Measuring Moisture

Issues concerning moisture are constantly arising in the timber industry and of such importance it is good practice if wood pallet and packaging manufacturers build up a knowledge of the effects of moisture. Popular robust instruments can be viewed on 

If a  customer has specified kiln dried pallets the manufacturer should at least keep a record of what moisture content newly kilned timber arrives at goods-inwards, and in due course at what moisture level pallet stock destined for customers leaves the factory gate. It takes less than a minute to monitor and record a selection after production and by taking half a dozen readings across a batch and routinely recording these, it can potentially save or explain customer complaints since you will have early warning of over-high moisture levels .

Wood moisture meter being used with
a checkbox calibration device

Moisture meter instruments. To record the moisture content of timber it is necessary to have a moisture meter handy on site in order to take readings and keep records. We are frequently asked to help manufacturers when a customer has problems with pallets which are associated with high moisture. More often than not the manufacturer has no idea what the level of moisture was on arrival at the customer's site. That immediately means at the other end of a phone we are restricted in what we can do to help solve the problem.

A moisture meter should be a working tool, not locked in a cupboard. A pocket model is cheap and even if the meter gets dropped or left out in the rain then if you have a checkbox calibration device (shown in the illustration - a patent taken out by TRADA) it takes only 15 seconds to see if the moisture meter is still working and accurate. Possession (and periodic use) of a calibrated checkbox will ensure all moisture meters on site are usable.

The most accurate type of moisture meter is the resistance (or conductivity) type moisture meter with 2 pins which are pushed a few millimeters into the wood. This type is covered by BS EN 13183:2, is specially designed for use in sawn wood and if bought from a reliable maker and used with a checkbox is very accurate.  Moisture measurements can be taken using the integral pin electrodes shown in the illustration, or using the meter in combination with a hand held moisture probe on a short length of cable. If you use dry or kilned timber in production and your ISO 9000 or EPAL assessor assesses that part of your system, then a company not owning a regularly calibrated moisture meter would be a recordable non-compliance.

Hygrometer instruments. A hygrometer measures moisture-in-air as opposed to a moisture meter which measures moisture-in-wood. If a wood packaging customer has problems of product corrosion, moulds or sapstain and you suspect it is caused by damp air storage conditions then a pocket hygrometer is used, which reads in percentage relative humidity (%RH). However, beware, because as opposed to a moisture meter which registers in 2 or 3 seconds, some hygrometer instruments, even from well known makers can take 5 minutes to settle to a reading and no-one has that sort of time to spare since several readings are needed for solving any problem. Knowing the reading-response time of a pocket hygrometer before you purchase is critical for these instruments to be of any real use.

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PDF42a Moisture Protection in export packing. (PDF 32kb)
PDF77c Traceable wood moisture calibration - background. (PDF 55kb)
PDF77e Introduction to wood moisture meters. (PDF 69kb)
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