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Appendix B Sample Board Method In order to measure the moisture content of lumber during drying, it is impractical to weigh every board in the kiln. Therefore, the sample board method is used to estimate the moisture content of the lumber in the kiln. This method uses short, carefully chosen sample boards sawn from larger pieces of lumber. These sample boards are weighed periodically and their moisture content’s (MC) are calculated. Sample boards should be chosen to represent all the lumber in the dryer- theslowest drying and the fastest drying. This means cutting sample boards from lumber that represents the driest and wettest, widest and narrowest boards, flatsawn and quartersawn, thickest and thinnest. For the best job of equalizing and conditioning, it is necessary to have the narrowest, driest lumber represented among the sample boards. Changes in kiln controller settings are based on the average of the wettest one-half or one-third of the samples. The precise procedures to prepare sample boards are: 1. Select lumber to be used (see above). 2. Cut a 30-inch sample board and then two I-inch moisture sections from the sample board, avoiding areas near knots and areas closer than 24 inches from the ends of the lumber (fig. B1). 3. Number the sections and the sample board. 4. Immediately weigh the sections (accuracy of about 0.1 gram required). It is important that the sections not lose weight after cutting and before weighing. Record weight on the sections with a marker pen. 5. End coat the sample board to prevent moisture loss through ends. 6. Weigh the sample board (accuracy of about 0.1 pound required) and record the weight on the board. 7. Place the sample board in the lumber stack in a location where it will dry at the same rate as the rest of the lumber in the dryer. 8. Place the sections in an oven at 215 °F. 9. After the sections are dry (no further weight loss is noted)- usually18 to 36 hours, depending on the oven- reweighand obtain the ovendry (OD) weight. 10. Calculate the MC of each section separately and then average the MC of the two sections to obtain the calculated MC of the sample board when it was cut (step 2). Use the formula 11. Calculate the OD weight of the sample board using the average MC from step 10 and weight from step 5: 12. Write the calculated OD weight on the sample board (when it is weighed the next time) so that this number is readily available. 13. Periodically reweigh the sample board to obtain a new, current MC: 14. Occasionally it is necessary to cut new sample boards when the lumber is about 20 percent MC to obtain more accurate MC values (that is, to make a midcourse correction). To do this, cut one new moisture section 6 inches from the end of the sample board. Then follow steps 3 through 13, but use only one section. The “wet weights” in steps 10 and 11 are the weights determined after the sample and new section are sawn. 136 Figure B1 - Method of cutting sample board and moisture sections. (ML87 5493)PDF Image | Dry Kiln Schedules FPL GTR 57
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