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Lessons Learned As mentioned earlier, stainless steel fasteners and hardware should be used. Failure to use stainless steel will result in premature failure of the hardware and the potential for stained or discolored lumber. Alternative construction materials for some portions of the current design may be more desirable. One example would be to use impermeable wall insulation such as a spray applied closed cell foam system to limit in-wall moisture penetration. Moisture loss through the kiln structure was noticed at the end of the drying cycle as the lumber moisture content continued to decrease but no condensate was collected from the dehumidifier. As constructed, the kiln doors are large and heavy. One alternative is to buy or build a structurally insulated panel. These panels consist of rigid foam sandwiched between two sheets of a wood panel product such as plywood or oriented strand board. This design would make a much lighter door panel and provide superior insulation. PREPARING THE LUMBER End coat the green lumber with a commercial end coating immediately after sawing to prevent large losses from end checks and splits. End coating is less effective when applied after the lumber has begun to dry. The end coated lumber should then be stacked in the kiln with approximately 12 inches of clearance on the front side of the stack and approximately 30 inches of clearance on the rear side of the stack (dehumidifier side) to permit adequate air circulation. These spaces are known as plenum spaces. Arrange the lumber in neat layers, separated by stickers or spacers running perpendicular to the lumber’s length. The lumber in each layer must be uniform in thickness. If the sawn lumber is quite variable in thickness, one or both faces of the boards should be planed before drying to obtain a uniform thickness. This will reduce warping during drying. Particularly in warmer months, green lumber should be stacked with stickers quickly after sawing or it may begin to develop stain – an undesirable and highly visual defect. Stickers used between each layer of wood are typically three-quarter inch thick, one-and-one-quarter inches wide, and as long as the lumber pile is wide. It is important that stickers are uniform in thickness and kept dry. Stickers are placed perpendicular to the boards’ length, every 12 to 18 inches along the pile’s length. The stickers are placed directly above the stickers in the lower layers. If the lumber is of varying lengths, shorter boards are staggered by alternating them from one end to the other with the longest pieces always on the outside edges. The ends of every board should be supported with a sticker. Stickers hold the lumber flat, preventing warp, while also allowing air to circulate through the pile and dry the lumber. While the lumber is being stacked or prior to loading the kiln with pre-stacked lumber, several sample boards must be cut (see Appendix C: Procedures for Cutting and Using Sample Boards). Periodically checking these sample boards will allow you to determine the moisture content of the lumber in the kiln and to observe possible drying defects. A combination of the rapid moisture loss driven by the dehumidifier and the high air speeds driven by the four fan units can overwhelm the novice dry kiln operator. Limiting the run time of the dehumidifier and reducing the fan operation to two fans will make the kiln more forgiving for the novice operator. Basic Operation of a Lumber Dry Kiln WARNING Although lumber drying is a very simple process, it requires constant monitoring and detailed record keeping to produce a quality product. Expensive grade lumber can quickly be destroyed beyond use by extensive drying defects (e.g., checking, honeycomb, end split, etc.). We strongly recommend that you read additional kiln operation materials such as the Dry Kiln Operator’s Manual listed at the end of this publication. In addition, several kiln operator training courses are offered in the eastern, western, and central United States. 4PDF Image | DH Drying for Small Woodworking Firms and Hobbyists
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