How To Straighten Warped Wood

(Last Updated On: March 22, 2021)
Workers checking the warped wood board.

Wood usually warps as a result of stress, uneven shrinkage, or drying. Sunlight, uneven finish, or airflow may also be a factor in wood warping. Moreover, grain orientation, temperature, or wood species may be a contributing factor as well. Using warped planks, however, is difficult and problematic, especially if you are framing a home or using them for the subfloor. Hence, you need to straighten the warped wood before using them. 

Methods for Straightening Warped Wood

There are several types of wood warping. Wood warping can be bow, crook, kink, cup, or twist. There are also several methods that you can follow to fix warped wood. These methods may use winding sticks, pressure, heat, or sunlight to bring back the wood to its original flat shape. Below are the four primary methods that you can try to fix warped wood:

1) The Use of Winding Sticks

The use of winding sticks is a good way to determine if a wood is warped. A winding stick is a stable wood like mahogany that you can use to determine the extent of the warping of another wood. To use the winding sticks, you simply must place the wood on any flat surface. Then, determine the warp’s type using your winding sticks. If the wood is twisted, you can use a plane to rectify the warping. You can plane the wood diagonally along the wood’s high line. 

You can also use a single winding stick to determine if the wood is bowed. You can do this by simply dragging the winding stick along the surface of the wood. If you notice that there’s a space or gap in-between the wood and the stick, then the wood is bowed. You can rectify bowed warping by making cuts on each edge of the higher sections of the wood to remove these high sections. You should do this across the length of the wood. 

If the warping is prominent in the middle section, you can make cuts on this part of the wood. Then, check again for warping and ensure that the warps are corrected. 

2) Use Sunlight to Correct the Warp!

Woods are reactive to moisture. So, if you want to reverse the process of warping, you can also use moisture to unwarp wood. However, you will need sunlight and several wet towels to unwarp the wood. Here’s how you do it:

  • Soak in water the towels and wring off excess water. 
  • Wrap the warped wood with moist towels.
  • Position the warped wood on any flat surface like a deck or soft surface. 
  • Place the wood directly under sunlight with the bent section (convex part) inwards facing down.
  • Spray water on the parts that have the wrapped towels. 
  • Keep the wood in sunlight for 2 to 4 days. 
  • During the nighttime, keep the wood in a warm room. 
  • Constantly spray water on the wrapped towels for the duration of this period. 
  • Regularly check on the wood to see the progress of the unwarping process. 
  • If the warping has been corrected, you should remove the towels and dry the wood. 
  • If warping is not rectified, then you need to make use of another method. 

3) Use Flat Iron

You can also use heat to rectify the warping of the wood. You can do this by using a flat iron to heat up the surface of the wood. You would need two large moist towels to achieve the unwarping process. 

  • Thoroughly drench the towels and then wring out the excess water. The towel should not be wet but only damp. 
  • Position the warped wood on a flat surface. Choose a surface that can withstand high temperatures. Make sure that the concave surface is facing downwards.
  • Wrap the towels around the warped part of the wood.
  • Set to the highest settings the iron box. Allow it to heat up for several minutes. The best iron to use for this purpose is a steam iron. 
  • Once the iron is heated, you can press the iron on the wood’s warped surface. Apply even pressure as you slide the iron across the surface of the wood. Keep the iron box for at least 10 seconds in each position. Don’t leave the flat iron unattended to avoid damage to the wood. 
  • Inspect the warped surface if it has been rectified. If the warping has stopped, you can stop the process and dry the wood. If the warp did not stop, then, try another method. 

4) Apply Pressure

You can also apply pressure to rectify the warped surface of the wood. You will be needing moist towels likewise, as well as clamps to apply pressure to the warped surface. You can do this by following these steps:

  • Cover the warped surface with moist towels with the curved section facing inwardly. You can use paper towels for this purpose. These paper towels should be wide enough to cover the warped surface of the wood. 
  • Once you’ve covered the warped surface with moist towels, wrap the paper towels with plastic. Make sure that you tightly and securely wrap the moist towels with plastic. You should do this to minimize evaporation and keep the surface of the wood moist. 
  • Clamp the wood. Tighten the clamp till the warped part straightens. Be very careful not to overtighten, or the wood may split. 
  • Keep the clamp on the wood for a week while you observe the shape of the wood regularly. Make sure that you store the clamped wood in a room with a temperature of around 77°F or 25°C. Do not store the clamped wood in a very humid room. 
  • After a week, you can remove the plastic wrap and paper towels. Ease the wood from the clamp. If the warped had been rectified, you can then dry the wood and use it afterward. If the warped is not yet fully corrected, you can then repeat the process and apply more pressure to the warped surface. If this method does not rectify the wood, then, it is time to conclude that the damage to the wood is irreversible. 

Why Does Wood Warp?

Woods differ in quality. Some woods have a denser grain structure. Some., however, have a fine grain, while some have very knotty grain. Some woods are shock-resistant, while others are not. Depending on the quality of the wood, each wood has its tendency to warp when exposed to different outside factors. 

As mentioned above, wood may bow, crook, kink, cup, twist, or wind. A bow is a type of warp along the wood’s length. Crook, on the other hand, is a warp along the length of the wood’s edge. Kink, however, is a localized crook that is caused by a knot. Cup is a warp across the width of the wood’s face, while twist or wind is a distortion wherein the two ends are not aligned.

Wood warping costs homeowners and even the wood industry millions of dollars annually. Sometimes, straight wood boards get transported from the cutting facility only to arrive at the store yards already warped. 

Although a lot of studies have been made to prevent wood warping, the warping control model hasn’t been updated for several decades. At present, there are studies on how to prevent wood warping. These studies hope to rectify the manufacturing process. These studies also aim to provide manufacturers with much information on how to prevent wood warping.

Studies on Improving the Resiliency of Wood against Warping

Dr. Zhiyong Cai, of the Texas Agricultural Experiment Station, for example, has been involved in research about wood warping. His study examines new techniques on how to understand warping. He said that understanding warping is crucial to preventing warping. His study is designed to provide manufacturers with good tools to help them make the right decisions in wood manufacturing. 

According to Cai, the present warping control model for wood composite manufacturing is a one-dimensional model. However, wood composite panels are two-dimensional because woods are multilayered products. Each layer, therefore, has its own behavior. Then, uses commercial spreadsheet software along with a complicated formula, to come up with the conclusion that wood panels have 10 layers with different properties and orientation. 

With this 10-layered model of composite wood panels, manufacturers can figure out the linear expansion of any wood-based panel. They can also make the necessary adjustments in their manufacturing process. Cai also said that he intends to produce a computer model that manufacturers can use. In this way, his theory will be made applicable in the actual setting. 

Conclusion

Warping is a problem that may be costly to manufacturers and users of wood. Rectifying it may be laborious and entails hard work. Preventing the warping of wood may be easier than engaging in the unwarping process. Hence, it is better to know the factors that can cause wood warping to prevent it. Moreover, if you don’t want to engage in unwarping wood, you better choose woods that resist warping. Some wood species like those of redwood, cedar, and fir are less likely to warp or crack than other types of wood. 

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