It is weird to think that wood moves and that it will never stop moving. No matter how old or new it is, if it has been sealed or treated, or if you fasten it, you cannot stop the movement of wood. Understanding the ins and outs of wood movement is essential before you begin working with it no matter the project or the type of lumber you are using.

One thing to keep in mind is that wood movement varies among different species. Knowing these variables will help you tolerate the movement of wood much easier when you are working with it.

Why the Movement of Wood happens

To get a visual perception of the movement of wood, think of it as a bundle of straws. While a tree grows it sucks up water through these straws and distributes it throughout the tree.

When a tree is cut down, water still resides in these straws. This is why it important to acclimate wood before working with it. This water will eventually dry up and this will change the dimensions of the wood. This reverse it true when the tree absorbs water as well.

The acclimation process eventually stops this from happening because the tree then becomes equalized with the moisture or humidity in the air. This expansion and contraction can be sped up with kiln drying, sealing, and finishing. Once these processes are complete there will still be some movement to take into consideration. There are charts available that give specific technical data per species, so you know what to expect.

When it comes to the expanding and contracting of wood, shrinkage is the most important thing to consider. This will affect fastening sites and any project where lumber needs to “fit” into a specified space.

The Two Types of Shrinkage in the Movement of Wood:

Tangential Shrinkage: This refers to the movement that occurs around the growth rings. Think of it as the swelling of a straw from side to side when it fills with water.  This is where most of the movement of wood takes place.

Radial Shrinkage: This refers to perpendicular movement. Although this encompasses only a small amount of overall change, it should be accounted for.

Now, with this basic movement of wood knowledge, you can successfully work with flooring, decking, windows, and doors. Just remember that the movement of wood does not occur uniformly within one single piece of wood depending on density. It is this differential movement that causes twisting, warping, and other formation changes.

Here are some simple ways to reduce the amount of movement in any type of wood prior to a project or installation:

  • Do not leave wood out in direct sunlight as this will speed up the “dry out” process. The wood will then expand after it is out of the extreme heat giving you false measurements.
  • Use racks and pallets to store your wood off of the ground so it does not absorb any unexpected moisture.
  • Always follow the acclimation advice specific to the type of wood that you are working with.
  • If you have the option, purchase kiln dried wood so that you know what moisture level your lumber is starting at when you purchase it.

 

The long and short of it is that wood is an organic material and although there are things to do to prevent major expansion and contraction it cannot be stopped completely. This will not stop you from accomplishing your desired project and will ensure that you know what movement you can expect. If you are looking to start a project but don’t know what species of wood to work with, give us a call! Our knowledgeable staff can walk you through what options are available to you as well as offering you some of the best prices in the industry!