28
To measure moisture content on a daily basis, it
is best to use sample boards. Moisture meters are
not accurate enough for most hardwood dry kiln
operations when the wood is above 30% MC and there
is a need to keep a close watch on the drying rate.
In Oak, for example, all checks and honeycombing
occur when the wood is drying from green down to
40% MC, so that is when the drying rate needs to be
closely controlled.
• To estimate the MC of the load in the chamber, so
that kiln conditions can be regulated according to
drying schedules.
• To measure the drying rate, which allows control of
drying quality.
• To check on any degrade development.
• To check on nal MC and drying stresses.
• To develop a MC vs. time curve.
• To study variations in drying within the kiln.
• To monitor changes in MC after drying (during
storage and shipping) Note: It is a good idea to keep
sample boards with dried lumber so that they can be
used to track moisture content changes in storage.
Step 1: Select sample boards. Keep in mind that they
need to represent a “sample” of the lumber in the kiln.
Do not select junk boards, and select both the slowest
and the fastest drying boards of the load. Generally,
you want six sample boards.
Step 2: Cut 30” samples, at least 12” from the ends
of each of the sample boards. Avoid having knots,
splinters or bark in the sample.
Step 3: Number the samples you cut.
Step 4: Cut two 1” sections o each end of the samples,
and mark them with the number of the board they
came from.
Example: the two sections that came from sample
board 3 would be labeled 3A and 3B.
Step 5: Apply end coat the now 28” sample boards.
This assures that the sample board will dry as though
it were a larger piece of lumber.
End coatings are not usually required when lumber is
placed in the kiln directly after being sawn. However
when lumber is air dried prior to kiln drying, end
coating is often helpful in preventing end checks
U.C. Coatings is the major supplier of end coatings.
Contact them for further information:
U.C. Coatings
P.O. Box 1066
Bualo, NY 14215
Telephone: 716-833-9366
Fax: 716-833-0120
Step 6: Weigh the 28” sample boards. An accuracy
of .025 pounds or 1 gram is recommended. Record
these values.
Step 7: Put the 28” sample boards in the lumber stacks
in places where they can be reached and will dry at
the same rate as the lumber. Do not place the sample
boards where they will receive more air ow than the
rest of the lumber.
Step 8: Take the “green weight” by weighing all the 1”
sections, to 0.1 gram accuracy is suggested. Record
these values.
Step 9: Oven dry the 1” sections using one of the two
methods below.
Microwave with carousel tray: Put sections on a paper
towel on the tray. Use low power (to avoid smoking)
for 20 minutes. Weigh the section, and put back in
the oven for 1 minute. If the section has not lost any
weight, it is oven dry. If still losing water, continue
drying in 5 minute increments until a
Kiln Sample Boards
Uses for Sample Boards
Taking Samples
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