What to Expect with KDAT (Kiln Dried After Treatment) Lumber

KDAT Brown from Northern Crossarm Co., Inc.

Wood is a porous material, which makes it ideal for the pressure treating process. Because it is porous, wood has a natural tendency to warp, cup, twist, crack, check, shrink and swell as it is exposed to wetting and drying cycles.

The pressure treating process fully saturates wood with preservative and water. While the preservative is left in the wood for protection, the water is released as the wood naturally dries, bringing out these natural characteristics.

Kiln Dried After Treatment, “KDAT” is a process that removes this excess moisture from wood introduced by the treating process. Kiln drying after treatment helps to improve the performance and stability of pressure treated wood.

KDAT Benefits:

  • Lighter, easier to handle.
  • More resistant to shrink, cup & warp.
  • Easier to saw & plane.
  • Better holding power (nails & screws).
  • AG, GC & Fresh Water Immersion.
  • Can be painted or stained immediately.
  • Better corrosion resistance for exterior code-approved fasteners & hardware.

KDAT is Still Pressure Treated Wood.

While the KDAT process helps to improve the stability of pressure treated wood, it does not make it impervious to wood’s natural characteristics. This is especially true if it is exposed to wetting and dry cycles prior to installation.

What Not To Expect?

Strict Uniformity – Sawn lumber will vary in dimensional size due to mill inconsistencies. KDAT can only restore lumber sizes close to their beginning size. IT IS NOT EXACT.

Exact Moisture Content – When lumber is KDAT, a moisture range of (125%-19%) is targeted. KDAT is not an exact science, and lumber will have variations in moisture content. Moisture variations will become considerable, if the lumber is exposed to moisture after being Kiln Dried After Treatment.

Elimination of All Natural Characteristics – While KDAT improves the performance of treated lumber, it cannot eliminate these natural characteristics completely. Some warp, cup, twist, check, crack, shrink and swell is to be expected.

Because wood absorbs moisture and swells when exposed to moisture, proper spacing between deck boards is important during construction when using KDAT decking. A gap of approximately 3/8″ between boards allows for expansion.