber
If you’re new to the woodwork scene, you’re probably wondering what stickering is. Stickering is a method of creating horizontal stacks of lumber in which you support all your boards with 1-inch scrap woods. This ensures that your limber has some space to air-dry and, most importantly, prevents it from warping.
Stickering is especially essential for lumber that comes from a sawmill. But you may apply the knowledge to any wood stack. By stickering your lumber, you ensure that it stays flat and supported. Furthermore, it ensures that the lumber stays in a state of uniform moisture content for as long as possible.
7) Monitor The Moisture Content (%MC)
Another essential tip to prevent your lumber from warping in storage is to keep track of the humidity levels in the storage area. Also, you will need to take readings of the moisture content in the wood itself. Most large factories with large timber stocks in storage use hygrometers to keep track of their moisture contents. You can apply the same devices in your storage too to stay ahead of the moisture.
However, you must note that all thermo-hygrometers have an error margin (sensor tolerance). This number usually revolves around +/-2% of the indicated humidity level and the actual one. Therefore, if you’re measuring RH (humidity) levels in an area, it is more effective to take multiple readings. Then, you find the average.
And, you can use a moisture meter to measure the moisture level of the lumber. Knowing both moisture content in your storage and lumber will prepare better and prevent warping.
8) Cure Your Stored Lumber Properly
Finally, if you’re curing your lumber yourself, how well you do can make the difference between warped wood or not. By curing your timber until it is completely dry before you store it, you increase its resistance to warping. Here are some tips to ensure that your curing process is very effective:
- Do not dry your lumber too slowly as this may allow moisture to remain long enough to wreak warping havoc.
- Do not overdry your lumber as this may induce cracking.
- It is best not to expose curing lumber to humid conditions. Otherwise, your wood may not be able to lose as much as it should.
- Drying and warping happen faster at the end of wood pieces. So, you may choose to seal those areas of the lumber to prevent warping. According to Guidelines on Storage of Lumber from U.S. Department of Agriculture Forest Service
- use Anchorseal to seal the ends of the stored green boards, as it will slow down the drying process and also make the drying process of all lumber sections more even. Slower dying will minimize the risks of wood warping and defects.
- Do not stack too much wood on one shelf as excess weight is never good for wood.
- Always ensure that your stored lumber has some space to breathe.
- When measuring moisture content in your storage area, do not test in areas with restricted airflow (corners).
- Instead, carry out RH testing in areas that are a good representation of the storage area’s general atmosphere.
- Place heavy weights on piles of lumber to prevent it from cupping.
Frequently Asked Questions About Storing Lumber to Prevent Warping
Aside from knowing the different tips on how to prevent warping of wood, it will also help if you are familiar with the various FAQs about how to prevent warping of stored lumber, for they might also be the questions you have in mind:
Why Should You Use Dry Wood?
Wood usually shrinks and alters its shape when it dries. So, most woodworkers want to ensure that their wood has already dried and reached its maximum shrinkage. Freshly cut timber is usually heavy or twice as heavy as its weight when dry. Besides, wet wood is usually more susceptible to rot or decay if you leave it untreated.
However, some woodworkers tag themselves as green woodworkers. They use fresh wood in their woodworking activities and when building furniture. The furniture they make is rustic in characteristics.
How Can You Determine If the Wood is Completely Dry & Suitable for Making Woodworking Products?
One best way to know if the wood has already dried entirely is by using a moisture meter. Moisture meters come in two types: pin-style meters and pin-less meters. Pin-style meters come with pins you can insert onto the wood to measure its electrical resistance. The measurement you get is usually indicated as moisture percentage.
Pin-less meters, on the other hand, utilize radio frequencies to get the moisture levels. They are also more expensive. Nevertheless, they don’t leave behind pinholes in the wood.
They also provide more precise readings, especially in a dense wood, where pin-style meters have difficulty penetrating. The prices of these moisture meters range from $50 to $200.
Can I Use Quartersawn Boards Instead of Flatsawn Panels as Tabletop?
Yes, you can use quartersawn boards for your tabletop. Besides, the quartersawn boards are less likely to contract and expand across their width. Moreover, they are not prone to cupping.
How Much Can a Wood Contract and Expand?
Kiln-dried wood will likely expand in width from 1/8″ to 1/4″ for every foot. This change might not be that much, but it can be problematic when this wood expansion and contraction add up.
Does Wood Dry Up in Stages?
Yes, the wood dries out in stages. The first stage is when you cut a tree and reduce its trunk into manageable sizes, the saps are still there, and the wood remains the same in size. Then, if the moisture gets extracted over time, the wood starts shrinking. This stage brings the moisture content of the wood down by 30%.
The next stage is the stage wherein moisture leaves the walls of the cells of the wood. You’ll see a noticeable difference in the size of the wood when this stage happens. The wood begins to shrink, and it becomes harder and denser. Besides, it becomes stronger.
How Much Time Does It Take for the Wood to Thoroughly Dry and Stop Shrinking or Expanding?
Wood will never stop changing its dimensions. Besides, it tends to reach equilibrium (EMC) regarding moisture content. But when it reaches EMC, the point where it no longer absorbs or gives off moisture, it reaches its most stable point.
The EMC of boards usually changes depending on their relative humidity changes. To avoid this change, you need to keep the boards in a controlled environment wherein humidity and temperature are kept from fluctuating.
Does Wood Equally Shrink or Expand in All Directions?
The answer to this question is a big “No.” Besides, the shrinkage amount differs from one species to another. On average, wood shrinks by 8% to 10% tangentially and 4% to 5% radially. It also almost does not shrinks lengthwise.
So, if you look at the rate it shrinks, you will see that the board’s point where the grain intersects the surface perpendicularly is the point with the maximum shrinkage. This indicates that wood of varying sizes will tend to shrink differently, depending on how the wood has been cut.
Hopefully, we have given you insight into how to store your lumber while preventing warping. Remember, wood is a natural resource subject to influence by many conditions, including the weather. But, by putting the right measures in place, you can extend the wood’s longevity and preserve its quality.
Do you have further questions? Perhaps, you’re looking to secure high-quality lumber. Please reach out to us.
Jason is a 40-year-old woodworker, carpenter and author who have been involved in the woodworking and woodcraft industry with 17 years of experience. He is expertise in technical aspects, woodcraft and furniture building projects.