Cheap moisture meters - Accuracy

[Treeeeee]

Hello,

I've got a cheap Stihl replica moisture meter for nothing more than a rough guide.

With a few slabs that I know have been kiln dried and then stored in a workshop I'm getting readings of around 14/15%. (slabs up to 65mm thick)

With some interior furniture that again has been kiln dried and in position for months, I'm getting readings of around 10/11% (slabs up to 45mm thick)

With a block of elm I know was cut around 3 weeks ago I'm getting readings of 45/50% + (350mm cube)

However, with some walnut that was cut around 3 months ago I'm getting readings of 18/20% all over with pushing the 'prongs' in deep. (75mm thick) I should've weighed it but unfortunately I didn't.

I am aware that the walnut can't be that dry yet, but it does have me wondering how useful/ accurate a cheap moisture meter is?

It's obviously picking up a variance in moisture/ resistance if thats how they measure.

Are the readings accurate at all?

Thanks for any help




Thanks

 

[porker]

I only use a cheap moisture meter sometimes on logs for burning. Anything where the surface has been exposed is potentially going to be drier than it is deeper in the wood. With a log I would split it and measure the fresh split face but you aren't going to want to do that with a nice piece of walnut. Those readings (based on my experience with logs for burning) look about right. The cheap meters are as you say just resistance meters and can't be calibrated to the correct species, humidity etc. I think they are OK for comparative measurements but for an absolute measurement I would say mine is probably at least +/- 5%. I think you would have to spend a lot more to get anything accurate.

 

[Treeeeee]

Thanks for the response, what would be an average difference of an outer face and the centre of a split log?

Completely agree with having to spend a lot more to get an accurate measurement. Not something I want to do at the moment.

Thanks

 

[CHJ]

I have two different brand cheap meters, they both agree with each other over a range of levels.
If I place the prongs across (don't stick them in it hurts) an index finger to check they're working they usually read between 18 & 20%.

They both give the same readings using the resistive test pieces supplied with one of the units.

Cut down logs can vary considerably, was the Walnut tree still 'alive' or was it harvested because it was dead or dying?

Wood logs and billets in my storage areas usually settle at 12- 15 %, this can take anywhere between 12 & 48 months.

I don't usually work it if I see more than 5% between inner and outer on a test cut, but will slab it at this level to speed up drying if appropriate.

But even with this sort of gradient, once worked, (turning) the reading can go down below 10% (cutting/sanding heat/centrifugal forces?) but can go back up again dependant upon room location.

The meters are certainly good enough for my needs and tolerance seems to be well within the seasonable differences exhibited by finished pieces in the house.

 

[Treeeeee]

Thanks for your help.

It was actually dead standing, here is the base of it -



Just seems strange to be reading 18% after around 3 months of being stickered, although the moisture meter seems to be reading at what should be expected of everything else.

I'm tempted to cut the ends of the slab (which would have been cut anyways) and take a reading from there.

Thanks

 

[novocaine]

depending where your piece is from on that tree it could be in the 18% margin, it looks to be long dead, so the wood has been drying out for a long time (not in perfect conditions but all the same), did you meter it before you put it in stick?

 

[acewoodturner]

A mate and I milled up an elm a few years ago which had been felled by the council about 3 months previously. As we are both furniture makers, we both have different but expensive and accurate moisture meters. The planks were about 18% mc and dry enough to put straight into our workshops. The elm had been standing dead for about 2 years or so prior to felling and had been killed by dutch elm disease. It was also about 3 to 4' in dia and had some cracking burrs on it. We planked it on the 1st May (cant remember which year but it must have been about 10 years ago) as I remember getting home about half ten at night to a not very happy wife as it was our wedding anniversary!

Mike

 

[Treeeeee]

depending where your piece is from on that tree it could be in the 18% margin, it looks to be long dead, so the wood has been drying out for a long time (not in perfect conditions but all the same), did you meter it before you put it in stick?

I'm fairly sure I bought the moisture meter after the walnut and did do some readings, however I can't for the life of me remember what they were.

They may have been around 35% but I can't be sure at all.

Thanks

 

[Treeeeee]

A mate and I milled up an elm a few years ago which had been felled by the council about 3 months previously. As we are both furniture makers, we both have different but expensive and accurate moisture meters. The planks were about 18% mc and dry enough to put straight into our workshops. The elm had been standing dead for about 2 years or so prior to felling and had been killed by dutch elm disease. It was also about 3 to 4' in dia and had some cracking burrs on it. We planked it on the 1st May (cant remember which year but it must have been about 10 years ago) as I remember getting home about half ten at night to a not very happy wife as it was our wedding anniversary!

Mike

Thanks a lot for that! A lot of reading I have been doing was suggesting that standing trees do not really reduce in moisture content.

However if the base of a tree looks like the above, I can't see how it can retain moisture for years. I'm sure I'm wrong thought!

thanks

 

[acewoodturner]

It was certainly the driest tree I have milled out of the hundred or so we have done over the years. As opposed to that I cut the top of a windblown sycamore which was about 15" in dia which the tree was lying down an embankment. I cut the crown off in one piece and was amazed just how much sap started flowing for several hours. I could have filled a 5L container in about 20 minutes. It wasn't rainwater as the tree was solid and had no cavities in the trunk either.

 

[Treeeeee]

Wow, that sounds amazing!

Is there anything I can do to test it?

Make a cut off the end and measure the centre?

Cheers

 

[Treeeeee]

It definitely just the surface thats dry.

Surface reads 17 - 18%

Pushing the prongs into full depth gets to about 24% in some places.

So I chiselled a small square out of one of the ends and took a reading which was 50% +

Looks like it'll be staying outside.

Cheers

 

[hawkeyefxr]

I have has a moisture meter for quite a few years and while i have no idea as to it'd accuracy it's still a good gauge. If you have some wood that been in the house for a few years take a sample reading from is and compare it with a piece of wood from you shed then another piece from say the garden.

 

[andersonec]

The average moisture meter will only give a reading of what's near the surface, professional meters have to hammered in to the timber approx 20 mm.

Andy

 

[Treeeeee]

I have has a moisture meter for quite a few years and while i have no idea as to it'd accuracy it's still a good gauge. If you have some wood that been in the house for a few years take a sample reading from is and compare it with a piece of wood from you shed then another piece from say the garden.

Thanks for the response!

I've taken quite a few sample readings and comparatively theres a big difference showing between green and interior dried.

However, the walnut was cut around 3 months ago but was showing around 20% until I chiseled a small amount from the end and that revealed internally it was still very moist.

Thanks for your advice!

 

[Treeeeee]

The average moisture meter will only give a reading of what's near the surface, professional meters have to hammered in to the timber approx 20 mm.

Andy

Absolutely, the same as my findings.

Surface was fairly dry, however when pushing the prongs deep it certainly rose.

Thanks a lot