The success of wood projects sometimes depends heavily on the quality of the wood used. Unfortunately, wood can get warped, making it challenging to create a successful project without fixing the warped lumber.
You do not have to lose the wood if you know how to straighten warped lumber.
Read along to learn how to unwarp wood in six tried and tested methods. The article also discusses the common causes of wood warping and provides useful tips for preventing the wood from getting warped.
What is Wood Warping?
Wood warping is an undesirable change in the shape of lumber occasioned by uneven changes in the moisture content in different parts of the piece of wood.
Warping can occur on an entire wood board, the sides, or the edges, resulting in different types of wood warping.
How to Unwarp Wood: At a Glance
To unwarp wood, make the wood moist by covering it with towels soaked in water. Next, wrap the covered wood in nylon paper and apply pressure on the warped side by placing bricks or a similarly heavy object on the warped side or section of the wood.
The moisture will make the wood pliable while the pressure forces it back to its original shape.
What Causes Wood to Warp?
When you buy wood, it has often achieved its equilibrium moisture content, or EMC, where the wood is not gaining or losing any more of its moisture.
Still, some factors affect this state of balance, leading to further loss or gain of moisture, leading to warping. Here are some of the culprits likely to cause wood warping.
Prolonged exposure to moisture and humidity
One of the most notorious causes of wood warping is humidity. Untreated wood has open pores on its surface. If you keep such wood in damp environments or places with high atmospheric water vapor levels, it will suck it up.
If this exposure to dampness or humidity goes on for long, the sides of the wood directly exposed to moisture will become distended, leading to a crooked shape.
Ideally, wood should increase in shape and shrink when it absorbs and loses moisture, respectively. Unfortunately, this process never happens uniformly due to the non-uniform exposure to the elements and the varying density of different parts of lumber.
Prolonged exposure to heat
Wood typically retains some moisture content even when it is dry. However, when subjected to direct sunlight or heat for too long, the heat occasions accelerated moisture evaporation from the side exposed to the heat.
As a result, the exposed side will shrink faster than the side facing away from the heat source, leading to crookedness.
Ants, beetles, and other boring insects can damage and destroy lumber by consuming it and creating holes in it.
This attack loosens the wood’s fibers, causing it to kink, bend or warp under its own weight. Insect attacks can also leave the damaged side exposed to water and moisture, resulting in warping.
To properly store timber in a woodshop, it is important to use flat surfaces that can support the weight of the wood without bending. This is where timber storage racks for woodshops come in handy, as they provide the necessary support for the timber.
Storing the wood upright or without proper support can cause the timber to bend over time, resulting in warping.
In addition to using lumber racks for woodshop, it is also crucial to ensure that the wood is fully dry before storage. Storing wet timber for long periods is not recommended, as the moisture can cause the wood to warp over time.
Therefore, it is best to let the wood dry completely before storing it on the racks. Read our article to answer your question “How long does it take wet wood to dry?”
By taking these precautions, woodworkers can ensure that their timber remains in good condition and ready for use in their projects.
How to Fix Warped Wood (6 Methods)
While warped wood can be highly undesirable, you can reverse the problem by following a few tricks to flatten warped boards.
Method 1: Using an iron
The first warped wood fix involves using a hot iron box. To complete this process, you will need the following supplies:
- An iron box
- One or two towels
- Water source
- Power source
- Ironing board or any flat, sturdy surface
Procedure for fixing warped wood using an iron
- Start by wrapping the warped wood with thick towels dampened with water. You want to make sure the damp towels cover every inch of the warped section of the wood you want to fix.
- After wrapping the wood, place it on an ironing board or other flat, sturdy surface that the wood cannot damage. Ensure the curved side of the warped wood is facing up.
- Turn on your iron and set it to the highest heating point. Ensure you are using a steam iron for the best results.
- Once the iron is hot, press it against the warped wood surface, keeping the pressure gentle and even as you move it all the way over the affected surface.
- Stop from moment to moment to check the progress until the warping is gone. This method may take time to fix the warping, so consider being patient. Additionally, the iron method is more suitable for thinner wood boards.
Method 2: Using pressure from clamping
The clamping method is ideal for thicker, longer boards that require more force to fix. This method requires covering the concave side of the warped wood with damp paper towels or a thin steaming towel dampened with water.
You want to ensure the material is damp and not dripping when draping around the affected wood. This technique concentrates moisture on the hollow side of the wood, moistening it and causing it to swell back.
The increase in size on one side should help reverse the warping with the help of the wood clamp.
Here is the list of things to use in this procedure.
- Damp paper towels or steaming towel
- A clamp
- Plastic wrap
Procedure to follow
- Begin by stashing damp paper towels on the hollow side of the warped wood, covering it completely. You could also use a thin steaming towel in place of paper towels for this purpose.
- Apply several layers of plastic wrap over the wood, locking in the sheets of paper towels tightly and securely. Wrapping the plastic around the wood with moist paper towels helps secure them onto the wood and slow down evaporation.
- Finally, place the wood in a clamp and tighten the tool over the warped area. Once the warping begins to straighten out under pressure, leave the setup clamped for about a week.
- Check the setup regularly to assess the progress. If you notice damage such as the wood cracking, undo the clamp and use a different method. Otherwise, keep it clamped until the warping is fixed.
Method 3: Drying in the sun
The sun method uses the power of moisture and the heat from the sun to fix and straighten the warped wood. The wood first absorbs moisture from the towels and becomes malleable.
Since the convex/swollen side of the wood faces the sun, it dries faster than the side facing away from the sun. The resulting shrinkage on this side should force the wood back to its straight shape.
What you will need to unwarp wood through this method include:
- Large towels dampened with water
- Access to adequate sunlight
- Water sprayer
- Plastic sheeting or tarp
- Rigid surface
Steps to follow to straighten warped wood
- Dampen a few large towels, rags, or sheets with water and wrap them around the warped plank, covering it completely.
- After covering the wood in damp towels, set it out in a warm outdoor area with access to direct sunlight, keeping the concave side facing down (away from the sun). You could place the wrapped plank on a bench, the deck, or any flat, rigid surface that receives a lot of sunlight.
- Keep the wood in the sun for two to four days, depending on how much warping you want to straighten.
- Keep spraying the wrapped wood from time to time to keep the towels moist throughout.
- After the recommended number of days, unwarp the wood and check if it has been straightened. If not, consider using a different method.
Method 4: Using nylon paper, a damp towel, and some bricks
This technique closely resembles the clamping method, but here you use bricks or some equivalently flat, heavy objects instead of a clamp to apply pressure.
Like in the clamping technique, the principle here is to make the wood pliable using a damp towel and then exert force on the curved side using the bricks.
Here is the list of things you will require.
- Bricks or another similarly heavy object
- Damp towels
- Nylon paper
Procedure for unwarping the wood
- Begin by wrapping the wooden board in a damp towel, entirely covering the warped section.
- Wrap the warped lumber now covered in a damp towel in nylon paper.
- Place the bound plank on a rigid surface with the convex side facing up. Next, place some bricks or a similar heavy object on the warped section of the lumber.
- Leave it there for a few days and check to see if the warping is fixed. The weight of the bricks should help flatten the deformity.
Method 5: Using heat and steam to straighten bow warps
While sunlight is a slow way of heating an object, you can swap it with another source of heat, such as a heat lamp, when dealing with bow warping. In this case, you will forgo the towels and spray water directly on the wood once it is heated.
Once the wood has absorbed enough moisture, making it bendy, you can manually straighten it back.
The tools and materials you will need include:
- Flat surface
- Water spray
Steps to follow
- Start by slightly heating the wood for ten to twenty minutes and then spray some water on it. The heated wood should easily absorb the moisture you introduce, making it flexible.
- After curving the wood with water, straighten it by applying physical force and tying it to a flat surface or clamping it on both ends with the curvature facing up.
- Leave it attached to the flat surface for some time to dry, and then check to see if the wood warp is gone.
Method 6: Using a jack plane to fix cup warping
If your lumber has slight cupping on its surface, you can use a jack plane to undo that imperfection. Using a jack plane is a quick and effective warped wood fix, but the cupping must be only slight for it to work.
The tools and supplies you will need here include:
- Jack plane
- A hardwood workbench
- Drop cloth
Procedure for straightening warped wood
- Use a spirit level or winding stick to check for cupping on your wood. When doing this, you must lay the board on a flat surface, preferably a workbench. Use a pencil to mark the cupped areas.
- Turn the wood and check for bowing (curvature on the opposite side of the board).
- Lay a tarp on the floor or ground beneath your workbench to collect the wood debris. (Also find out the ideal workbench height to ensure comfortable working conditions)
- Plane the wood depending on the deformity—plane across the width where the center of the wood has dropped, and the edges are raised. Next, turn the plank and plane down through the center on the raised side to flatten it across the entire length.
Types of Wood Warping
Not all wood warping is the same. This section discusses the different ways wood can warp.
This warping is characterized by a sudden bend at an angle along the length of a slat. The problem is common with softwoods with grain distortions or knots.
This is a case where the board is curved lengthwise, often due to the top side of the board laid on a flat surface drying faster than the bottom facing side.
The accelerated drying process on the top-facing side results in its shrinking, causing the board to form the shape of an archer’s bow.
As the name suggests, this warping is characterized by twisting of the wood plank somewhere along its length. A spiral or diagonal grain is often responsible for this type of warping.
This warping is when a wood board is carved along the entire length of its edge instead of its side (as in the case of bow warping). This is among the least common forms of warping.
Cup warping is when a fairly wide-faced piece of lumber drops in the center over its width to form a convex or U shape from one end to the other—hence the cup.
How to Check for Warps, Bends, and Twists in the Wood
Substantial wood warping will stick out and be noticeable when you eyeball the affected piece. However, minor wood warps may not be as obvious, and you may need to know how to check for warps, bends, and twists to detect them.
Here is some help.
Option 1: Lay down the wood on a flat, level surface and visually inspect it along its entire length. You should see the crooked parts if the piece is warped.
Option 2: Hold the plank with one end to your eye and the other to the ground, and visually inspect it all way around along its entire length.
Option 3: Use a winding stick to check for any warped parts on the timber. Start by laying the wood on a flat surface and then inspect it with the help of a winding stick, running the equipment down the length of the board.
How to Prevent Wood Warping
Straightening warped pieces of wood will help you save on the cost of replacing the affected piece. However, the process may involve some elbow grease and can be time-consuming. The best workaround is to prevent the warping from occurring in the first place.
- Treat the wood to make the wood moisture-proof. Sealing the wood with protective sealants like polyurethane, oil-based paints, or epoxy sealants should block the pores and prevent moisture from entering it, maintaining its structure.
- Store wood properly. Providing the wood with the right support on a flat surface away from dampness should help prevent it from warping. Here is more on how to prevent wood from warping outside.
- Do not dry the wood beyond the recommended limits. You can use a piece of equipment such as a wood moisture meter to monitor the moisture content of your lumber.
Can you fix a warped piece of wood?
Yes. You can fix warped wood with a method as simple as using a household iron to apply heat and pressure to the wood after wrapping it in damp towels. It may take some time to straighten warped wood if it is thick, so be patient.
How to straighten a warped board
Wrap the warped wood in moistened towels and iron it over the warped surface with the iron set to its highest heat setting until the wood straightens.
How to straighten warped 2×4
Cover the hollow part of the warped 2×4 plank with damp paper towels, bind it with plastic wrap, and clamp it with the concave side facing up.
Can you fix wood warped by water?
Absolutely. Applying additional moisture to the opposite side of the warped side and heating it can help correct the wood warp, fixing the problem. If you go overboard when using water, you can quickly check how to fix water-damaged wood table top.
How to flatten wood planks
To flatten warped wood planks, simply change the moisture content on one side of the affected board. Begin by identifying the cupped or concave side of the affected plank and then spray water on it to relieve the tension and allow the shrunk fibers to expand, allowing the board to flatten.
Recommended read: Does wood swell in heat or cold?
Final Thoughts on How to Unwarp Wood
Several methods can effectively help fix a warped piece of wood. However, not all methods of unwarping wood will be effective against all types of wood warps.
So, if one method does not unwarp your wood board, try another one. Better still, practice the tips and tricks we have provided in this guide to help prevent your wood from getting warped in the first place.
Did we cover everything? Leave a comment to let us know your thoughts about fixing warped wood.