Minimizing internal stresses

[Josko Catipovic]

I have a special (to me) 12/4 14" QSWO plank I'd like to resaw. It was stickered in an outside shed for 3 years, then brought into the shop ~ a year ago. It reads 10%RH. How should I store it to minimize residual moisture gradients and internal stresses befoe I resaw in in 6 months or so? A friend mentioned wrapping it in saran wrap for the duration and storing in the shop, which should be close to 30%RH for most of the winter (on Cape Cod).
I'd much prefer not to cut test sections to check stresses, but I'm game to buy a tool (up to $500 or so) that could check this noninvasively.
(FWIW, the resawing tool is a 5 hp Laguna 18 with an appropriate fence and sliding support. It's cut that width oak before. )

[Rich Engelhardt]

Sorry - wrong forum.
Didn't mean to intrude on a serious question.

[Jim Becker]

Josko, if there is inherent stress in the board it's "going to be there", but you can minimize impact by keeping it flat on stickers so there is good air flow to help it continue to equalize moisture throughout. But at 12/4, that's harder to do, especially without the help of a vacuum kiln or other kiln format. Plan your resawing carefully and don't expect to "get there" quickly. It's likely that you'll have to resticker to allow for moisture equalization during the process as you expose those inner areas that are likely to be higher moisture content than the exterior surfaces.

I'm not familiar with that plastic wrap thing, so I"m not going to comment on it.

[Richard Coers]

White oak is one of the most difficult woods to dry because of the tyloses in the cells that restricts the moisture from being removed. And at 3" thick I'll guarantee it's not 10% in the center. Also wood moisture is not relative humidity, it's a moisture level in the cells of the wood. Relative humidity is the percentage of water in the air and changes with temperature.

[Kevin Jenness]

I would resaw it now. You will be able to assess the mc at the center and the two pieces will, if not completely dry now, continue to stabilize faster than if left in one piece.

You said "it reads 10% RH". I assume you meant mc (moisture content). How did you get that reading? A pin type meter, unless using pins that reach near the center, will not tell you all that much. A pinless meter designed for thick wood will give a better idea, but still only an average reading. I don't know of any pinless meters that will scan deeper than .75" but they probably exist.

3 years outside and one year inside would be enough to thoroughly dry many woods, but as Richard said white oak is a special case. Wrapping the piece in plastic would allow it to slowly equalize its moisture throughout the thickness, but the overall mc may still be higher than needed.

Spurred by a recent thread on workbenches I started in on reading Chris Schwartz's The Anarchist's Workbench in which he describes building a bench with a 6" slab of oak that had been drying for years but was still at a very high mc at the core. I don't know why he chose to do that, and the bench top may still be drying for all I know, but it might be pertinent to your situation.

[Josko Catipovic]

Thanks guys. I did indeed measure 10% moisture on a Wagner 930 meter, which read '10' on both shallow and deep settings. Here on Cape Cod, we have very humid summers and 'typical' dry winters, so I was thinking fall might be a best time for major resaws, as wood surfaces re-absorb summer humidity, perhaps equalizing a bit more. I'm also going to try saran wrap, with the idea of reducing the moisture gradient as much as I can. I have no problem waiting on this one plank, but it would be a 'bummer' if I ruined it by rushing.

[Scott Winners]

This is one of those times where I think of the old saw about "one inch per years of thickness" and some moderns saying "Well, that is one inch per side so 8/4 should be dry in one year." Old school a two inch board should take two years, stickered. As stock gets thicker it takes even longer, and as already said white oak is a bit of rascal. I think if the old timers could dry 8/4 stock in one year the old saw would would say so.

If this board really has sentimental value to you, is there a way you can bring it, as is, to it's final climate controlled destination, and season it three years more? If you can do that you should be able to resaw it, and then bring it back into the final climate controlled area to settle down a bit without much in the way of drama except for internal grain stresses.

The value that controls for both temperature and relative humidity is "equillibrium moisture content." Searching on EMC will get you a bunch of hits to the US Forest Service. They probably have a separate table for white oak, I haven't looked. Once you have an EMC table for white oak open on your monitor you can look up your wintertime indoor thermostat setting and observed RH for the wintertime EMC the white oak stock will move towards, and find the EMC value for your summer thermostat and observed RH to find the EMC the white oak will move towards in the summer. Once your board is inside that range, all the way through, you should be able to work it with minimal concern, unless the grain is wonky.

I don't know of a way to measure the MC deep in a board without cutting it open. I burn about 8 cords of spruce every winter. To really 'know' what I am working with I split open a seasoned split and then measure the MC on the freshly exposed face, near the center of the length, and near the bark if there is any left on the split. With solar kilned one seasoned spruce firewood (16" length) I typically see +/- 12% at the surface and ~16 % in the center.

I did buy a 10 foot length of 16/4 Doug Fir about a year ago, 13.5 inches wide to make a chop for my leg vise. I _know_ that plank had been air drying in my local purveyors unheated barn for two years minimum because the boot print I put on it in 2018 was still there when I bought it in 2020. The mill mark said s-GRN, so the plank would have been dried to real close to 20% MC before it was surfaced. Once I pulled my vise chop off one end I ripped the remainder on the pith line and got all 4 legs for my next work bench out. On center, with two years to air dry after having been kilned down to near 20% MC, my firewood meter was showing me 20% MC in the center of the plank. I could also smell turpentine when I was sawing it, a reliable indicator DF is at 20% MC or above.

The upshot is I think your 12/4 white oak is not dry all the way through. The center might be close to your local outdoor EMC for Cape Cod, or maybe even still moister than that.

I have never tried wrapping a single board in saran wrap so cannot comment knowledgably.

[David Utterback]

As others have said, wait if possible. After air drying lumber, I liked to cut an inch or 2 from the length to check the internal moisture. If you have a plan in mind, you might be able to cross cut consistent with the plans and then check the internal moisture. Good luck.

[Scott Winners]

As others have said, wait if possible. After air drying lumber, I liked to cut an inch or 2 from the length to check the internal moisture. If you have a plan in mind, you might be able to cross cut consistent with the plans and then check the internal moisture. Good luck.

I have actually done exactly that. I have some white oak (no sentimental value) to replace my office desk cut to length for the new desk I want to build, but my cut a little long almost to length peices are stickered in the office where my computer desk is. They are in the way, but I don't want them moving after I build with them, so they are acclimating to the environment where they will stay.

[Kevin Jenness]

After air drying lumber, I liked to cut an inch or 2 from the length to check the internal moisture.

Because lumber dries far faster through the ends than the side grain (that's why we get end checking) a 2" cutoff is unlikely to give an accurate mc measurement for the whole plank. Your best bet is to weigh the piece monthly. When the weight stabilizes you will know it is in equilibrium with your shop environment.

[Tom Bender]

You are planning to resaw it to 14" wide lumber? How thick, how long and do you know what you will be making from it?

[Mark Gibney]

Like Tom above, I'm wondering what resawing you plan on doing? - split it in two equal halves of approx 1 1/2" x 14"?
Or veneers?

I resawed several 8/4 WO boards last week for making face frames (there was no 4/4 rift WO available).
All the boards curved and twisted like crazy. My understanding is that case hardening is very common with kiln dried WO, like a loaf of bread from the oven. When you split that open, it moves.

If your board is air dried it probably won't be case hardened and might be more stable when you resaw it.

[Robert Engel]

Yes, you need to clarify if this is veneer or lumber. If its lumber, you may be in for some dissapointment.

Re: veneer IMO the MC is not that critical (I've never measured it once), its holding it and allowing it to reacclimate.

THAT is when I would wrap it in plastic. Not Saran wrap -- I get the stuff on a roll from Home Depot in the moving supplies dept.

I use 1/4 thick stickers and tape the stack together, maintaining sequence. Sandwich the stack between two flat boards of equal width and length.

[Josko Catipovic]

It is a single resaw for a bookmatched hall table. Sounds like the wise thing is to let it sit a few more years. I've got it stickerred in an unheated garage with some slings on it so it can be weighted periodically.

[Scott Winners]

It occured to me several days ago you might be able to bring that plank into the climate controlled part of your home to finish seasoning if you could put a shelf bracket under it on every stud, maybe a high shelf in the laundry room or something? Little double sided tape? I do not keep as tight a control on the HVAC in my garage as I do the rest of the house. I get much wider annual EMC swing out there than I would tolerate in the house.

[Tom Bender]

Assuming that it's rough sawn, and if it's flat now you might try this;

Plane the outside faces to get good surfaces and to remove a little of the surface effect (driest and acclimated)

Joint an edge to make it handle well in resawing

Resaw and sticker for a few months

If it's going to fail, just get it over with.

[Joe Jensen]

There are lots of myths and miss-explanations. A few things on wood. 1) Wood changes size with changes in humidity. If you look at a slice wood showing the rings and look at the rings, the wood will move a lot in a growth ring and a lot less between growth rings. This is why a slice of wood will always crack in at least one place looking like someone took a slice out of a pie. 2) Wood finish will not stop this movement. Humidity will always get into the wood. Finishes slow it down but it will always move. 3) The movement is predictable when the grain is straight. Nearly all species move 3X More with the grain than across the grain. If you resaw a piece with straight grain its unlikely to move much. Resaw a part with some curl or crotch or burl or where a branch connected with the main tree trunk and it will move like crazy. This is because within that piece as it dried some wood will be trying to move 3X more than the rest. When the board is cut that pieces will be more free to move. 4) You can plan for this when cutting. I love figured wood and it's my go-to. But it will move so I cut each part oversize and then work to thickness planning to joint an plane a lot to get it flat. 5) You need to design for this movement. I built a kitchen table from plain sliced 6/4" red oak. It's 37" wide, finished on all sides with polyurethane and even in relatively dry and consistent humidity in Arizona it changes width 3/8" every change of season. If I didn't plan for this in the design and construction the top would split. A great book is "Understanding Wood".

[Josko Catipovic]

Screwed up my courage and did it: planed both sides, squared one edge, and resawed down the middle. 5hp L18 with a 1 1/4" Resaw king cut it like balsawood, although supporting the 12' plank was a bit of an issue - glad there were three of us. It cut fine, although now I have a ~1" bow (towards the outside) in the middle. Moisture meter read '10' on the outside (before the cut) and 12 on the inside. It's now stickered with ample weight on it in an unheated garage. Hopefully the bow will straighten as moisture equilibrates and and it won't crack. Bookmatch looks better than I expected.

[Tom Bender]

That's a pretty good result. With the moisture readings so close it will probably not do anything more and you will just have to deal with the bow.