Plywood is an extremely versatile type of timber that has many uses in several building applications. It is made using several layers of softwood compressed together with glue. The grain of each layer faces a different direction, adding to the overall strength of the wood.
Due to being made up of layers of wood and glue, plywood will warp if exposed to moisture for extended periods. Plywood must be stored correctly and kept away from any moisture sources to avoid warping. This will ensure that the timber maintains its integrity and remains usable.
To prevent your plywood from warping, there are several measures you need to take. This includes the correct storage of the wood and ensuring that there are no sources of moisture located nearby. If plywood becomes wet, there are numerous methods to return it to a usable state.
Does Plywood Warp When Wet?
Due to how it is made, plywood has a tendency to warp whenever exposed to moisture for prolonged periods. Because it is made of timber, plywood is highly absorbent of moisture.
Its ability to absorb moisture is particularly prevalent on the ends of the boards, where there are significant pits and exposed grain. This is where moisture is absorbed the quickest, so extra care should be taken to ensure that moisture cannot gain access to these timber parts.
Bear in mind that plywood won’t warp as badly as lumber does, making it a better choice in this regard. Certain types of plywood are made with a lumber core, so this type of plywood will naturally be more susceptible to warping whenever exposed to moisture.
Why Does Plywood Warp?
Generally speaking, plywood warps due to the combination of moisture and heat. If you examine a piece of warped plywood, you will notice a convex side and a concave side. The concave side of the plywood will have more moisture than the convex side.
This difference in the moisture levels on the two sides of the plywood will result in warping. This discrepancy in moisture can occur if the plywood sits in the sun, causing the exposed side to dry out. At the same time, the underside retains a significant amount of moisture. The sun causes the humidity to leave the wood.
When there is moisture present, the excess humidity in the surrounding air is absorbed by the grain, resulting in warping.
Significant changes in temperatures and humidity levels can cause the glue in plywood to weaken, contributing to the warping of the plywood. Besides the warping caused by changes in moisture, there are several different ways in which the warping of plywood can occur.
Gravity is one such cause of warping in plywood. Suppose the plywood sheets are placed on an uneven surface. In that case, the weight of the board itself, combined with the level changes in the uneven surface below, will cause the plywood to warp.
Placing too much weight on plywood in a section that is not adequately supported can also result in warping to a large degree.
Suppose the space in which your plywood is stored lacks sufficient ventilation. In that case, the accumulated moisture in the air that cannot move due to insufficient ventilation will cause the plywood to warp. While this is an issue that is relatively easy to fix, it must be addressed as soon as it becomes an issue.
How To Prevent Plywood From Warping
While the warping of plywood can occur relatively easily, it is just as easy to prevent it from occurring in the first place. One of the best ways to prevent warping is to avoid storing it on edge. Plywood stored on edge will start to bend and warp under its own weight with time.
Resultantly, the best way to store plywood is to store it flat. This can be achieved by creating a platform for the plywood to sit on. You should always remember that the platform needs to develop proper support for the plywood sheets and not just support it on its ends.
If the plywood is only supported on its ends, it will start to sag in the middle, resulting in warped plywood. Use four or five stringers across the length of the board to achieve sufficient support for the board.
If it’s not possible to lay the plywood flat, it can be stored upright using a rack. As long as lateral support is provided up the entire height of the sheet as it stands upright, no lateral warping can occur.
Another way to prevent the plywood from warping is to seal its edges. This is especially true of the end grain, as this is the area where moisture is absorbed the quickest. To ensure proper sealing of the ends, paint on several coats of sealant until there are no more visible pits on the ends of the timber.
Which Type Of Plywood Doesn’t Warp?
While there is no such thing as plywood that doesn’t warp whatsoever, some types of plywood are more resistant to warping.
Marine plywood doesn’t warp as easily as the other types of plywood. It is engineered to be free of voids. It is also pressure treated. The combination of the lack of voids and the pressure treatment results in plywood that is exceptionally resistant to warping and rotting.
Cabinet-grade plywood is generally void-free, making it less prone to warping. This is especially true with higher numbers of veneer layers. Pressure treatment will ensure that the wood is less likely to absorb moisture. This means that it is less likely to warp.
Conclusion
Unfortunately, the nature of plywood causes it to warp if it is exposed to moisture for extended periods. Several preventative measures can be taken to prevent the warping of this all-purpose timber. However, if it does happen to warp, it is possible to straighten it out to make use of it.
Plywood is extremely versatile and user-friendly because it can be bent back into place despite being warped.
Sources
https://www.woodweb.com/knowledge_base/Why_Does_Plywood_Warp.html
https://www.roofingmegastore.co.uk/blog/plywood-will-water-ruin-it.html
https://thetoolsmag.com/how-to-prevent-plywood-from-warping/
