How Seasonal Changes Affect Wood Treatment, Drying Times
Protecting the integrity of the product is a constant concern at any lumber mill. That’s why mill personnel are expected to carefully track wood moisture content and follow dry kiln schedules to the letter.
These details require even more attention during transitions between seasons, as temperatures and humidity can vary quickly and unexpectedly, such as the transition between spring and summer. At these times, kiln operators may often begin to see charges of lumber coming out of the kiln with average moisture content (MC) readings significantly higher or lower than their target MC. They must be prepared to make quick, last-minute adjustments to kiln schedules, obviously making it critical that the instrumentation is as accurate and reliable as possible.
In addition to adjusting kiln schedules, however, it’s also important to remember green lumber is vulnerable to damage while in storage, stacked on its stickers prior to going in the kiln.
Here are some things to keep your eyes out for as the weather starts changing, as well as methods for avoiding damage during storage or drying.
Potential Seasonal Causes of Wood Problems
If outside temperatures are below freezing, there is no discernable movement in moisture. But as temperatures rise, moisture in the wood will start to slowly move toward the surface of the wood as it loses moisture to equilibrate with the air.
Often, if lumber dries too rapidly, warping, twisting and other unwanted distortions can occur.
In regions with relatively low humidity and higher wind speeds, mill personnel should be wary of damage to stacked lumber that is being stored prior to kiln drying. The boards could lose moisture content too rapidly and experience end splitting, where the surface and edges dry significantly faster than the inside of the board. This stresses the boards and can also cause warping. You may also notice checks or shaking on the ends or faces of the boards from losing moisture too quickly.
High Humidity or Low Airflow
Especially in places that experience higher humidity during the summers, fungal growth and staining are common concerns. These issues can be exacerbated if the wood is stored in an area with low air flow.
Short-term storage between kiln drying is ideal in these conditions, leaving less time for the wood to absorb moisture from the air. Insect infestation is also less of a worry since any bugs or unhatched eggs will not survive the kiln-drying process.
Additional Ways to Protect Lumber in the Yard Before Drying
Managing the moisture content of commercial lumber is an already tedious process, even before considering the unpredictability of seasonal transitions. That’s why every precaution that can be taken out in the yard will help kiln operators develop an effective schedule to produce the highest-graded lumber possible.
Over the years, mill workers have developed several methods and treatments to help prevent lumber degrade such as splits, discoloration, or insect damage while the boards await the kiln.
Many mills typically apply a wax-like product such as the well-respected Anchorseal®, or a similar compound, to the ends of logs or boards. It is often sprayed on the ends of wood after it is sawn into dimensional stock.
Some mills coat logs upon arrival, especially if economic reasons make it necessary to stockpile logs to be sawn later. In many of these cases, fungicide is also sprayed on the logs before the sealer is applied.
In addition to end coating, mills may opt for a controlled air-drying process before kiln drying. This slowly brings the lumber moisture content down from green to close to fiber saturation point, to prevent internal defects that would otherwise show up because of drying too fast. Typically, the lumber is placed in a pre-dry building with fans continuously blowing air across the stacks of lumber.
Sprinkling Logs with Water
In some parts of the country, mill personnel sprinkle log decks with water to help protect lumber from developing defects before it is kiln-dried. It also helps curb insect infestation and fungal growth. It’s harder for insects to lay eggs on the wet logs, and fungal spores need air as well as moisture to get established.
In western areas during summertime, some pine-producing mills will also use water sprinkling to retard blue staining from a specific kind of fungi.
At some eastern lumber mills, it’s common to freeze birch, maple and pine logs about to be sawn into boards earmarked as specialty products. This ensures a white color.
The short logs from winter-cut timber are placed in ground depressions and sprayed with water to form a coating of ice. The frozen log decks are covered with sawdust, wood shavings, or other available insulating material so the wood remains frozen well into the summer months when further processing begins.
Maintaining a Thorough Routine of Quality Control and Moisture Testing
Every day is filled with calculating, tedious work for mill personnel and kiln operators. The effective processing of pre-kiln timber is challenging enough even before considering the potentially erratic and unpredictable weather changes that can happen during transitions between seasons.
Most major lumber mills in the world not only utilize handheld moisture meters for spot-checking lumber but also have in-process moisture measurement systems installed in or on the lumber conveyance machinery to continuously measure the full length of every piece of lumber as it is being processed. Additionally, many mills also now take advantage of In-Kiln moisture measurement systems to monitor the moisture content of a few packs of lumber in every kiln charge, helping them better determine when charges of lumber are ready to come out of the kiln.
If mill personnel make it a priority to run a tight ship in terms of moisture testing, using quality tools, and carefully noting what ambient conditions could require additional attention within an existing routine or procedure, odds are good that they will continue to turn out a quality product that will sustain their reputation within the industry.
Make sure you have the best wood moisture meters in the industry! Learn more about different types of wood moisture meters and systems and which type of meter is best for your application. Have questions? Give us a call at (541) 291-5125.
Want a discreet and reliable way to monitor and report ambient temperature and humidity readings around your wood? Check out the Smart Logger™.
As Sales Manager for Wagner Meters, Ron has more than 35 years of experience with instrumentation and measurement systems in different industries. In previous positions, he has served as Regional Sales Manager, Product and Projects Manager, and Sales Manager for manufacturers involved in measurement instrumentation.