Import Wood End Checking: How to Prevent 2024

There seems to be a correlation between the cost of an imported wood and the likelihood of it end-checking. Typically imported woods (exotics) are more expensive than their domestic counterparts. All too often they develop unsightly end checks rendering them difficult to market.

What Causes End Checks?

According to the Standard Grading Rules for Canadian Lumber, a check is a “separation of the wood normally occurring across or through the rings of annual growth and usually as a result of seasoning.”This defect is can happen to any wood specie, from mahogany to maple. Understanding the science behind what’s happening is key to preventing it.

Although seasoning is often the culprit, checking can occur as a result of environmental issues as well as issues related to the actual wood specie. The idea of eliminating end checking entirely is futile. The most we can expect is to keep it within a reasonable level. For the purposes of the article, I assume that we are dealing with either kiln dried or reasonably well air-dried lumber rather than green wood. 

Typically, checking results from wood that dries and shrinks at uneven rates. With end checking, this means that moisture is escaping out of the end grain of the wood much faster than the interior portion of the board. The ends move while the center of the board does not. Hence, the ends break free and check.

Why Are Imported Woods Prone to Checking?

There are several reasons why imported woods are prone to more end-check issues than domestic woods.

• Specie. First, certain species of wood are more likely to check than others. This is because wood is most likely to check along the rays. Thus, the woods with large rays, White Oak and North American Beech, for example, are the more likely to check than their smaller ray counterparts, such as White Hard Maple or American Cherry.  In terms of imported woods, Jatoba or Brazilian Cherry is more likely to check than Genuine Mahogany, for example.

• Board Size. Many imported woods are sawn at relatively large sizes. We often find 15″ inch wide Mahogany boards. Occasionally, this results in the board not equalizing consistently and developing checks, twists and splits. The edges of the board may be drying out from wind exposure while the center remains at a higher moisture content, for example. In smaller boards, variation in moisture content across different areas of the board is typically minimal and not enough to create stress resulting in checks. 
• Kiln Drying. The quality and method of kiln drying affects wood stability and thus, likelihood of checking.

Different kiln drying standards. 

Woodworkers often assume that wood is kiln dried to the same standard regardless of its country of origin. However, the main purpose of kiln drying is to bring wood down to a workable level. Workable means different things to cultures. The one wood drying principal that is universal is that over-drying causes honeycomb and ruins the wood. With that in mind, kiln operators are unlikely to push the envelope to reduce that last 2-3% of  moisture if they don’t have to. Less sophisticated high volume kiln operations have even less margin for error.  Additionally some timber export destinations have their own moisture content standard. For example,  Europe’s preferred moisture content for kiln-dried woods is 12-15% compared to 6-8% in the United States. . This is because their overall climate is wetter than ours.  Much of the imported lumber that comes into the Unites States is actually dried to European specifications.  Some US companies re-dry their imported woods to US standards after arrival. However, many companies skip that step and market the product as soon as it lands.