Kiln-drying is a process whereby unmilled logs are placed in a chamber that slowly raises the logs temperature to over 170 degrees for a period of up to 28 days. This removes over 1400 gallons of water (10,000 lbs) from the a typical log home lowering the moisture content of the logs from over 30% to less than 20%. The process uniformly shrinks and stabilizes the logs and minimizes the checking associated with un-dried logs. The important thing is that with kiln-drying, the shrinkage occurs before the logs are milled and stacked up as the wall of your new log home. While removing 10% -20% of a logs moisture may not seem

like much, it is the difference between a stable wall and a wall that will shrink 2-4 inches over a few years time. Why not remove all of the moisture in a log? The naturally occurring humidity in most climates raises the moisture content of the log back to around 19% . In addition, that much drying would destroy the logs with excessive cracking.

 

A Brilliant Solution... a "Settling System"

You may be thinking "a green log wall will shrink 2-4" over a few years, isn't that bad? Yes it's horrendous. The industry

term is called "settling" and it creates all kinds of complicated problems that you will have to struggle with for years to come if you build with green logs. It's the industry's dirty little secret and thousands of folks live with it daily because they purchased green logs from a supposedly reputable company. How and why do they do this? The answer is simple: Money and more money. Kilns are expensive to build and operate, in fact I estimate better than 75% of log companies (including some of the largest and best known national manufacturers) do not kiln-dry because it adds more than 10% to the cost of manufacturing (or 10% less to the profit margin.) Ok, but how do they perpetrate this farce with thousands of customers every

year? Their brilliant solution, a "Settling system". Yes folks, they have a sophisticated little hoax called a settling

system. Oh it makes perfect sense in theory. It sounds so good you can sell it to the best educated of folks. The problem is that they are so complicated to install that the vast majority fail. The bottom line is that with green (or air-dried) logs, the walls on the outside perimeter of your home are going to shrink (settle) 2-4 inches over a few years due to the cumulative effect of the stacked logs shrinking from moisture loss. The rest of the components that are connected to the walls are not going to shrink (i.e. the posts holding up your second floor system and porch roof system.) This includes the windows and doors and anywhere that something is attached to the outside walls (partitions, trim, cabinets, etc.) So the brilliant hoodwinkers in engineering created this complicated series of gadgets like adjustable post screw jacks, sliding window and door bucks, floating trim and partitions and through-bolted wall rods that have nuts and washers on the bottom so you can crawl under the home every few months and tighten it back down. This all adds several thousands of dollars in cost to the

homeowner in both additional hardware and labor to install. The reality is that most builders haven't the foggiest idea what it takes to install all this nonsense so that it actually works right and very few do. The result is a nightmare of shrinkage, settling, air, moisture & bug infiltration problems to mention a few as well as years of work trying to adjust and correct the resulting problems. Yes Virginia, Kiln-drying does solve all of these problems from the start

 

Additional Benefits of Kiln-Drying

 

Sterilization. If you ever get the chance to see the inside of a kiln that has just been emptied of its log contents,

you will immediately notice the disgusting layer of dead bugs on the floor. The heat used in kiln-drying kills the

insects and their eggs that normally inhabit log cants (including termites and wood boring beetles.) You can guess

where the bugs end up in logs that are not kiln-dried.

Sap Crystallization. Sap seeps out of green logs over time making a sticky mess on the outside of your logs.

Sap is permanently crystallized in kiln-dried logs.

Preservative/Finish absorption Green logs will not absorb preservatives and wood finishes as deeply as

kiln-dried logs will meaning your finish will not perform as well. As mentioned earlier, thousands of pounds of water are removed from kiln-dried logs making them

about a third lighter. That means your 300 lb log will only weigh about 200 lbs which is allot easier for two men

to handle

 

Kiln Drying

 

The moisture laden air is removed from the kiln by way of an automatic ventilation system. The drying

rate of the timbers is carefully monitored because the outside perimeters of the cants naturally tend to

dry faster than the centers. Uncorrected, this imbalance would cause severe checking (cracking), so

the final stage of kiln-drying large timbers requires a steaming process. This adds moisture to the

outside portions equalizing the moisture throughout the wood.

 

As mentioned earlier, kiln-drying lumber is a science. It is not a random act of loading material in a

kiln, flicking a switch, and coming back at some later time to retrieve it when a timer rings. It is a

carefully monitored procedure. Before the lumber is placed in the kiln, a kiln schedule must be

prepared. This schedule will outline the different sets of conditions to be carefully followed in order to

achieve the desired moisture content, without damaging the wood. The kiln operator will modify the

conditions in stages based on the moisture content of the lumber or by time-intervals. Sample logs in

the kiln are connected to sensitive measuring devices outside the kiln chamber, and monitored for

temperature and moisture content. Once it has been determined that the desired moisture content

(19%) has been achieved, cross-section samples are taken from the center of randomly selected

cants in the kiln, and tested.

 

Moisture content of the timbers can be measured in a variety of ways, however, the most accurate

method is by use of the "oven-dry-ratio" analysis. This is done by first weighing the kiln-dried sample

on a set of sensitive gram scales, then drying them down completely in a small oven. The ratio

between the original kiln-dried weight and the final oven-dried weight represents the moisture content

of the timber, inside and out. Another device used to measure moisture is the moisture probe, which

measures only the outer fractional portion of the timber. It can not penetrate the wood deep enough to

give an accurate reading of the moisture content throughout the log, but only the outer portion, which

will tend to be the driest portion of the timber.

 

After testing to verify the desired moisture content (average 19%), the cants are removed from the kiln,

ready for milling to the finished log profile. This process of drying a green 6"x 8" timber generally

requires a 4 to 6 week period (on average) in the kiln, to achieve the 19% moisture content.

 

Kiln-drying provides several very important benefits; primarily, it produces logs that are uniform and

stabilized to match the actual home environment. Wood must be conditioned to the moisture content it

will assume during it's service life. Otherwise, it will have a tendency to shrink and twist to some

degree. Since the exterior wall normally will range 10%-30% moisture content throughout their yearly

cycles, kiln-dried logs, at 19% moisture content are as dimensionally stable as possible for most

areas. Companies that kiln-dry their material down to an average 19% have the advantage of removing

logs that exhibit severe stress changes such as splitting and warping, prior to the final milling and

grading processes. The customer can see the final beauty and integrity of each log before it is placed

in the wall, and not have to worry about what the home is going to look like after the logs have finally

dried-out.

 

 

Have you also considered that non-kiln-dried (under 160 degrees F) pine wood will ooze sap?

 

 

I have experimented with drying timbers quite a lot and have one trick to pass on: You will get more checking in

the timbers if the heart is still in them.

 

What you say about using free-of-heart timbers is a very good idea to prevent the inevitable checking that happens

to air-dried, boxed-heart timbers. The only other aspect that you might want to consider is having the timbers cut

with four faces showing vertical grain.

 

We use this configuration on all of our structural timbers, and have had very few problems associated with

differential shrinkage.

  

Dry Kiln Operators Manual

 

 

This section suggests methods for reducing drying defects that result from prolonged storage of logs. Logs need to be

stored under conditions that will minimize defects associated with shrinkage, mainly

end checking, and attacks by fungi, bacteria, and insects. Defects associated with

shrinkage are minimal during periods of cloudy, wet weather and low temperatures.

Fungi and insects are inactive at temperatures below 32 °F or under conditions of wet

storage with low levels of oxygen. On the other hand, many types of bacteria can

grow in wood under wet, anaerobic conditions, but not at subfreezing temperatures.

There are two general methods for storing logs dry storage and wet storage.

Precautions must be taken with each storage method to ensure defect-free lumber.

Most sawlogs in North America are stored under dry conditions with the bark intact.