Plywood is a versatile and cheap wood material. While it has some limitations, plywood is an indispensable choice for many woodworkers. If sealed and handled properly, plywood can last long and endure harsh elements. However, many of our readers ask: does plywood warp?
Unfortunately, plywood is prone to warping. It’s not surprising for a pressure-treated wood material like this. In this post, I will discuss what is warping in plywood and what you can do about it.
Why does plywood warp?
Plywood warping can be due to a lot of things. The most common culprits are excessive moisture and heat.
When plywood is exposed to high levels of humidity, the moisture in the air will be absorbed by the grains. Over time, this will cause the plywood to swell and warp. If the plywood is alternately exposed to heat and moisture, it will start to lose its form.
Moreover, if only one side of the plywood is covered from harsh elements, it will warp just the same. Therefore, it’s much better to cover your plywoods on both sides to prevent moisture from getting into the grains.
The concave side of warped plywood often contains lesser amounts of moisture compared to its concave side.
How to flatten warped plywood
The good news is that there’s a way to flatten warped plywood. As long as the wood material isn’t crumbling or rotting, you can still refurbish it with a few steps. Here’s what you need to do:
Step 1. Spray hot water on it
The first thing you need to do is spray hot water into the concave part of the plywood. This is the interior hump, which contains less moisture.
Step 2. Set it on a flat surface
After applying hot water, you need to put the warped plywood on a flat surface. The area should have proper ventilation and warm air. Your driveway on a sunny day is the perfect spot for this purpose.
You should also place the convex side (exterior hump) face up, so the side you put hot water on is facing down.
With this in place, put heavy objects on top of it so the warped plywood would flatten back to shape. You can use barbell weights and similar objects with a sizeable bulk.
Step 3. Let it dry in the sun
Leave the plywood with weights for 15 minutes before checking its progress. Keep checking until the plywood is no longer warped. Once you’re sure that the wood is already flat, you can take weights off and let the plywood dry.
How to prevent the plywood from warping
Plywood is prone to warping, but there’s something you can do to prevent it. Here are some tips to prevent damages to your pressure-treated wood:
- Store it flat. To prevent the plywood from warping, you should always store it flat. It will prevent one side from warping or losing its shape. If you’re worried about leaving the plywood on the floor, you can create a makeshift platform made of old timber.
- Use a rack. If you don’t have the space for flat storage, you can build a rack where you can stash your plywood supply. It should have enough support and must lean against the wall. You should ensure that the rack supports the plywood evenly, so its weight won’t cause warping.
- Seal the edges. Before storing the plywood, you should seal its edges right away. This is regardless if you’re going to cut it off in small pieces later. While you’re yet to use the wood, you should protect it from moisture that would cause warping.
- Control humidity. If you’re storing plywood in your workshop, you must keep the humidity at low to moderate levels. This will prevent the plywood materials from absorbing moisture in the air and warping in the long run.
- Place sticks between each one. To keep the plywood dry, you can place sticks in between each sheet. Make sure that the sticks support the plywood evenly so that warping won’t occur. This technique is very helpful for areas with hard-to-control humidity.
- Avoid oversupply. Since plywood is prone to warping, you should avoid storing too many sheets at a time. This way, you will have fresh materials for each project. Unless you have an environment-controlled storage area, you shouldn’t overstock with plywood.
Does all plywood warp?
All pressure-treated wood products are prone to warping. This is because pressure-treated wood has compressed wood chips in the middle sandwiched by a veneer. The compressed material in the middle is highly moisture absorbent. If your plywood material got soaked, it would likely warp if not dried the right way.
Nevertheless, plywood made for boating is often more durable than regular ones. It can still warp, but it will last long with proper sealing, even for high-moisture environments.
Always invest in premium plywood to reduce the risk of warping. You should also observe proper storage at all times.
Does painting plywood prevent warping?
Painting the edges of plywood is actually a good way to prevent warping. Paint has a waterproof characteristic that will seal the plywood grains against moisture. By reducing the plywood’s ability to absorb moisture, you’re also preventing it from warping.
However, painted plywood in use can still warp if exposed repeatedly to moisture and heat. As pressure-treated material, plywood isn’t the hardiest of all woodworking supplies.
Does varnish prevent warping?
The likes of varnish, lacquer, and shellac can all be used to prevent warping in plywood. This can seal the edges of the wood to prevent moisture from entering the grains. However, you should still store the plywood sheets properly to prevent one side from being lopsided.
What type of wood is least likely to warp?
All wood types, be it softwood or hardwood, will shrink to some degree. However, they vary widely, depending on the wood’s stability.
Redwood is so far one of the toughest timbers when it comes to moisture-induced warping. It has a straight grain pattern as well as a natural chemical that prevents excessive moisture infiltration.
Cedar is also a good choice if you want to avoid warping on your wood piece. It’s a dense wood that resists moisture and cracking.
How do you keep thin wood from warping?
If you’re working on thin wood, you must keep it dry all the time. If the wood is wet, you should dry it fast because drying too slow will allow moisture to infiltrate the grains and cause warping.
Also, you should watch out for high levels of humidity. While you’d want to keep the wood dry, you should also watch over cracking due to excessive dryness.
Does storing plywood vertically cause warping?
Putting plywood vertically against the wall should prevent warping. However, make sure that all sides and the middle have support to prevent it from sagging and warping. If your place tends to get flooded, it’s best to store plywood flat and elevated from the ground.
Will my plywood flooring warp?
As with any plywood products, plywood flooring will warp at some point. Make sure that you invest in high-quality plywood flooring for longevity. Also, you should not install this type of flooring on moisture-prone areas like kitchens and dining rooms.
Will plywood cabinet doors warp?
Panel warp is notorious for plywood cabinet doors. If your cabinets are exposed to high humidity levels, expect them to warp faster than usual. To prevent this, you should consider softwood or hardwood options that will last longer. However, these materials are more expensive.
Does plywood warp? It does, but there’s a way to prevent it and fix the damaged sheets. Just make sure that you store your plywood materials in a dry and well-ventilated area to prevent excessive moisture. Most of all, you should seal the edges to block moisture from getting into the pressure-treated grains.
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