At this point in our discussion of the varying North American and European moisture content standards for kiln-dried lumber (see Parts 1 & 2), it may behoove us to look at why kiln drying is so important in the first place. What exactly does it accomplish? That will be our next topic to explore.
What’s So Important About Kiln Drying Lumber Anyway?
When lumber is kiln-dried, the wood’s cell walls become much harder. By way of illustration, it’s similar to toasting a piece of bread. When you’re going to use lumber in a dry North American climate, those few percentages of extra drying and the stabilization they represent can make a big difference. Much of that stabilization takes place after the lumber reaches an 8% moisture content.
When lumber comes out of the kilns, it starts to gain and retain moisture once again. This is especially true for lumber yards in wetter coastal regions where the moisture content equilibrium is closer to the European Standards. So why, you might wonder, would dealers even bother with the extra kiln drying in the first place? It’s because of the hardening of cell walls that this lower drying will accomplish. It changes the rate at which lumber will pick up or get rid of moisture from that point on, making it easier for the wood to acclimate to a dry climate later on.
Once the lumber has gotten down to North American standards through kiln drying, it should perform better even if it ends up somewhere like Arizona. Without this extra step, the wood could easily bow, warp, or twist if it’s used in a dry climate and it ever encounters some precipitation. What would happen in that situation is that while the moisture in the air would temporarily rise, the lumber’s moisture content wouldn’t gain too much moisture content. This increased stability will keep your lumber from experiencing too much movement. This is especially helpful if you use it for flooring, trim, walls, or in exterior applications. If the percentage of moisture in the lumber does begin to rise, it most likely won’t do so in a quick, dramatic fashion. This gradual drying should keep the wood from sustaining damage.
The reason you should be aware of the different moisture content standards for European and North American lumber is that it can have an impact on the quality and the price of the lumber you buy. If you want lumber that is high quality and stable, you’ll probably have to be willing to pay a little extra for materials. But think about it as a short term investment that will end up saving you money in the long run. If you use a product that has not been properly prepared through extra kiln drying, you run the risk of it warping and cracking in the future.
It’s certainly worth it to ask your lumber supplier if they kiln dry their lumber down to North American standards. This is very important as more and more lumber yards start offering African hardwoods. You want to be sure that they’re taking necessary quality control measures.