Moisture meter and oil content of wood?

[ndp_2010]

Hi, I have a pinless moisture meter and was wondering if anyone knew whether very oily woods are going to affect moisture content readings. (ive had a look at google but cant really find much of an answer). I do know pinless meters are using a kind of electric field to determine the amount of water in wood and it might just be specific to the actual water molecule but I am not sure.

Ive got a few blocks of oily woods (olive, snakewood) that are showing fairly high moisture content (even though a small block of the oilve has been seasoning inside for a good 10 months) so that leads me to the original question. :D Anyones experience would be welcome. Currently using Wagner MMC220.

[BobL]

The values shown on the readouts for all moisture meters are for a specific timber e.g. Douglas fir.
If you want accuracy for other timbers a correction has to be applied based on something like correction chart or a correction module.
Some meters come with some correction charts and charts for aussie timbers are available for some meters, for a price.
If you cannot find a chart for a certain timber you have to make your own by performing absolute measurements across a range of MCs using a balance and an oven.

FWIW even small pieces of Olive take for ever to dry out at room temperature, certainly 10 months is nothing even for a small block.

[rustynail]

The word "block" makes me think these pieces are in excess of an inch thick. If so, they are going to take some time to dry. Rule of thumb 12months for each inch of thickness.

[ndp_2010]

Thanks for the info. Yes the wood is about 35mm thick x 45 wide.

I wonder if the species chart is utilising oil content as a factor too? Density is a big player in the Reading I know.

Maybe Iwill soak some wood in some oil and check if the meter reads significantly different and it might help shed some light on this =)

Thanks everyone for the reply

[BobL]

Soaking the wood in oil won't be a valid test. If the wood is even partially dry the cellar structure of the timber will have been compromised and what oil "soaks in" or "does not soak in" will be different to what the wood does naturally.


I wonder if the species chart is utilising oil content as a factor too? Density is a big player in the Reading I know.


The species chart for a MC meter is determined by measuring the MC of a piece of wood directly by weighing it and comparing that weight to the weight of the same piece of wood after it has been in an oven for some time (zero MC weight).
This process does not take into account what is volatilised by the drying process, so whether its oil or water is not taken into account
Density effects the readings obtained from dielectric meters but does not come into the MC determination by the oven drying method.

See http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0007/389689/Methods-of-Determining-the-Moisture-Content-of-Wood.pdf


Oven-drying will over-estimate the true moisture content if the wood contains significant amounts ofvolatile material that evaporates with the moisture during oven-drying. This can occur in speciescontaining natural volatile oils or resins, but the effect is not often large enough to be important, and isusually ignored in practice.

[Yanis]

The contact-less meters use differing technologies so the answer will actually vary. Some use inductance and some capacitance and some a combination. The former uses the pemitivity and the latter permability of the wood which is another way of saying that the chemical composition of the wood, including water, resins and oils will impact the ability of the material to enhance the inductance/capacitance of the wood. The biggest effect is the water since it has the greatest electromagnetic reaction to the signal used by the meter.

The second biggest factor is the density of the wood which is why the meter has a compensation factor that is directly related to the wood's density. You can calculate the correction factor by taking a sample of the wood and calculating its density. However this only varies the reading by a few percent.

The oil will most likely alter the accuracy but I suspect that it would only vary by a few fractions of a percent. Probably not enough to consider.

As an experiment I have a small bottle of olive oil and the bottle itself reads 5% and the jar with oil reads 8.5% so the oil itself alters the reading by 3.5%. So if the wood was oily then that quantity of oil would barely alter the reading. But yes, it would read high but not by much, less than a percent I would expect.

John

[ndp_2010]

thanks for the answers definitely something to think about.
Seems to be a tricky subject to get the moisture content of wood and at the moment I am just using it as a rough guide and also for before /after tests on the same piece. Ill have to do some oven drying to see the full extent of the dryness I can get and the reading I get.

cheers