Checking and Cracking in Wood Timbers:

What Is Timber Checking?

“Checking” refers to cracks or splits that run along the grain of a timber as it dries and shrinks. These checks can be shallow or deep and are one of the most common and natural characteristics of real wood timbers.

In properly sized structural timbers, normal checking is expected and does not reduce structural strength. It is primarily a visual change and often becomes part of the timber’s natural character.  It is not a defect in the timber. 

 

Why Timbers Check:

• Moisture and drying: Wood expands and contracts as it gains and loses moisture. The outside of a timber dries and shrinks faster than the interior, which creates tension and results in checks.
• Sun and weather: Sun, wind, and UV exposure speed up surface drying, especially on exposed faces, which can increase visible checking.
• Temperature swings: Large day‑night or seasonal temperature changes accelerate drying and movement in the wood.
• Grade and heart center: Lower grades and pieces that include the heart (center) of the tree are more prone to checking. Premium “Free of Heart Center” (FOHC) timbers typically check less, but checking cannot be eliminated completely.
• Size and thickness: Larger, thicker timbers are more likely to show pronounced checks because of the moisture difference between the surface and the core.
• Internal stress and fasteners: As the wood relieves internal stresses, it will check. In most cases, this stress relief is beneficial long‑term. Poorly placed fasteners can create localized checking.

 

How To Reduce (Not Eliminate) Checking:

Checking can be minimized but not fully prevented. Helpful practices include:

• Sealing timber ends with a wax or end‑grain sealer.
• Storing timbers off the ground, in shade, with good air flow.
• Choosing higher‑grade timbers (such as FOHC) when appearance is critical.
• Applying quality UV‑resistant stains or finishes and maintaining them over time.
• Designing and fastening so that major checks are less visible and not driven by fasteners.

 

Reasonable Expectations:

Some checking will occur in almost every timber installation over time. It is:

• Natural, not a defect.
• Extremely difficult and costly to prevent.
• Typically cosmetic rather than structural.

If you are not expecting wood to move and check, it can be surprising or frustrating the first time you see it. Our goal is to set clear expectations up front so that, as your project seasons, these checks are understood as part of the natural beauty and uniqueness of real wood timbers—not as a quality issue or reason for concern.