Practical/real world rate of re-absorbtion of moisture by kiln dried timber?

[ian maybury]

Pardon the length, but i'm hoping for some fact/experience based input here - based on stuff like meter readings and wood behaviour. In the context of mainstream hardwoods like walnut, oak, maple, beech and the like. So far I've tended to take supplier claims on trust, but after some dodgy experience and conversations (again) today with two separate (local and fairly large) hardwood merchants who either didn't have a clue or were likely not letting on or both thought it might be worth trying to tie the facts down a bit better.

The theory suggests that commercially sold woods like the above are typically kiln dried to 8 - 10% moisture content by commercial producers, and then shipped on in containers and the like to merchants like our local guys who unload it in bundles and stack it in their warehouses which are typically open to the atmosphere. I'm not aware of it being shrink wrapped or anything like that in the way that e.g. solid flooring is. Our climate being fairly damp it then presumably starts to accumulate moisture again - to head back to the 17 - 20% equilibrium moisture content that's apparently fairly typical year round here. The rule of thumb being that it supposedly equilibriates at the rate of about 1 year per inch of thickness.

The above gentlemen both claimed that the most anybody need worry about by way of an increase in moisture content was a couple of percent, and that this would be towards the surface and primarily only the boards to the outside of the bale. That I would need to allow it to settle for a 'day or two' before using it. I asked about how fast they turn it over, and was told that loads would normally go though in a month or two - although my guess is that that's far faster than reality in the present market. That you could easily get a piece that is a year or more old. The commercial makers of kitchens and the like i've spoken to meanwhile seem to just take it as it comes.

The merchants don't claim to consider moisture content to be even a minor issue, although they grudgingly would accept a meter being used on the wood. A surface reading should at least be worst case I guess.

There are a few small producers kiln drying local wood, but it tends to be a bit variable and wild in quality - and the supply irregular in given varieties as there's only two or three, and all are pretty small. (the total market here is tiny)

My personal instinct and longer term plan presumes that getting control of the situation requires installing a small kiln to condition wood before use - or at least moving it into a similar environment to where it will eventually be used for maybe several months - but you wouldn't think so to talk to these guys.

Am I being overly cautious?

Experience suggests maybe not - i bought a large load of supposedly kiln dried 2in beech from a well regarded UK supplier a couple of years ago . This despite promises to the contrary turned out depending on the board and part of it checked to be between about 13% and 16% moisture content - which settled to around 12% in my moderately heated and very dry shop over about a year. What's been used has seemed OK.

Is much more moisture likely to be acceptable given the above and our fairly cool and damp climate? My gut tells me that these guys left to their own devices will simply say what they think is needed to make sales, and after that will without differentiation between boards on the basis of MC simply move them through their operation.

So what's the deal for a small guy that doesn't buy enough to have much clout? Is it just a case of keeping an eye out for fresh deliveries, bringing a meter and refusing boards above say 10/12%. Plus allowing them some time to equilibriate in the shop and after that taking care while working. e.g. process in stages, checking in between.

Does the 1in per year rule in your view stand up in practice for both drying and re-absorbtion of moisture? For both small (few %) and larger moisture changes?

Is there any convenient means of getting a core moisture reading? (damp in the centre is a much bigger deal than just through a thin outer layer given the additional drying time and the risk of warping it entails)

Any key questions/bits of information/good practices a decent timber merchant should have to hand. i.e. how do the good ones do it?

Anything else?

Thanks

ian

[steve joly]

Also very interested to hear some input, sorry I have nothing to contribute but I've been wondering about this also

[Mel Fulks]

I think the most important thing to understand is that kiln drying is a permanent change to wood ,not just a reduction in moisture . Kiln dried wood can re absorb water but will not move as much as air dried . I have an old post about running a test and I still have the wood I used .Both pieces were adjacent in a board ,one piece was KD the other AD.

[Bob Lang]

Ian,

Here in the USA, there are charts that give the average equilibrium moisture content for different areas. The E.M.C. is the key. Kilns here typically dry to 6% or so, and once the wood is out of the kiln the wood begins to take on or lose moisture until it reaches the local E.M.C. In my neighborhood, E.M.C. is generally between 8-10%, dry winter to humid summer. The "one inch per year" thing refers to freshly cut logs (soaking wet) to reach E.M.C.

There isn't anything you (or anyone in the lumber business) can do to change the nature of how wood reacts to it's environment. The best thing I can recommend is to get a meter, and before you go to the lumber yard, check some pieces of wood that have been in your shop a while, they should be at your local E.M.C. The lumber available is what it is. It might be fresh out of the kiln and drier than your shop, or it may have been sitting in a damp yard and wetter than your shop. Either way you ought to wait anywhere between a few days to a few weeks, depending on the difference.

If you don't let new wood reach equilibrium with your shop, it will be moving while you work on it. If the environment in your shop is different from where the finished piece will live, it will be moving until it reaches E.M.C. with its new home.

Bob Lang

[Mel Fulks]

I agree it is good to aclimate when possible,especially with AD wood. The architectural specs that govern most trade work call for KD wood proscribe AD and don't much get into moisture percentages. In commercial work it is common practice to start working wood right away ,regardless of weather or where lumber was stored.

[Joe Hillmann]

In my experience in steam bending kiln dried wood it only take days for the wood to dry back out after steaming it. I don't have any type of moisture meter so my results aren't scientific.

[ian maybury]

Thanks very much guys. For sure the $1M question Mel is how much difference there may be between drying and re-absorbtion. Some digging since posting (the term it seems is 'moisture re-adsorbtion after kiln drying') suggests the following: (it's not a topic that's dealt with in a lot of detail anywhere i could find)

The big guys (e.g. USDA/p. 114 Bruce Hoadley's book - Understanding Wood) seem to suggest that wood regains moisture after kiln drying in a similar manner to that in which it drys in the first place. (the rate is determined by relative humidity, air temperature and air circulation) He reckons that while as you say Mel that it doesn't quite get up to the same moisture content (actually equilibrium moisture content for a given relative humidity - see fig 6.3 p. 113 - the effect is called hysteresis) that kiln drying (as we know) doesn't leave wood in any way irreversibly dry or dimensionally stable.

The 1in per year to equilibrium mositure content rule of thumb doesn't get much credit - it seems it can be quite a long way off depending on the wood species, conditions and shape of the piece.

They don't give much theoretical information about re-absorbtion of moisture, but there's some good info here: http://www.conradlumberco.com/pdfs/ch12_Drying_Control_of_Moisture.pdf - page 12-14 Moisture Control During Transit and Storage - Forest Products Laboratory. 1999. Wood handbook—Wood as an Engineering Material. Gen. Tech. Rep. FPL–GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 463 p.

They say: 'When standard 19-mm (nominal 1-in.) softwood lumber, kiln dried to 8% or less, is piled solid under a good pile roof in a yard in humid weather, average moisture content of a pile can increase at the rate of about 2% per month during the first 45 days. An absorption rate of about 1% per month can then be sustained throughout a humid season. Comparable initial and sustaining absorption rates are about 1% per month in open (roofed) sheds and 0.3% per month in closed sheds. Bales on deck on a ship can pick up as much as 7% during a voyage.

Your weather and/or shop conditions will influence or more to the point stop any further moisture loss or gain or beyond the EMC determined by your %RH - the above is probably worst case seeing as it relates to humid weather.

Which bears out what you say Bob. So it is possible to get very wet timber from a supplier, but it may be a bigger issue over here on the other side of the Atlantic than with your US suppliers who presumably may move more wood sooner after kilning(?).

One basic strategy to avoid this is probably to get it freshly kiln dried - testing with a meter to confirm. I guess unless the wood was stored in exactly the same conditions as your shop/the end use of the wood that there's always going to be a moisture gradient (as in it's wetter or drier near the surface than at the core) - that as you say it needs to be held in the shop for long enough to equilibriate or the result will be movement upon machining/cutting open....

More thoughts anybody?

ian

[michael osadchuk]

I agree with Bob and others that MEC is the key factor to pay attention to in knowing when to use wood, whether kiln or air dried.

Letting new bought kiln or air dried timber 'acclimatize' to the relative humidity in the setting in which you will work iy (and preferably also place the finished piece) by passive storage (no special home made kiln drying efforts) is typically a matter of a week or so rather than months for me. My practical guide is comparison of the moisture content reading of the new stufff vs. wood of same species (or other species corrected for density) which has lived in my workshop/home for years. And I'll use the new stuff once it's within a couple percentage points of moisture content vs existing wood known to be at MEC.
There are also charts/tables in books giving average MEC by region by seasonal relative humidity.

Seasonal MEC shifts for me - just north of Toronto, heated, well insulated basement workshop but with no active control of relative humidity, which varies seasonally on average inside my shop/home from around 35 to 75% - is only about 2 or 3% percentage points of moisture content; example: maple mec ranges 8 to 11% in my situation

The 1" per year for drying guide - R. Bruce Hoadley, author of Understanding Wood, says is unreliable.... in the first edition of his book on page 103 he has a table, titled appropriamate time to air-dry 4/4 lumber to 20% MC and the table gives wide ranges, typically 50 to 200 days or more, for a variety species; he states that the minimum number of days number refers to drying lumber in good drying weather, generally spring and summer... lumber stacked late in this period will ....usually not reach 20% until the next spring.....
... and my experience above with kiln and air dried lumber in my workshop says that the reabsorption of of moisture by such wood is 'not much'.

good luck

michael

[Jeff Duncan]

There's a timely article by Gene Wengert in Cabinetmaker FDM magazine this month. Not sure if you can find it on their website (www.cabinetmakerFDM.com) or not, but it provides a little insight to this question. Actually it more specifically deals with the delay of wood to expand after being dried and then re-absorbing moisture, but is closely tied to your question.

JeffD

[Mel Fulks]

I guess there isn't a way of making wood "irreversibly dry" but kiln dried wood does move LESS than air dried. Test it. Somehow using a moisture meter on wood that is saturated with water seems silly when it has clearly changed dimension much less than an air dried piece also saturated. Some explanations of the difference between AD and KD say that KD removes the moisture in the cells while AD removes moisture between the cells...I don't know. I do know they produce different products.

[John TenEyck]

This might be the article Jeff was referring to: http://www.cabinetmakerfdm.com/8931.html. After I had a couple of bad experiences with "kiln dried" lumber I wised up and bought a moisture meter. I use it with near religious fervor now, not only when buying wood but also to measure how long it takes to come to equilibrium with my shop. I want to know what the MC is of the wood I buy because I don't want to pay KD wood prices if it's really AD wood. But I don't really care if it's 6% or 12%, because I know with almost certainty that it won't be the same as my shop, and that I will have to let it acclimate to my shop for a period of time until it has reached the EMC. Buying and, worse yet, using wood w/o knowing what the MC is or if it's at the EMC of your shop is just asking for trouble - I know this from experience. The rate at which KD wood that has a higher MC than my shop comes to the EMC is surprisingly fast. I recently bought some KD 4/4 maple and poplar that was stored in a closed but unheated building. It measured about 11 - 12% when I bought it. It was down to the 6 - 7% of the other wood in my shop at 35% RH in about 7 - 10 days, at which time I used it w/o any issues.

Moisture meters are pretty cheap compared to just one ruined project.

John

[Mel Fulks]

The samples I referred to were run thru two soakings and dryings about four years ago.Got them out today for another test .Looks like they are now moving at the same rate. That means that I was wrong in saying the difference between KD and AD is permanent. More accurate to say that ,in practical use ,the difference is long lasting to permanent in most uses.I have observed that when KD lumber is checked with moisture meter on arrival and allowed to acclimate ,there is no change in width of wide boards after moisture readings are deemed low enough to begin work;not so with AD. The samples are 13 inches wide and only 3 inches long in order to make soakings more thorough .

[ian maybury]

Aha! :) Thanks again guys. I missed your point Mel - the moisture content does increase as kiln dried wood re-adsorbs moisture in a similar manner to during drying, but it produces quite a bit less movement - because judging by one of the Gene Wengert pieces mentioned http://www.cabinetmakerfdm.com/88415.html nothing much happens by way of movement immediately following the initial increase in moisture content. (another aspect of the hysteresis effect) Which is why he says it's better to start with wood that's a percent or two dryer than the likely EMC in the end user's house. I may have it wrong, but this effect is likely swamped by large changes in EMC. You're also saying that kiln dried wood moves less than the air dried variety in this situation - maybe to do with something like case hardening? This might explain the wearing off of the effect you've seen - the wood eventually relaxes.

I'd not seen Cabinet maker FDM before Jeff, it reads like really good resource. Great to see a fact based/professionally oriented journal. Thanks for that.

Agree 100% John on using a moisture meter and getting the situation under control. I bought a Mini Ligno more than a year ago, and a copy of Bruce Hoadley's Understanding Wood - and am looking at other options too. I have minimal epxerience with it so far though as most of the past year has gone into workshop set up. Our climate is pretty damp, but one positive is that we don't get a great deal of variation in average % RH through the year - so the EMC is pretty steady compared to the dry Winters and humid Summers you get in parts of the US.


ian

[Andy Pratt]

I'll put in my two cents in the following areas:

- Kiln dried wood is cool/popular right now. As a result (sometimes) uneducated suppliers or kiln operators have increased their rhetoric on why it is superior to air dried wood because it helps them with sales. Some of the stuff you hear is truly nonsense and makes you wonder if the kiln operator really understands what he is doing, and some of it happens to be spot on. I'm not delving into that argument but wanted to point out that there is a lot of misinformation out there as a result of this (not referring to this thread) and you are right to ask for data as opposed to just opinions because many people have bought their suppliers claims without doing the research on their own.
- I'll therefore keep my opinion on how much kiln dried wood moves vs air dried out of the equation and offer you my advice on the situation in general. It seems like you are looking for a "what should I do here" sort of answer so I hope I'm not off base giving one as opposed to providing data.

I want to understand every aspect of wood movement that I can, but that is an academic pursuit. For the effectiveness of my work, I only care that nothing I send out has a defect that is bothersome to the end user or advertises my work in a negative way. Toward that end I usually find myself planning for the "worst reasonable case" scenario with each board I use, and find that the kiln dried/vs air dried argument becomes irrelevant at the point where you do that.

The truth of the matter is that properly kiln dried and properly air dried woods are all going to be easy to work with and react in predictable manners that normal woodworking practices account for, and woods of either variety that are improperly dried are going to cause unpredictable results that are hard to detect before using them. So, if you are looking to do high-quality work, I wouldn't worry about how fast kiln dried wood reabsorbs moisture. Excess wood movement is easy to account for if you use high-quality construction techniques, and if you do that you are prepared to be wrong on a variety of assumptions you might make about the wood you are using, including the affects of kiln drying.

In other words, you will probably (and should) build everything to a tolerance that exceeds the claimed benefit of kiln dried wood anyway to account for other possible issues, so the disputed answer to this question is not something to let affect your work or how you deal with your suppliers. I am as curious to know as you but it just affects my mindset, not the way I will actually do my work. I would take the importance of wood acclimation as far, far more important. That is where you can really go wrong on a project.

[ian maybury]

I guess in the end Andy wood is wood - whether kiln dried or not. Which leads to the risk that if an unthinking supplier hands you a piece that was kiln dried but which has been around for long enough to recover all that lost moisture it's possible to run into trouble. Which suggests that it make sense to decide on moisture content limits for sensitive jobs.

'Trouble' of course is as you suggest relative too. Joinery methods allow in large part for movement - but against that it's got to be hard to sidestep the visual effects of movement in through tenons or breadboard ends or whatever. So it gets down to your design, and what you regard as acceptable. Movement in a rustic piece isn't the same as movement in a highly finished contemporary item.

Digging around in the numbers is no subsitute for a practical understanding of what's going on, or for having a practical working regime - but seems to have its place too. In that it tends to ground or set limits on the fairy stories if the right data can be found and used properly.

This to try to collect some snippets from this discusssion and the related digging in the topic:

1. Use of the term 'kiln dried' does not of itself define/commit wood as being at a given % moisture content.
2. Timber merchants do oversell - or at least often don't overtly manage the moisture issue in kiln dried wood.
3. Kiln dried wood gains and loses moisture in response to atmospheric humidity much like air dryed wood.
4. This gain or loss of moisture leads to the same rates of movement (up and down) as air dried wood. (Hoadley's Understanding Wood sets out how to calculate the movement - how fast it happens depends on the humidity of the surrounding air, temperature, coatings, species, air circulation rates and the like is is much harder to predict)
5. It as a result pays to check the moisture content before buying kiln dried wood.
6. The good news is that properly stored kiln dried wood (i.e. wood down around 8% EMC) exposed to the atmosphere seems to pick up moisture fairly slowly - at the rate of at worst about 2% increase in EMC (on average - it'll be wetter to the outside in practice, and less towards the core) in the first month, and 1% per month thereafter. (presumably lots less for hardwood in dryer weather) Wrapping in polythene etc slows this right down, exposure to liquid water massively increases it.
7. This still seems to suggest that it's best to get recently kiln dried wood if you need it down around 7/8% - for example for furniture going into low relative humidity conditions.
8. Kiln drying done well is kept slow enough and includes a finishing step to reduce the moisture gradients that arise during the drying process, and hence minimise any residual stresses. Poor drying can leave high stress levels in the wood (case hardening and the like), or even honeycombing or cracking
9. Despite this it's still advisable to allow some time for kiln dried wood to equilibriate in your shop before working it, or after a piece is cut open. That is to allow the moisture content to become more or less uniform through the pieces.
10. One issue with this is that the wood can't ever fully equilibriate if the humidity in your shop keeps on changing (as it may naturally do). This suggests staged machining etc where possible - but it clearly often doesn't become a practical issue.
11. Notwithstanding (3) it seems that hysteresis means that kiln dried wood hardly moves (expands) during the first 1 - 2% increase in EMC when it starts to re-adsorb moisture. (over the first month or more)
12. One result of this it seems is that you can minimise movement in use by starting with kiln dried material at about 2% below the EMC you want the wood to equilibriate to when the work is installed. (i.e. arrange for it to return the target EMC from having last been dried to a point just below it. e.g. see the link to Gene Wenegert's piece in CabinetMakerFDM above)
13. This (if we're running a super precise humidity controlled set up) seems to determine the % relative humidity a shop needs ideally be held to. i.e. if it's air conditioned. (there's a direct relationship between the EMC wood settles to and %RH - refer to the usual % RH/% moisture content (EMC) graph that's published fairly frequently e.g. in Hoadley again)

Please shout if any of the above makes no sense...

ian

[Rick Alexander]

I'll throw my 2c in here as well. I nearly exclusively use wood I have had a woodmizer guy at some point mill for me on my property. Many years ago I had approximately 3K bf red oak kiln dried for me at a chair manufacturer when they just added it to their stock in their kiln for a fee after I had already air dried it for approximately 18 months. Afterwards about 3/4 of that we stored in my dad's basement (stickered by the way) which is climate controlled and the rest I stored in my basement under my house that isn't climate controlled. I fully expected to have issues with the basement stored stuff so I was careful to use dad's stock for anything that I glued up for panels and the stuff in the basement for face frames and rails and styles. This went on for about 3 years until finally I ran out of the stock at dad's and began to use the basement stuff for panels that were not for customers but for my own and family pieces just in case I had an issue with a door panel or something. In the couple years or so since I finished using that basement stock - which by the way is in Georgia - not a low humidity environment by any stretch of the imagination - I've not had a single panel split. I have had a couple of doors warp over time but overall I'm not unhappy with the yield because frankly I've had doors warp using fresh kiln dried as well. It just happens sometimes and I'd say it's in the 5% range for me using air stored wood.

I will say however the basement stuff does take longer to "relax" in the shop to the point that it's ready to mill and dimension without so much movement right away. I give it a couple of weeks in the shop after I plane it initially to close to the final thickness before I start working it up and I think that avoids a lot of trouble. I start out at 1 1/8 inch rough cut exclusively so I will have room to flaten completely. Initially I plane down to 7/8, cut close to dimension, joint flat and then plane down to final thickness and finish cutting to dimension. So my relax time is between the 7/8 plane and the first dimension steps. I've been doing it this way for as long as I can remember now. I don't get quite the yield from the tree but I seem to avoid a good bit of waste on the back end this way.

I guess what I'm getting at here is I keep my wood far longer than the typical guy because I do it in large batches and use it over time. I just don't see much trouble air storing it after it's been kiln dried. In fact in a good many cases I don't have trouble with exclusively air dried stuff if used in certain circumstances like face frames and solid backs that are ship lapped or t&g panels where I plan for expansion and contraction in the design of the piece. I don't know I'd fully trust air stored on customer pieces still but I feel better about it than I use to.

[John TenEyck]

Not many shops have climate control at all, much less the ability to adjust the humidity so that a particular piece will be built at an EMC 2% below the expected final location. That just seems unreasonable; I wonder where the 2% came from, too. I think it far better, and easier, to just make sure your wood is at EMC with your shop. The humidity in my dehumidified shop changes very slowly since it's in my basement. Others may not be so lucky. Anyway, wood that is in harmony with your shop, whether AD or KD, doesn't matter, will be able to be worked without bending, warping, etc., unless it has other internal stresses in it. Good practice says to mill it oversize and let it sit overnight or more, but I've rarely found this to be needed if the wood truly is at equilibrium with my shop. Future expansion/contraction must be anticipated in the design and construction of the piece - the worst case scenario discussed above. For example, if you are building the piece in Summer and the EMC is 10% in your shop you would be wise to pre-stain or even pre-finish the panel of a raised panel door, in anticipation of witness lines showing when it shrinks next Winter when the EMC is 6% in its new home. Or if you are building an inset drawer in the Winter when the EMC is 6% you would be wise to actually calculate how much it will expand next Summer when the EMC is 12%, and allow for it as you build the piece. It isn't rocket science, but it's not black magic either. Some smart guys have done the research and made the information available to anyone who cares to study and use it.

John

[Mel Fulks]

Ian,that is a good summation .Except that it leaves out what you acknowledged earlier about the resistance to movement in KD wood due to the case hardening effect or some unknown (to me)factor. I wrote yesterday that by extreme measures like soaking that disappears and KD and AD will finally behave the same way ,AFTER EXTREME MEASURES. It's easy enough to actually measure the wood movement ,instead of the moisture. We used to saw off a short piece of just received wood ,measure the width and then put the sample in a warm room overnight and remeasure.Crude but effective in that it addressed actual change....CHANGE WE COULD BELIEVE IN! Sorry.One thing I never see mentioned are the changes brought by modern glues that work well at temperatures as low as 45 to 55 degrees. When I started working shops were warm .Many of the larger companies burned scrap and even shavings to produce heat and electricity. The smaller company's at least had a warm room used for acclimating and gluing .In recent years I've worked in shops that ,in winter ,never get above 55 degrees 6 feet above the floor. That might be okay for the glue ,its not the best for the wood and trying to produce good work.

[ian maybury]

Great to get some experience based input - mine is limited. (in that i've just been using wood as received without measuring anything - and on stuff that's not sensitive)

I didn't intend to deny the resistance to movement of kiln dried wood Mel, but it perhaps got a little buried in the point about minimal if any movement occurring in the first 1 - 2% of moisture increase after drying due to the hysteresis effect. Guessing - but maybe what happens is that since hardwood gains moisture more slowly than the worst case softwood rate of re-adsorbtion i pulled from the linked USDA book/paper (even more so in less than worst case humidity conditions) that's what you were seeing in kiln dried wood. In that it seems like it could take quite a few months for that 1 - 2% to be exceeded. Once it gets wetter/past that the effect disappears and normal movement is resumed.

Air dried wood probably won't often show this effect since it's typically on the way down to equilibrium with the atmosphere when used - not at least unless it dries right down below, and then the weather/shop gets much more humid and it starts to pick up moisture again.

Measuring a sawn off sample (presumably from the middle of a board, as the end won't necessarily be representative beacuse they lose/gain moisture so much faster) sounds like a really practical and direct way to get a handle right now on the condition of the wood we have. That's another for the list Mel. :)

The big effect of lower room termperature will be to raise the relative humidity of the shop air I guess (%RH) - and hence to raise the rate at which wood wil take up moisture and the EMC at which it will finsh.

The 2% below point John came from the linked answer by Gene Wengert to a question on CabinetMakingFDM. It's presumably not that critical/gilding the lily/ only relevant in very specific situations (where any movement would be an issue, suggesting in the unlikely event of AC that controlling to the EMC should be fine) given that so many stay out of trouble despite taking minimal precautions. As in if there was a high incidence of problems the chances are that practices would have been forced to respond long ago.

I guess in the ideal (and unlikely) scenario it would be dead simple - the wood when bought would be at an EMC/moisture content that matched the %RH of your shop, and your shop would match the % RH of the environment where the work is to end up. i.e. the wood as you say would remain in equilibrium throughout. It's mismatches between the EMC of the wood and the %RH of the environment that drives movement.

What's dawning is the realisation that hardwood seems to take up moisture much more slowly than i had initially thought it might - and that maybe it's this that prevents most of us running into frequent problems. Especially since some % of problems is presumably down to bad kilning practices causing stuff like case hardening too.

For sure it's not rocket science. There's good information out there, but it's still not a complete science in that while the principles are fairly clear and it's possible to pretty accurately predict how much movement is likely with a change in EMC, it's damn difficult given all the variables involved to predict how quickly it's going to happen. e.g. it's hard to predict without reliable rules of thumb combined with simple shop based tests like Mel's just what you have bought.

Thanks for the input on your experience with wood stored long term Rick. That's good news too, in that it again suggests that the whole deal while needing common sense care isn't hyper sensitive. In favour of your situation might be that a basement won't be subject to much by way of temperature changes, or to rapid air changes - it'd be interesting to know what %RH and temperature your storage is typically at, and whether it does or doesn't move much. You are presumably placing customer work in air conditioned environments, and not seeing problems there either - and that could be quite a lot dryer than your shop....

ian

[Kevin Jenness]

Having lumber at the proper MC for its intended use is an ongoing problem. Commercial KD lumber is often at a much higher MC when sold than just out of the kiln depending on storage conditions and time in storage. The first thing is to have an accurate assessment of the MC. Pin meters are the most common, but you really need probes that will penetrate at least 1/4 of the lumber depth to get more than a superficial measurement, and half the lumber depth if you want to know the core MC. Pinless meters are an alternative (and more acceptable to sellers). Drying and weighing samples is the definitive technique but not always practical.

The second thing is having a way to get the lumber to its desired MC. If your shop is climate controlled, then stickering and adequate time, perhaps supplemented by air movement from a fan, will do it. If you're in a hurry, a kiln is the way to go. At work, we have a small dehumidifcation kiln that runs at a maximum temperature of 40 C (113 F) with a circulation fan. In my limited experience it takes at least a week to get 4/4 hardwoods from 11-12% down to 6-7%, longer for greater thicknesses.

I am just finishing up a 600 board foot solar kiln at my home shop to deal with reconditioning lumber as well as some drying of green and partially air dried lumber. I don't intend to air condition my shop, but at least I can get the lumber to the correct MC prior to use, and store it wrapped in the shop to maintain its MC.

[Mel Fulks]

Some say some good things ,existing now, were made before moisture meters and even before kilns!

[John TenEyck]

Some say some good things ,existing now, were made before moisture meters and even before kilns!

Those are the ones that are still around. The stuff people built who disregarded moisture and moisture change or good design principles self destructed over the years. We've all seen panels that were fit so tightly that the frame busted, or drawers and doors that refuse to open in the summer, etc.

John

[Mel Fulks]

That's true ,John. I think it would help to have some other members cut off a short piece of kiln dried wood ,take a moisture reading and measure the width of the sample. Then soak it in water overnight and remeasure ,may be no change in the width but Im betting meter reading will be high. Is the reading useful? What I see is that everyone can afford a meter,few buy enough heat for their shops .I worked a long time in shops with good heat before the proliferation of moisture meters in shops with inadequate heat. In four decades of commercial woodwork,mainly architectural,what problems I've seen with wood came from inferior species,air dried stock, cold,and buying from dealers the management knew were unreliable.

[John TenEyck]

You'll get no argument from me, Mel. A MM doesn't make up for ignorance.

John