As many Kansas City deck builders know well, his time of year always brings surging inquisition from customers about small cracks appearing in their wood decking components. Most people are initially very concerned about this natural process often found in wood called “checking.” That is until we explain what checking is, why it occurs, what can be done to slow it down and how to help conceal its effects, if so desired.
As I said earlier, we field many more calls about checking on our wood decks and components during the fall and winter months. The reason is very simple. It’s directly related to the sudden drop in temperature, and in turn, the drastically decreasing humidity levels in the atmoshphere. It’s the same reason you need to crank up the humidifier in your home as the weather gets cooler. If not, your skin is also more likely to get cracked, itchy and irritated due to the surrounding air sucking the water right out of your body.
Make no mistake, I’m just a professional deck builder in Kansas City. That’s about as far from a doctor, biologist or scientist as you can get. Nonetheless, I’ll give you what I know about checking, why it happens, and how to combat the wood’s natural process. My experience is with lumber used in deck duilding. However, much of will overlap just about any application pertaining to wood.
“What is “Checking?”
As wood begins to dry out, it usually develops natural cracks called “checks.” Checking happens as moisture is released from the wood’s outer rings at a faster rate than its inner rings.
“A check is a naturally occurring lengthwise separation between wood fibers parallel to the grain.”
- © 1997 The APA – The Engineered Wood Association –
Checking, the separation of continuous wood fibers, is a naturally occurring consequence of the seasoning process of wood. The outer fibers lose moisture to the surrounding atmosphere and attempt to shrink, but the inner portion of the timber member loses moisture at a much slower rate. The different rates of shrinkage can cause the wood to check or split. Rapid drying increases the differential moisture content between the inner and outer fibers and thus increases the propensity for checking in the timber. The checking (and shrinkage) process will stabilize as the moisture content of the member reaches equilibrium with the surrounding environmental conditions.”
- © 2009 APA – The Engineered Wood Association -
“Why does it occur?”
Checking is more prominent in larger timbers and less porous woods. Larger timbers and dense woods are prominent in the construction of decks in Kansas City and many regions throughout the United States. Both of these characteristics delay the rate at which wood’s core moisture evaporates compared to its outer shell. While larger sizes and denser woods are more prone to check, this natural phenomenon can appear in almost any dimension or species of wood.
The amount of checking greatly depends on how fast the wood dries out. Kansas City’s extreme variance in temperatures creates an ideal environment to produce wood checking. No matter what the climate conditions or surrounding air temperature, checking can and probably will show up at some point.
Below are some pictures of profound checking which popped up on the pergola in our back showroom. Keep in mind, this in Western Red Cedar. Cedar is not only very porous but is also widely recognized as one of the more stable wood species. Nonetheless, substantial checking still happened. Not to mention, this display was built and has always been kept indoors with a temperature variance of never more than five degrees Fahrenheit.
Many homeowners and novice deck builders erroneously misinterpret wood checking as the beginning of wood deterioration. The truth is, checking has no affect on the structure, strength, or durability of wood. Checking rarely penetrates further than the heart or center of a log, timber, or board.
As a matter of fact, many top designers, architects, and deck builders request wood containing checks for a more natural look.
“What can be done to prevent it?”
There is no cure or way or absolute way to prevent checking. It can be slowed by staining, sealing or painting the wood. This will help retain moisture in the outer layers longer. Thus allowing the wood to dry more evenly throughout, and therefore, separate less.
If checking seems unsightly, you can fill the gapping with an elastomeric caulk or epoxy. When filling wood which is kept outdoors, it is recommended to follow with paint, lacquer, or poly urethane. This will help prevent separation of the filler from wood after more exposure to the elements.
Fore more info on “Wood Checking,” visit the following links:
http://www.apawood.org/glu_level_b.cfm?content=prd_glu_gen_check
http://www.wvu.edu/~exten/infores/pubs/other/wooddr2.pdf
http://northernloghome.com/checking.htm
Hope this helps,
Dan Milford (DW Elite Decks – Kansas City deck builder)
