Everything You Need to Know About Moisture and Timber

The common notion that water and wood can never mix isn’t really 100% accurate.

Why?

Well, because wood or timber actually has the ability to withstand and store water. After all, it is a hygroscopic material, which means it can both absorb and release water, if needed.

Everything You Need to Know About Moisture and Timber

The problem only arises when the wood takes in too much water or moisture. This is because if wood is too saturated with water, then it becomes unable to balance itself. When that happens, it then becomes vulnerable to potentially wood-destroying “elements,” such as fungi, microorganisms and others.

To make things clearer, let’s discuss the relationship between moisture and timber in detail:

Moisture Content or MC

As mentioned earlier, wood can withstand moisture and water provided that it is not oversaturated. And to know how much water it can withstand, we will need to understand moisture content.

MC is the measurement of how much water a particular piece of wood contains or is retaining. This is done by calculating the weight of the water with that of the wood when it’s oven-dry.

To get the percentage results, you just divide the weight of the water in the wood with the weight of the wood when it’s dry.

Example: If the result is 200%mc, then that signifies that the weight is doubled because of water, and not necessarily because of the density of the wood.

Take note: wood is considered dry if its moisture content is 19% or less. If it’s greater than 19%, it has been saturated with water.

Fibre Saturation

Fibre saturation is another important factor to take note of, most especially when it comes to determining wood shrinkage and decay.

Wood, as you may already know, is made of different fibres. These fibres are cells that compose a major part of the tree. Wood fibres actually resemble and function like drinking straws, as they absorb water once they get in contact with it.

These fibres store the water they absorb in the cell walls. However, if the walls become full and unable to store any additional water, then the water becomes retained in the wood’s tubular cells or cell cavities.

Note: water stored in cell walls is commonly referred to as “bound water.” On the other hand, water that’s been stored in the cavities of the tubular cells is called “free water.” Incidentally, free water is what fungi and organisms try to access in order to grow. In effect, it’s the one that we should measure and take note of.

That’s where fibre saturation comes into play.

As a rule, fibre saturation must be around 28%.

If the moisture content of a wood is above the average fibre saturation or above 28%, then it means that it’s vulnerable to decay.

It is also important to note that fibre saturation is the focal point for wood shrinkage, as wood will only change dimensions when its moisture content is below fibre saturation or below the average of 28%.

Why?

Remember that wood will swell or shrink depending on its moisture content. However, this will only happen if the water retained is “bound water” or stored within the cell walls. “Free water” or water that’s stored in the cell cavities will not affect the size of the wood. Note: if a wood’s fibre saturation is below 28%, then it means that it is storing “bound water.”

Equilibrium Moisture Content (EMC)

EMC is the point where the moisture content of a wood is stabilised. Usually, woods that are used indoors have an EMC of 8% to 14% moisture content. If wood is used outdoors, then its EMC is approximately at around 12% to 18%.

One of the main advantages of knowing EMC is that it actually gives you an idea as to how efficient your timber materials will be. Accordingly, wood or timber within the proper levels will release moisture if the atmosphere or air is dry and it will absorb moisture if the air is too humid. In effect, it balances everything out.

The problem arises only when the wood becomes too dry or when it reaches below the fibre saturation point. That is because it can lead to cracks, warping and other related wood problems.

To resolve this problem, it would be advisable to make use of timbers that possess the needed moisture content, as well as fibre saturation. This will reduce unwanted risks and will likewise keep things as efficient as they should be.

Do you want to use timber materials with the needed qualities and features? Call one of the top timber suppliers in Brisbane by dialing (07) 3888 1293.

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