Photo: Felicity Tai

Will plywood warp if left outside?

Plywood is manufactured from thin wood veneer sheets; the sheets are laminated and glued together. It can warp very easily if not stored or handled properly.

abutterflyhouse.com - Tested! 3 Ways to Save Warped Plywood - A Butterfly House

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Have you ever kept plywood stored in a garage waiting to be used on that perfect project only to find that it has warped when you go to use it? Before you decide to dispose of the warped plywood, let’s find out if there are any ways to save warped plywood. You can save warped plywood by spraying the bowed area with warm water and laying it down on a flat warm surface, humped side up, wet side down. Once the plywood is flat, place it in a cooler spot to cool down, then store it in a dry location for use later. Plywood is manufactured from thin wood veneer sheets; the sheets are laminated and glued together. It can warp very easily if not stored or handled properly. Let’s delve deeper to find out what can be done to save warped plywood and find out some of the reasons plywood warps. This blog contains affiliate links. If you click and make a purchase, I may receive compensation (at no additional cost to you.)

Why Plywood Warps

Lets do a quick explanation of why plywood warps, so you have some idea which ideas are junk, and which are actually good. Plywood warps because the layers of wood soak up different amounts of moisture from the atmosphere. This causes the side that soaked up more moisture to be slightly larger than the other, causing warp. The convex side of the plywood soaked up more moisture, while the concave, “cupped” side soaked up less. While the first method of saving plywood just attempts to flatten with force, some of the other methods try to even out the moisture discrepency.

How Can Warped Plywood Be Saved?

There are various ways to save warped plywood and ensure that they are in shape to be used again. The best way to save the warped plywood would be to flatten it. I have listed a few options below; you can decide which one would work best for you.

Place The Warped Plywood In Direct Sunlight

Warped plywood is easy to straighten out with a little help from the sun! Spray a generous amount of hot water onto the concave area of the warped plywood. The concave area refers to the interior of the hump that has been formed due to the warping. The plywood sheet can be set on a flat surface, preferably a driveway that receives adequate exposure to sunlight. When placing the plywood sheet, ensure that the humped side faces upward and the side that has been sprayed with water faces down. A heavy object can be positioned on top of the hump of the plywood to help it flatten out. The plywood should be left in the sun for as long as it takes to start showing signs of flattening. It is advisable to check on the progress every five to 10 minutes to avoid overexposure to the sun. As soon as it is flat, place the plywood indoors in a cooler spot. This method applies moisture to the shorter side of the plywood, swelling it a bit, while applying sun to the other side to remove moisture and shrink it.

Theoretically, this should help un-warp the plywood. I gave it a try.

I did this inside because I live in Minnesota, and temperature matters. The warmer your spot, the better for this. Inside, in front of large window that gets plenty of morning sun was my best bet. It definitely made a difference, and my plywood was less warped afterward. It wasn’t perfect, but the bit of warp that was left could be easily flatted with the next method.

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Use A Heavy Weight To Flatten Warped Plywood

This technique is probably one of the easiest to follow, with just a few easy steps;

Lay the plywood on a flat surface

Place heavy weights evenly across the panel without bending the edge of the plywood. Dumbbells generally work the best. Leave to stand overnight and notice the difference in the morning. If it has not reached the full desired effect, you can repeat this process daily until the warped plywood is completely flattened. Note that the heavier your objects, the better. Also, don’t be alarmed if you have to repeat this process for multiple nights. If you can leave it for a week, that’ll make a bigger difference. A lot of the time, if I bring home a piece of plywood that’s warped, I’ll just put it on the bottom of the stack. That way, the other pieces of plywood will weight it down and slowly flatten it, and then by the time I need it, it’s ready to go. This is why when you go to the home improvement store, you’ll often see that the pieces at the bottom of the stack of plywood are nice and flat. At the moment, my plywood flattening pile is a catch-all for scraps and other wood I hope to use soon, but I’m on a new workbench that will have space at the bottom for medium-sized pieces of plywood to sit and flatten.

Coming soon!

Using Clamps to Remove Warp From Plywood

This method works the same way as the heavy weight method, however it can be used even if you don’t have anything heavy to work with!

Lay the plywood on a flat surface

Clamp the plywood to the flat surface in multiple places, flattening the board If your clamps can’t reach part of the plywood, place a paint can or other heavy object on top of that section Leave to stand overnight and notice the difference in the morning. If it has not reached the full desired effect, you can repeat this process daily until the warped plywood is completely flattened.

A Method That (Predictably) Didn’t Work

If you have a steam iron, the internet told me that can work to flatten warped plywood. It goes something like this: Place the board on the ground, and put a damp rag on top of it. Carefully press down on the wood to flatten it, using the hot steam iron to apply pressure. Since it’s a steam iron, you could use that feature as well, but the heat from the iron on the damp towel will create steam too. Keep moving, and never apply the iron for longer than 30 seconds in one spot. You don’t want to cause a fire. Once you have flattened the warped board, place weight on it and leave it overnight so that it doesn’t re-warp. The problem with this method is that you’re applying both heat and moisture to one side of the board, where to flatten plywood, you want to apply heat to the longer side, and moisture to the shorter side. Additionally, it’s much easier to flatten the board if you’re sitting on the convex side applying pressure. But the best place to apply the heat and steam would be the concave side, which is the side that needs to absorb the moisture. So, I had no luck, but admittedly I was probably applying steam to the wrong side. So if you try this, apply the steam to the concave side, and let me know how it goes!

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Saving Plywood That Has Been Warped By Rain

If your plywood has been exposed to rain, there is still some hope of saving it. In areas with dark discoloring, where the moisture has started to soak in, you will have to keep the plywood covered and remove as much moisture as possible by drying out the plywood.

You can dry out the warped plywood by:

Storing the plywood indoors.

Remove excess water by covering the board with cloths or sawdust to help draw out excess moisture.

Use a high-powered fan to help dry out the moisture quickly.

Warm up the room temperature by using a heater.

Leave the plywood to dry for a couple of days.

How to Prevent Plywood From Warping

Plywood is likely to warp regardless, but there are a couple of things you can do to minimize the possibility.

Store the Plywood Properly

Incorrect storage of plywood can cause it to become warped over time. Warped plywood is largely due to moisture and temperature changes. The shrinking of the plywood causes warping. You can alleviate this by storing the plywood in a room around 35 degrees Celsius. You can also seal your plywood with a water-resistant sealant spray. Ensure that you coat both plywood faces with the same coating system to avoid moisture differences. The result of moisture differences can lead to warping. It also helps to store your plywood horizontal and flat, not vertically against a wall. If you’re working in small shop, this can be difficult to do, but if you can find a spot that isn’t taking up extra square footage, do it.

Keep Plywood Flat and Dry During Transport

Although plywood is easy to transport, it can quickly warp if not transported properly. When too much pressure is put on the plywood during loading, it can cause it to warp, especially if one side is getting pushed down and another side lifted. The pressure causes tension on the plywood, which causes it to buckle into a concave shape. If the plywood has not been transported in a flat position, the plywood will tend to warp when unloaded. If you are tying up the boards with straps, make sure not to tighten them too much around the boards. Tight straps can cause dents and warp due to uneven distribution of weight. To avoid this, you can place the boards flat and strap them down securely (but not too tight!) with tape or straps. The tape will help restrict the movement of the boards when transported. If you have no other option but to load into a smaller vehicle, it would be best to lay down old sheets of plywood first so that your newer plywood can rest on a flat surface. Then load each piece separately with their best side facing downwards.

abutterflyhouse.com - Tested! 3 Ways to Save Warped Plywood - A Butterfly House

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