How to Unwarp Wood: 3 Best Ways To Straighten Warped Wood

By MWB-Team •  Updated: 04/03/23 • 

Warping in wood results from uneven drying rates within the wood fibers. As the wood dries, one of the edges, end, or face of a piece of wood shrinks more than the opposite edge, end, or face, and the piece of wood warps.

Warping results from the wood’s shrinking and drying until it reaches an equilibrium with the relative humidity. This is also called equilibrium moisture content, or EMC. Apart from warping, wood can also absorb moisture and swell until it reaches the EMC with the surrounding.

Types of Wood Warping

Warping in wood can occur in several ways, all caused by directional shrinkage as it dries. Depending on the type of warping, you can learn how to fix the problem and restore the wood to good condition.

Types of wood warping

Types of wood warping

The four main types of warping are cup, bow, crook, and twist. One type of warping is not the same as another, and it will take your understanding of each to learn how you’ll fix and prevent it.

3 Ways To Straighten Warped Wood

Use an Iron

This is a simple method of fixing a warped piece of wood and works best if the piece of wood is thinner.

To start, cover the wood or affected area with damp pieces of towel. Once covered, place the wood on an ironing board or flat hard surface. Place the wood with the inwardly curved surface facing down for cupped and bow warping.

Once you properly wrap and position the wood correctly, turn your steam iron to its highest setting. Once it’s heated up, press it over the warped surface of the wood while applying pressure for around five seconds as you move it.

Keep checking on the condition of the wood and sprinkle more water if necessary until you’ve achieved a flattened shape.

Use Sunlight

This is the same method as using an iron, but instead, you’ll use sunlight to help straighten a warped piece of wood.

First, wrap the wood in moistened towels and place it on a hard surface outside in direct sunlight. The concave or bulge of the wood should face down to help fasten the process.

Once covered, leave the wood under direct sunlight and monitor the progress. Depending on the extent of the warping, the piece of wood can sit in direct sunlight for several days before it gets back to shape.

As the wood sits in direct sunlight, the sun rays heating the damp towels help the wood fibers absorb moisture. This helps the wood warp back into a straight shape. Keep checking on the towels to make sure they don’t dry out. Use a water sprayer to keep them damp while still monitoring the results.

Use Pressure/Weights

Using pressure or weights is another method of forcing a piece of warped wood back to its original shape. This is a good method for bow and twist warping, but it can also work for other types of warped wood.

First, cover the wood with damp paper towels or a thin cloth. The materials should cover the entire warped area. For a cupped wood plank, place the paper towel or cloth on the concave side to help it absorb moisture and bring it back into shape.

Once you’ve placed paper towels, wrap plastic around the affected part of the wood. The plastic wrapping allows only the affected part of the wood to absorb moisture.

After you’ve wrapped it properly, use two C clamps to secure the wood. Tighten it, but don’t overdo it, and keep checking on it. You can place it under direct sunlight or apply a heat lamp to the affected area for faster and better results.

Apart from applying pressure using C clamps, you can also use weights to straighten warped wood. Once you’ve wrapped the warped wood properly, lay it on a flat surface and place a flat weight on top of it. The weight will eventually push it down to the proper shape.

How to Prevent Wood Warping

Now that you’ve known some methods of fixing warped wood, you should also learn how to prevent the warping of wood in the first place. Different types of wood warping tend to be caused by different factors. Linking a type of warping to a problem will make it easier to prevent future warping. Below are some ways to prevent warping.

Properly Drying Wood

One of the main reasons why wood warps is how it is dried and cured.

Kiln drying is the best way to give your wood the best chance of warping. The process gives you or the manufacturer more control over how you dry the wood. Compared to the natural drying of wood, you’ll have more control over the speed and degree.

Kiln-drying wood helps it stabilize, thus making it harder to warp when exposed to changes in temperature and humidity. Another advantage of kiln-dried wood is that it is less likely to be damaged by insects or fungal activity.

Proper Storage Technique

The storage of wood also greatly impacts whether it will warp. Storing wood exposes it to moisture and other elements that might cause it to warp. Store wood in a clean and dry area to prevent wood fibers from absorbing excess moisture. Proper ventilation and airflow should also be observed in the storage area.

Apart from moisture and other elements, how you stack or arrange the wood is also important. Place your wood on a flat and level foundation and ensure an even distribution of weights on the wood.

Acclimate Before Installation

Before using wood, properly acclimate it to its new environment. Acclimating wood to its new environment exposes it to humidity and temperature, thus allowing the wood to adjust properly.

Acclimating can take between 24 hours and to 7-days. Once the wood acclimates, it makes it stable to work with, thus reducing the chances of warping.

Use a Sealant

Changes in the moisture content level of wood are the main reason for warping. To prevent the loss or gain of moisture by wood, you can paint, stain, or apply a protective sealant.

Using a wood sealer creates a protective barrier that prevents wood from absorbing water or losing moisture. This effectively prevents moisture, but depending on the type of wood sealer, you’ll have to redo it after several years.

Apart from helping to prevent warping, a wood sealer will also prevent the wood from staining and provide a protective barrier against daily wear and tear.

Use Stable Woods

Some woods are more likely to warp compared to other woods. You can use more stable woods that are less likely to warp to avoid warping. This is usually because the tighter grain or oils in the wood makes it less likely to absorb or release moisture.

Some stable wood you can use are Redwood, cedar, and fir.

Before using a type of wood, you can check if it is vulnerable to warping and if it’s suited for certain applications. Check out this wood handbook by the U.S. Department of Agriculture to learn more about different woods.

MWB-Team

Hello there! This is the Make Wood Better Team. Here, we share informative how-tos and guides focused on making wood better. Whether it's finishing wood, maintenance, or restoration, there's something on this website for you to learn and improve your skills.