Does anyone here use moisture meters to test there timbers before working on them? If so, what brands do you recommend, and what would you consider a good moisture content for stable wood?

Thanks,

Tim

Lots of people will throw out numbers for what they consider good moisture levels, but in the end stable moisture is reliant on your local absolute humidity levels, absolute humidity being how much water is in a certain volume of air rather than how much water is in that air compared to how much it can hold at that temperature (which is relative humidity)

The stable moisture level will be significantly lower in Arizona than Indiana.

Here in humid Indiana, we will generally consider things to stabilize around 12 to 15% moisture content. I have heard that in some places that level can be as low as 6%.

Now from here on lets be careful lest we turn this into a green framing v. seasoned framing debate... (I am on the green side myself) But suffice it to say moisture level is only a concern to some. There are those who use carefully dried timbers in their frames, and there are those who put it all together green. If you are letting your own timbers air dry, then you need a moisture meter. If you are doing with green or Kiln Dried wood, then you don't really need one, unless you are operating your own kiln of course.

Tim,

That's a good question. We've looked at buying a MM several times and still haven't for some reason. I'd be curious to hear from those who have and use them for timbers -- I couldn't find anyone with directly relevant experience when I was looking.

The reason we would get one is if the specifications on a high end job called for the timber to be below a certain number -- 19% is the one I see in specs most often. In that case, it would be helpful to be able to verify that my supplier is meeting spec and that my product after fabrication is meeting spec.

DL is right that equilibrium moisture content varies regionally. Here in the humid southeastern US, I consider 12% to be EQMC.

One thing to note is that there are two types of moisture in wood -- bound water and free water. the free water is the water that exists outside of the wood cells. The free water is the first to evaproate. For most species of wood, once the free water is gone and all that is left is bound water you are at around 30%MC. It's important to note that this is the point at which shrinkage begins -- when the cells begin losing the bound water. It continues until equilibrium MC, which is dependent not on relative humidity but absolute humidity levels as DL said.

(As an aside and not to encourage a green vs dry debate, I believe there is ample historic evidence that many high-end buildings were built with dry wood. I'm talking churches and great halls, not average residential buildings. In our work the same is true -- high spec/high end projects usually use the more expensive dry material while "normal" jobs use green.)

Lots of specs written for '19%' - but with a standard meter you'll only see that to about 1" of depth. What happens beyond that is anyone's guess.

I'm not sure how useful it would be beyond 'That looks drier than that timber'... especially working in green material, or even conventionally kiln dried material - where you can only get the timber (unless it is narrow / small) to give up a portion of its moisture on the outside.

The RF folks out west have a pretty sophisticated method of seeing inside timbers:

http://www.fraserwoodindustries.com/index.php?action=products.heartdry

still wanting not to go into this debate, I think Gabel brings out a good point. High end projects might require, and be able to afford, kiln dried wood.
In the old days in Continental Europe at least (can't speak for England, Ken may have to chime in on that) some timbers were allowed to season for a time. This was done either for high end jobs, or for a few vital timbers on other jobs where shrinkage might be catastrophic. The method of drying was not to use a kiln, but rather was to store hewn timbers in some out of the way location for several years. This would not stop checking, but it would keep the timbers from moving in situ.

It is also important to note 1 thing regarding green timbers.
In the old days, the trees were carefully picked and cut at the exact right moment if they were to be used without seasoning. In Germany this right time is between the middle of November and I think the New Moon around the end of January, first of February. Although it could be the full moon I am not quite sure. The reason for this being that during this time period the moisture content of the wood is at its lowest (the moon cycle affects when the sap comes back up into the tree)

How about weighing the timber and comparing it to a known dry weight?

I am starting to stock pile brace stock for future use. And more importantly, naturally curved stock would be nice to select from. As I walk around my mill yard I can point out the dryer piles, they are grayer.

While on the topic of dry timber, I recently uncovered a pile of timber, it had a tarp over it, there was more ice on the covered timber than an uncovered pile. I just swept the dry snow off the uncovered pile, I will be scrapping ice off the covered timbers. I suspect moisture from the ground could not escape the tarp and froze on the timber, and or some of that free moisture coming out of the timber got stuck under the tarp. It was not covered all the way to the ground, either.

Hi everyone

Great topic and quite controversial I must say with everyone having a little different slant

As one of the old timers in this group I thoroughly enjoy the back and forth ideas and pointers.

At UCV we had quite a historical maintenance department headed up by one of the best architects in Canada, what he demanded for special timbers (ones that would be used say inside a mill or heated home) needed to be processed either hewn or sawn depending on the situation and stored in open sheds for a period of 3 years, well stickered, a period longer than this required a repiling and realigning the spacers to allow the timbers or sawn lumber to recover at the sticker points, and prevent points of rot to happen.

Even after this length of time the timber is dry only down to the relative humidity of the surrounding air. The longer the storage time the deeper into the timber the stability penetrates

I thoroughly agree builders from time gone by had a better choice and control of the timbers quality, by the fact that most timbers were harvested during the cold dry part of the year and gave the curing process a real kick at the can. The same can be saidof firewood white ash harvested in the winter can be burned immediately

NH

For NH,

Beechwood fires are bright and clear
If the logs are kept a year
Chestnut's only good they say
If for long it's laid away
Birch and fir logs burn too fast
Blaze up bright and do not last
Elm wood burns like churchyard mould
Even the very flames are cold
Poplar gives a bitter smoke
Fills your eyes and makes you choke
Apple wood will scent your room
With an incense like perfume
Oak and maple if dry and old Keep away the winter Cold
But ash wet and ash dry
A king shall warm his slippers by

An old english saying

hi everyone tonight

Hi timbeal and others looking in

well timbeal you are a poet and don't know it for sure


Nearly everything is true in that recital except the line about elm--I grew up burning elm it was the backstay of our wood supply for the winter-we had lots and boy would it burn andheat well,sure nothing wrong with elm in my books better substitute another type of wood

It really wasn't a good lumbering wood other than for timbers, and joists were ungodly strength was needed due to bending and loading


NH

Hi All,
Sorry about the new username, this is Don P. I apparently broke off my key in the lock awhile ago. Anyway...

I use an older Delmhorst pin type meter with 3" insulated pins on their largest slide hammer. These meters are basically measuring resistance between the pins, in billionths of an ohm from what I understand, and convert that to a moisture content. an insulated pin reads only at the tips, so as I drive them in I'm reading the mc at the depth the pins are at. As I drive in I'm reading the "moisture gradient" from shell to core.

A high gradient is telling me that the shell is drying and shrinking around a still green and swollen core, great checking potential. A uniform reading tells me the wood is probably approaching emc... which is not a fixed moisture content anywhere. It averages about 12% in an outdoor (unheated) under shelter location here, in the VA Blue Ridge.

Gabel is pretty much right on in his comments, free moisture is the moisture within the cell lumen, bound moisture is the moisture that is chemically wrapped up with the cellulose within the cell wall itself. The point where the free moisture has left the cell cavity but has not yet begun to leave the cell wall is called the "fiber saturation point". As the bound moisture leaves the spaces within and between the cell wall fibers shrinkage begins, mechanical properties change.

A couple of interesting things happen right there, fungi need free water, as the wood dries below FSP fungi lose interest. FSP is a cell by cell point not an entire stick of wood point, remember the gradient above, the shell can be well below the FSP while the core is well above it. Drying commodity lumber down below the FSP is one way of making sure it won't decay while dead piled in a lumberyard... if they store it properly. Nowhere in the US is 19% emc though, the wood still has drying and shrinking to do from that point down to EMC. As the fibers dry they become tougher and stronger, carpenter ants cannot chew through them easily, they go looking for saturated wood.

The moisture content of a living tree does not drop in winter and in fact is sometimes higher in hardwoods where the leaves are not there to cause transpirational losses. Evergreens are evergreen because they are still growing and photosynthesizing through the winter... whenever the temperature allows the sap to flow. Winter cutting does give the wood the opportunity to dry with low moisture gradient through a period when fungi are halted by the cold, hopefully by the following spring the wood is below FSP and you can stay bright and fungi free, so there is good reason to winter cut but it isn't because sap goes down, it doesn't. Cells that embolize die, a tree cannot re-establish a broken water column.

This is a shot of my meter in some supposedly 17% cypress logs that were sold by a crook.

The top left part of the pic shows a dry shell... below fiber saturation point and a wet core, above fsp. When you can see the moisture you are seeing the free water in the cell lumen. When it looks dry you can say that it is below FSP for that species, that is all you can say at that point, but that is no small amount of knowledge right there.


If you know the temperature and relative humidity you can determine the equilibrium moisture content. The thermometer/hygrometer is giving that part of the equation here. If you look up the emc you'll see the meter is pretty much agreeing with those conditions. It's always a moving target, the temp and rh would have been a bit different a few hours before that and were surely a little different a few hours later so the emc will be within a % or so of that reading.

Timbeal had the most accurate suggestion, meters are ok but weight is the most accurate way to determine moisture content.