Can I dry down to 6-8% in my heated building?

[Brad_bb]

So not for any large volume...but for my own projects, can I take  1x or 2x hardwood lumber I've air dried outside and bring it inside my heated workshop stickered on shelves, will it come down to 6-8% that you need for furniture over the winter when it's dry and heated?  I've seen other lumber shrink in the shop, namely my 2x DF loft floor.  I see a lot of talk about Kilns and how they wring out those last percentage points....  Will it happen in the heated shop too just take longer time?

[YellowHammer]

Yes.  Look up EMC calculator on the web.  If you can maintain 70°F and 30% RH then the EMC is 6.2%.  Your wood will asymptote to that, given time.

[GeneWengert-WoodDoc]

If you have 6.0% EMC, you will likely only get 7.5% MC in a thick piece.  It takes heat and a lower EMC to dry the core in a reasonable time.

[Brad_bb]

I'm thinking over a few months at least.

[Jim_Rogers]

As mentioned you need to keep the moisture content of the air in the shop low so that the wood will dry. If the shop air is saturated with moisture from the wood, the wood will not dry any more. You may need to put a dehumidifier in the shop to keep the moisture content down. Dry air dry wood, moist air moist wood.

Jim Rogers

[petefrom bearswamp]

I have dried to 6-7 percent with my homemade dehum kiln successfully, BUT after several months in my high hum shop MC is back up higher.
My shop is 32x64 10' ceiling too big to dehum practically
gets to high 80s humidity in summertime.

[scleigh]

Brad, I've been able to dry white pine down to 8% in 2 weeks in my basement beside my wood stove. I'm gonna put a barrel fan in front of my stove, then a rack of air dried red oak and a dehumidifier behind the rack of red oak. Hoping to dry it down to 8% and build a table.

[warren46]

I would like to add a comment.  There is nothing magic about  6 - 8 percent moisture content for furniture.  Good furniture is constructed so that the wood can move as the moisture content changes either to a higher content or dryer.  I have built a lot of large furniture pieces with air dried lumber and not had a single piece crack or warp.  I suspect the moisture content of the lumber when I constructed the furniture was closer to 12 percent than 6 percent. That is why wood workers use frame and panel construction and bread board ends.

In other words, build your furniture for wood movement and do not sweat the moisture content (subtle pun).

[nativewolf]

One of my good friends is named Warren and he too is full of good advice.  Hmm...must be something about that name.

Anyhow, yes the early antiques were not kiln dried and some of ours are getting close to 200 years old.  Now...if you could make them 5 year old proof by kiln drying them that would be helpful.  Forget the ol MC and EMC and talk about 5 year old proof ratings, how long do I have to kiln dry it so a 5 year old can't hurt it  :D

[YellowHammer]

Remember that one of the most important things about a kiln is sterilization.

[Brad_bb]

Heated shop here in winter, air is awfully dry.  I think I got my answer - yes.  Summer could reabsorb if in humidity, unless I keep it in the Air conditioned room.

I built a Walnut bedside table a few years ago.  When built the bread board was flush with the glued up top boards, by the first winter, It shrank 1/8th in.  Following summer it expanded again but not quite flush.  Next winter it shrank a bit again, but not as drastic as the first winter.  Now it's a little under 1/16th on each side.   Looks fine.  In winter when it's most prominent, You'd just think I built it that way.

As far as Sterilization, I figure power post is what you're trying to kill mostly.  What I've learned is that powder post, while seeing piles of sawdust may be annoying, they are rather slow moving most of the time.  So once a larvae leaves, it takes another adult laying eggs to get more.  I'm probably ok treating with Timbor or Solubor(which I haven't used yet but want to try).  If you're selling wood, you don't want any, but on my stuff a few pin holes don't bother me.  I did my shop window and door trim all in barnwood.  I had some powder post activity, but after applying the finish (two coats of general finishes high performance FLAT- a great choice for finishing barnwood by the way, just make sure you keep it well mixed so the flattening agent doesn't settle to the bottom) new ones don't come anymore.

[warren46]

I built a Walnut bedside table a few years ago.  When built the bread board was flush with the glued up top boards, by the first winter, It shrank 1/8th in.  Following summer it expanded again but not quite flush.  Next winter it shrank a bit again, but not as drastic as the first winter.  Now it's a little under 1/16th on each side.   Looks fine.  In winter when it's most prominent, You'd just think I built it that way.

So if the same table had been built with 6% lumber then in summer when the humidity is higher the breadboard ends would be shorter than the field.  That is why the moisture content of the lumber is not as important as the construction that allows the wood to move without causing the piece to self destruct.

[moodnacreek]

I am confused about  'bread boards'. What is often seen in amateur built board table tops are grooved end boards glued on to finish the ends but the grain runs the other way. May be with quarter sawn but not regular lumber. If the table top shrinks, it's broken. While I am not a cabinet maker, I tell my customers not to use bread boards.

[Ianab]

What is often seen in amateur built board table tops are grooved end boards glued on to finish the ends but the grain runs the other way.

Gluing breadboard ends firmly in place is a rookie mistake. As you know, wood will move seasonally in width, but not length, so bad things are going to happen in that situation.

There are ways of fixing a bread board properly. The middle can be pinned and glued, then the ends pinned with elongated holes so they can slide. This is what Brad is describing where the ends don't match up exactly depending on the season. But the piece doesn't fall apart.

[Don P]

As a practical day to day matter I've had far more shrinkage related problems than swelling ones. I've had fewer regrets and prefer to start on the dry side of emc especially with things like flooring and paneling. Air dry I'll get to around 12% here, with wood heat in the winter it'll go to around 7-8%. As you experienced if you approach emc from the dry side there was less movement the second year in the breadboard. In other words I would rather be approaching emc reabsorbing moisture than still shrinking to a new moisture content.

[mike_belben]

All i can tell you is there is nothing thats 5 yr old proof.  Not furniture, not a locked iphone, not an air craft carrier. 

You want to see a D9 explode?  Put a 5yr old in it.

[PA_Walnut]

I think a lot depends upon what species and what you are using it for. I used air-dried material all the time for my Maloof rockers, but give them plenty of time at each step along the way.

As pointed out, many (mostly all) historic pieces were made with air dried wood and have stood the test of time over centuries. Some, even many, have issues like cracks, cups, etc. But, proper build techniques can mitigate most issues, but wood WILL move, whether air or kiln dried.

Science, understanding and techniques evolve, but wood has been the same since the beginning of time. It's non-negotiable and rather simple. Understand your material and operate within it's boundaries and you'll be fine.

Bugs/sterilization are a completely other matter. Again, simple rules.

[GeneWengert-WoodDoc]

Although old furniture was not made with kiln dried lumber, the wood was often put in the rafters of a shop.  For example, see Colonial Williamsburg.  Also, the humidity in a shop in the old days was fairly dry, so stored wood and wood in manufacturing did dry well...a stove or fireplace heating system is continually bringing in outside 12% EMC air, and then the heat dried both the air and wood out.  Further, the old homes that wood was in was more humid than today with our present central heating.  Many antique pieces of furniture have indeed been damaged when they moved into our drier homes today.

Note that the outside humidity is around 12%  EMC, in both summer and winter, so any heated shop or home will be drier than that.  So although wood may not be kiln dried, it will be drier than 12% MC.  If a shop is 50% RH, that is 9% EMC.  Most homes today that are heated in the winter are close to 7% EMC.  If wintertime temperatures are under 30 F outside, then closer to 6% EMC.

In the old days, woodworkers understood moisture and shrinkage, so they were careful to dry the wood in their shop to a level expected in use.  As stated in a previous posting, they also tried to accommodate some wood movement in the design, but drying beyond air drying was much more a key to them.  It is surprising how often this fact is ignored today when we look at their manufacturing.  And they did this without moisture meters and computers.  They were not dumb.  They knew that wood moves when the MC changes, so they needed to dry the wood beyond air dried levels.

The use of the concept of kiln drying for furniture woods is only around 150 years old.  It became important when furniture factories and rapid production became popular—no Longer any time to dry the wood in the rafters or while manufacturing.  Kiln drying of softwood lumber became important when lumber was shipped a distance- -lighter weight and the lack of fungal stain became important, but the kiln dried 15 % MC level for construction woods is just a bit over 50 years old.  It had more to do with final uniform size and warping control.

Bottom line.  Furniture, cabinet, etc. wood has been intentionally dried below 12% MC air dried levels for centuries, but using kilns to do this is relatively modern.

[GeneWengert-WoodDoc]

A note about practical,wood movement.  Assume we have a piece of wood dried to 6.5% MC in a home in the winter.  Now in the summer, the environment goes to about 9% EMC, but the wood will actually only increase to 8% MC due to hysteresis effect on MC and on swelling.  Then the next winter, when the EMC drops to 6.0% EMC, the wood will likely only get to around 7.0% due to hysteresis effect.  Plus this moisture change is slow- -6 months. 

This moderation is why we might see moisture issues with new furniture (fast and large change in MC) but seldom with pieces over a year old.  Wood can actually tolerate slow MC changes without as much movement as we would see with fast changes.

[PA_Walnut]

Nice write-up Gene. I agree with all of that.

A key to what Gene said, is that when air drying, the gave (we should) allow ample time in shop environment to dry. My shop's RH is right away 30% right now which will dry material down...WAY down. So, I allow it to sit in there for a while before starting to mill it. Also, when I mill it, I do so in stages as to let is further acclimate.

I have three various moisture meters (two pinless and one Delmhorst J2000 pin type) so I am really able to know where I'm at with MC. I'm NOT looking for 6-8% MC on my build material. 8-10% is fine and I never have problems. Construction methods are used that keep movement in mind.

I have a two board curly maple dining table top that moves at LEAST 1/2" from summer to winter. The breadboard ends are 1/4 proud to the table in summer and vice-versa in the winter. I designed them with very long slots for the pins and no glue. So far, after nearly a decade there's no cracks or issues. I also have a single board 5/4 walnut table that is 35" wide with breadboard ends...again no issue. I designed the ends with a lot of movement in mind.

On sterilization, particularly since I like air-dried walnut, I'm diligent to use no sapwood and I've yet to see any in the heartwood. Walnut seems to be disfavored by ALL living organisms except humans.  :D

Gene, do you know if the Thousand Cankers fungus and/or twig beetle effect walnut heart wood, or is this specific to the outer layers of walnut? I've yet to see any affected trees here yet. Thx

[YellowHammer]

Very informative posts.  PA, I don't know if you have pictures of the table but I would love to see them.  I have been looking for such pics for a while for the "Tips" page of my website, and all I can find are drawings, cartoons, or predictions of what will happen. No before and after photos of repeatable, cyclical expansion.  Or if anybody else has pictures I'd like to get them. 

[Brad_bb]

Yes my bread boards are glued pin in the middle with non glued pins with slots on the outsides.  Breadboard is not glued.  It cycles without a problem.

[PA_Walnut]

Hammer,
Yes, I will take some pix. I have several tables that will make good examples. My feet are propped up on a curly maple coffee table right now that has some great examples, including a peg that didn't allow for enough movement, which cracked the boards...standby. Will take some pix and post asap.

Very informative posts.  PA, I don't know if you have pictures of the table but I would love to see them.  I have been looking for such pics for a while for the "Tips" page of my website, and all I can find are drawings, cartoons, or predictions of what will happen. No before and after photos of repeatable, cyclical expansion.  Or if anybody else has pictures I'd like to get them.