Measuring Moisture

Many years ago I wrote about the wood I worked with in Texas called mesquite. Mesquite can be mistaken for a mahogany-type wood because of its red-to-brown colour, but touch it, lift it and work it with hand tools and you can feel the massive difference. Back then, in the article I wrote, I resaturated different species of North American hardwoods to prove a point. Mesquite is most likely one of if not the most stable wood in the world. It makes the best cutting boards ever and believe it or not (I don’t care) a single-piece mesquite cutting board will not crack or warp no matter how many times you leave it in dishwater and otherwise mistreat it. Try that with any other hardwood from North America!

Anyway, back on track! Back then 20 years ago, I took 152mm (6″) wide sections of wood and soaked them for 24 hours in a bucket of water. Previously all dried down to 5% MC levels, maple, oak, cherry, walnut, together with others, all expanded to between 10mm (3/8″) to 12.7mm (1/2″). Mesquite only expanded 2mm max (1/16″). I have done things with mesquite that you cannot do with any other wood. A piecrust table for instance. In solid wood, the outer circumference edge will expand a hundred times more than the inner areas. You’ll end up with cracks and separation of the components, hence they are made with a substrate and veneered with piecrust veneers only.

The two on the left look surprisingly alike . . . That is because they are made in the same factory.

Currently, I have been experimenting with how and what changes take place in black cherry for my rocking chair. I am using four different moisture meters supposedly by four different manufacturers to trial them for efficacy, so if you see me using different meters, that is why.

That said, I suspect that inside the plastic outers the innards are all Chinese made by the same maker no matter which name is stretched over the outside or which country they are supposedly made or assembled in. Who knows anymore?

I had bought in some 4/4, 5/4, 8/4 and 9/4 boards of cherry which all checked in at around 10-11% MC three months ago. I have made two cherry rockers from that wood and on one of the chairs, the seat is allowed to ‘float’ atop the frame so no problems except a slightly bigger gap here and there. No more than expected.

Wanting greater control or to compensate for such movement I decided to know more. I have done this on other pieces I have made. I like it. In 36 hours my tests on my cherry wood showed as follows: I increased the moisture in sample ‘C’ from 5.2 on up to total resaturation of 28% by immersion. I dried sample ‘A’ down to 0% using radiated heat. The text shows details. Sample ‘B’ remained static in the garage workshop with no interference. Interestingly, sample ‘C’ went back down to 12% in 36 hours. Sample ‘A’ increased in width by 1mm with no weight change. By testing samples this way I can better gauge what my wood will actually do in the zone. It’s not the type of thing you can read in a book. I want facts at the bench. And if I want to I can thus minimise risk to achieve what might not normally be achievable if I just winged it (and I do wing it too). I can now calculate how much cherry will shrink or expand in a permanent domestic situation. Something that varies markedly according to different households.

In the case of my rocking chair, I am trying to get guaranteed results for my audience should they decide to build one for their family use. I have made the same rocking chair in oak recently. Oak is usually quite forgiving with regards to expansion and contraction because it is so very ring-porous. It has stretch and elasticity due to the large open pores at each level between growth rings. In other words, it’s ‘spongier’ than cherry is. Some woods do not. Cherry and oak are different. And you can see the lighter band of ring-porous wood on the outer of each band here (the bands go top to bottom). This is the band that gives stretchability and compression in oak.

In cherry, you will see porosity is much more evenly and densely distributed throughout the wood in much smaller pores. This is termed diffuse-porous wood. My non-scientific testing gives me to understand that cherry is less stretchable and compressible than the oak I have is.

I think that this is interesting enough to write about here but it is much more mind blowing in the zone at the bench and it doesn’t take long to do either.

24 Comments

  1. In summary, if I understand this correctly: if you live in an area with seasonal variation in humidity, you’d be best off with mesquite then oak then cherry. Outside of the US that probably means oak over cherry. Thank you.

  2. I recall a book, “Understanding Wood” by Hoadly, that went into great detail. I could be conflating something I took away from it with another source but something that stayed with me is that if you construct a piece solidly enough in violation of the expansion and contraction it will hold together because the wood gives up after a while. I’ve found this to be true in certain antiques I have observed. The old craftsmen sometimes went against the grain, so to speak, and got away with it. That might have something to do with the fact that they used lumber from old growth as well.

  3. I’m constantly thinking about wood movement, here in New England my house humidity swings from 17% in the winter to around 75% in the summer. I’ve learned the hard way to allow for wood movement. With all due respect I don’t think you can overbuild a piece to overcome wood movement. I’ve seen 4” fireplace mantels warp and split when constrained with steel bolts.
    It seems like everything is made in China nowadays! What I don’t understand is how they can be the least expensive when they are halfway around the globe from us.

    1. Yes, I might agree, but often the builder’s way is to bulldoze. I doubt very much that the mantle was ever measured for moisture levels. They just picked up a section of oak, likely cut a few weeks earlier, dare I say, and bolted it in. Such mass with steel bolts would never have constrained such wood mass. I could have told them what they should’ve known. On the other hand, moist woodworkers do not experiment or even test their wood. Big mistake. The swings you speak of are interesting too. I experienced this in Texas where I made pieces intended for Houston and then for West Texas showing the two extremist of extremes. I had to face some sharp and costly realities there. In my chair I have built in a backstop to ensure there are no pitfalls. In your case, you can of course do as I do and add or remove humidity if you feel to. I dehumidify mostly. Remember the 24″ deep cherry dresser we made few years ago? Well, it is in my bedroom and shows zero movement even around the dovetails. This is impressive. I did see a shaker style one we made ship to New England from Texas two decades ago and we had no issues with it.

    2. Until recently the transport costs for containers from china were so cheap that many importers did not find it worth making the calculations to overall selling prices! It would seem unlikely that the UK shall ever be able to build a manufacturing base after we have lost so much trained skilled labour or even will to work in manufacturing. Globalisation seems like a very bad way to describe loss of global manufacturing…

  4. I live outside of Amarillo, TX up in the panhandle and we stay pretty dry most of the time. I have a shaker style jelly cabinet that I made nearly 40 years ago. I have never had enough moisture change in the house to really make it move to where the door didn’t easily open.

    I wish I could get mesquite in the sizes that Paul did but it is a very expensive wood in the panhandle when you get wider boards. A lot of the larger mesquite around here gets used for mantles. The mesquite that grows around here usually isn’t much bigger than a bush. When I worked at a natural gas plant mesquite was more of a pest than anything else. Usually most of the newer employees would wind up with a bad cut in their arms from the mesquite thorns when they would drive the back roads with the window down and their arms resting on the door and their fore ams and elbows hanging outside of the truck.

  5. Paul,

    A bit off topic, but how do you sharpen your wood turning tools? I don’t think you’ve ever gone into it.

    1. On a grinder, and there is no one-way-fits-all. I don’t really get into woodturning except for the needs in some aspects of furniture making and even there I use it minimally.

  6. Several years ago before I knew about Paul I visited my son in Arizona. I was just starting to acquire a few hand tools and thought it would be fun to see how maequite worked, so I brought home a few short logs of it. When I tried to make anything from it a split it the wood would ruin the project. The splits didn’t appear on the surface, but as I got closer to the desired dimension they seemed to show up. I did manage to salvage small pieces of the log which I turned it into one of Paul’s dovetail markers which I still have. Are we talking two different species of mesquite? Just curious. The dovetail marker finished off quite nice, but I haven’t been too crazy about making the trip to Arizona to get more of it. In fairness I didn’t buy the mesquite from a store but was some my son had stacked in his yard, but it was what they call mesquite.

    1. Hi, Dave. I live in the greater Phoenix area and have seen mesquite turn up at a local, beautifully stocked wood seller, Woodworkers Source. Those boards are usually not very wide and yes they are usually full of twists, turns, cracks, checks, and inclusions of bark/knots. Still pretty, but definitely kinda rough looking. Having seen trees around this Valley for years now, I can say they don’t seem to usually grow big trunks. The wild ones are big multi-trunk “bushes” more than trees in the “oak” sense. The landscape ones are pruned to one trunk, but usually seem to die or get taken out by wind before the trunk hits a foot or a little more across. Whether this local mesquite is 100% the same as in TX, I can’t say. Arborists and landscapers say we here have had South American mesquite brought in for landscaping for decades, and so there has been hybridization between them and the native mesquite varieties (whose seed pods the natives used to mill for flour). I sprang for a smallish board that is pretty clear but have yet to make something with it. Waiting for just the right small project that if will shine in.

    2. Some realities about mesquite:
      Yes, mesquite is prone to wind checks which occur during growth and when you slab the mesquite they are there and you can do nothing about it. You will not know that they are there until you cut and slab it. I guarantee that it will not split once it is slabbed and dried down in a controlled way and once it is slabbed you will have no problems with it. It is not necessarily straight-grained in the same way as any other wood and so planing with hand planes requires some dexterity.

  7. Paul,
    Harvey Boulanger here. I live in North Central Texas. I am a turner, carver and all round wood guy.
    The land is being cleared at breakneck speed to receive all the transplant fleeing from tax burdened states.
    Mesquite, cedar elm, and other hard woods are being burned.
    It is an opportunity for me to harvest Mesquite. I do enjoy working with it and find it the most stable of all native Texas woods.

  8. What I am missing is:
    how to buy wood in a lumberyard?
    { what to be looking for?
    what to avoid?
    what to completely exclude?
    how not to be cheated? …}
    This would be a nice addition to your wonderful skill building videos.

    1. When restrictions end I would like to do this thoroughly for everyone. Thanks for the nudge.

  9. Try Australia for variations in climate and timber/ lumber moisture change.One hard environment on any wood.The preciseness required to successfully dry/ season some of our wood is really critical.Some wood species really need to be only used in the region’s in which they naturally grow and then it’s no guarantee it won’t check, warp or split later on.Some species do fare better but one finds these to be recycled old growth wood and generally imported Baltic pines Douglas fir and some Asian rainforest species.Wood actually will acclimatise to its environment and aquire a constant moisture content for a particular region.If your wood arrives from Tropical north Queensland and ends up in a semi arid dry place like Bourke you need it to acclimatise for 2 or 3 maybe4 weeks.One should not balk at using Marine UV stabilised finishes as some times it is the only way to preserve a finish on wood here in Australia From -0 c up to 48 c temps here so not user friendly for even local species .
    Keep on chipping on
    Richie

  10. Paul,
    would kiln versus air drying on a rick make a difference in how this would work out. I know that traditionally ship carvers needed to use air-dried over kiln dried due to the unwanted later expansion of kiln dries on a boat. Also, users of tonewoods claim that there is a notable difference in the wood’s tonal quality based on how they were dried.

    1. There is no doubt that air-dried gives greater stability but we shouldn’t decry all kiln-dried wood, that depends on who’s drying it and how. Slower is generally better so even when you use a kiln you can step off the conveyor belt and take a little longer over the process. I have used solar powered kilns with very good results. You can clip off a year or two by using a more natural approach. I am not sure about tonewoods but I think it does make sense. Why rush what doesn’t take that long in the first place. Keeping wood in your workplace takes much less time than you think it would. With wood so thin it takes a lot less. I have tried the wood I had in my house and the wood is much higher in moisture levels than at my garage workshop. Life is a wet thing.Showers and baths and cooking all produce list of atmospheric moisture that gets sucked into dried wood.

  11. Hi Paul, I have the meter second from the right in the photo. I’m fairly inexperienced using it so I wanted to ask your opinion on it. Did you think it was accurate/reliable/consistent? Thank you.

    1. This is the one I have been most disappointed with to date. If you are still within your warranty I would return it and get any of the others. You can see two cases are different colours here but they are identical and they do give accurately the same readouts as does the Stanley as it corroborates as best you can gauge. For the most accurate you might consider the high-end ones but that’s not altogether necessary as weight and weighing will tell you much more as will width and thickness measuring. I rely on this mostly but the meter gives me a starting point.

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