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Kiln drying is the most essential step in manufacturing wood flooring. This is as true with antique wood. Why? Because if it has not been dried properly, expansion and humidity will cause serious shifting and other damage to your flooring. Following is information that will help you understand the importance of kiln drying: how moisture effects harvested wood, what is considered an acceptable moisture content and why, and some pre-installation warnings and other practical information to help you prepare for your new hardwood flooring.

1. How moisture effects harvested wood:
Live wood is saturated with water. Immediately upon cutting down, the moisture content level ("MCL") begins decreasing. Because of the water content, the wood will naturally warp, twist and buckle. It is not ready for manufacturing until that MCL has been reduced to at least 18%, antique wood even a lower ratio at 10%. Without technological intervention, that will take months (sometimes years depending on the species) to happen.
Wood is hygroscopic – it will absorb the moisture in its environment until it has reached equilibrium, whether exposed to the elements or installed in your home. Even though reclaimed wood was dried, or seasoned, before construction many years ago, because it has been exposed to nature and the elements for so long, naturally it's MCL has increased enough that it is not ready for the milling process. Wood that we purchase for inventory is generally between 22-30% MCL. The wood must go through a drying procedure before it can be cut to our client's specifications.

In flooring form, after the milling process, a continued exposure to water can cause cracking (caused by the expansion-shrinkage cycle triggered by high/low humidity changes from summer to winter), cupping (warps upward like an upside down cup) and buckling (more complex warping then cupping). Wood often moves or shifts due to water absorption, too. These problems can be reduced (never 100% prevented) by proper kiln drying prior to milling and installation.

2. What is considered an acceptable moisture content and why:
Wood begins to shrink at 25-30% MCL, and it will continue shrinking until the MCL is 0% - yes, even after it has been installed as flooring. Some species handle shrinkage better, but there is indeed no realistic way to avoid it. It generally will not stop either, even after years have passed. You can, however, drastically reduce the consequential damage by drying it properly.

The ideal MCL according to N.W.F.A. (National Wood Flooring Association) guidelines is 4-18%, depending on species and geography. AASW brings the MCL of our reclaimed wood to 6-9%. Although we use advanced gauging tools, the MCL is otherwise calculated as follows:

(weight of wood before drying – weight of wood after drying)
weight of wood after drying

3. Pre-installation warnings to help prepare for your new hardwood flooring:
While your wood is being manufactured, you must prepare the installation space for its arrival. Whether a small restoration project or a full-scale new home, heed these warnings. Do not install your flooring until:
- Construction dampness has dissipated.
- Roofing is completed.
- Windows and doors have been installed at least 30 days.
- Plastering or cement work is completed.
- Your home humidity range is 30-50%.
- Your temperature has been 60-80° for two weeks.
The flooring will also have to sit in your home prior to installation (as long as the above guidelines have been met) for a period of at least one week.  This allows the wood to become acclimated to its new environment and do the expanding/shrinking before installation.
Remember that flooring is considered interior finish work. Prevent damage caused by laborers still in building phases from causing damage to your fine wood floors. Listen to the recommendations of your general contractor or engineer.
Expect even a little expansion after installation. It's the nature of wood.  To reduce damage caused by shrinkage-expansion, we highly recommend humidity control. The humidity range should be maintained between 30-50%, and temperatures should not exceed the range of 60-80°. A simple 10% deviation from these ranges could cause a 1-2" shift in your planks. If your house is not climate controlled, we highly suggest investing in humidifiers to help you maintain these levels.
The wider your boards, the more movement you will get. The look of wide-width flooring boards is marvelous and preferred by most wood aficionados, but be forewarned that they will move more than standard widths.
As always, make sure your house has adequate drainage and ventilation. This is not such a concern with new construction since your architects and builders have carefully addressed this, however it is always a good idea to be a wary consumer. We recommend a moisture barrier over sub-flooring, but this is to be discussed with your installer or architect.

Does AWPF Kiln Dry Wood?
Absolutely. AASW stores its inventory in cool, dry locations and will kiln dry the wood just before it is to be milled. Antique wood should be kiln dried only when it is ready for the cutting process, never before purchase.
We have set-up a highly sophisticated kiln to dry wood slowly and carefully. The process is never rushed. Without giving away any trade secrets, we have compiled a system that reduces the MCL to wood industry guidelines in a manner that will help reduce expansion-shrinkage after installation by implementing proven heating and circulation systems. After the milling process is complete, we check the planks’ MCL again during our finishing process to make sure it has met our high standards and is ready to be installed as fantastic hardwood flooring.