Wood Drying Question

[John Crawford]

Hi Folks:

First time poster here.

This is also my first time building something large (a heavy workbench from construction lumber, much like the Schwarz $175 bench), and drying out a pile of lumber. I hope you can tell me what I am doing wrong so this won't happen again:

Bought a pile of #2 "select" douglas fir, 2x8x12s from a local lumberyard (not a home center). Brought it home, stickered it, painted the ends with latex paint. Put it in the basement, where humidity is 50%.

2 days later, major checking: some 2 or 3 foot long cracks, some boards cracking in the middle.

Any suggestions for where I might have gone wrong?

And: for boards just starting to check, does it help to cut off the crack, and repaint the end?

Many thanks!

[Kevin Bourque]

50% humidity is the problem I think.

That wood was probably kiln dried to around 6-8%. Now all of a sudden it's being saturated with moisture and it splits like an over watered tomato.

[Mel Fulks]

Gotta go the other way on this one. If it is construction grade fir it's not kiln dried to as low a percentage as cabinet or millwork grade. Inside my house is often RH of 50 percent . I think it's drying that's causing the cracks.

[John Crawford]

Yes, it is definitely the drying that is causing the cracks. Is this normal behavior for construction lumber? I have been in people's shops who are fastidious about keeping humidity at 50%, so I thought this would be a decent level....

[Mel Fulks]

We have some members who can quote the percentage specs used for construction lumber .But I'm not one of them.
its normal for the wood to shrink ,how much the stuff cracks will vary .Some pieces probably might not crack at all.
I would just condition it and use it .

[Andrew Hughes]

If your 2x8 are cut close to the pith or middle of the tree they are more likely to split when they dry,just like others mentioned.Andrew

[bill tindall]

This is likely the correct answer. And if this is the case there is nothing you can do to stop it. The juvenile wood that forms as the tree is first reaching for the sky suffers exceptional shrinkage as it dries. In hardwood lumber production the centers of trees are "boxed out" during sawing and sold for pallet lumber for it is useless for furniture due to splitting and checking.

[Danny Hamsley]

Most construction lumber is KD19 if you look at the grade stamp. This means it was kiln dried to 19%.

[Cody Colston]

Too-rapid drying is causing the cracks although they may have already been present, you just couldn't see them. Yes, cutting off the checked ends and re-sealing will help.

[Richard Coers]

Construction grade lumber will get you a construction grade bench. Expect checking, twisting, and warping from construction grade lumber. Furniture grade wood will give you the result you anticipated. Construction grade just barely meets the 19% moisture level, and as mentioned, it may be cut way too close to the pith of the tree. You can use lower grade for the base, but may want to consider a plywood top. You didn't do anything wrong, except maybe purchasing wood that is expected to crack when it goes full dry.

[Scott T Smith]

Hi John; welcome to the Creek!

I'm a kiln operator; it sounds to me like your lumber was wet or very green before it went into your basement. Typically you cannot damage lumber drying it from 19% down to 8%; you can however easily damage it in drying from 35% down to 8%. Fir is usually very forgiving to dry, so your experience is somewhat perplexing.

Typically lumber is dried in stages, in specific environmental conditions (temp and RH%) for each stage. As it progresses during the drying process, the temp is increased and the RH% is lowered. The last stage is below 25% moisture content, when the temp is the highest and the RH% the lowest.

Here is what I would suggest. First, buy a moisture meter. You can get a decent one for less than $100.00 and it is a tool that every woodworker should have. If you don't want to buy one, see if you can find a fellow woodworker that has one. Not all lumber measures the same way; the better meters will allow you to calibrate the meter for the species (and temperature on the really good ones) of the lumber.

Second, take the lumber back to the lumberyard and see if they will exchange it.

Third, take your new meter along when you pick out your replacement lumber. Try to find the driest (and straightest) boards that you can, and look for boards that are free of hear center (FOHC); ie no pith wood in them. Buy extra, as Richard stated you're going to get some rejects as the lumber drys. Also, but lumber a couple of feet longer than you will need.

Fourth, if your lumber is above 25%MC, cut about 8" off of each end (to get rid of any ends that have already started checking but are not visible to the naked eye), paint it and stack/sticker it outside under cover (or in a garage) and allow it to air dry down below 20% (and 16% is better) for a few weeks.

Fifth - transfer the lumber into your basement - also stacking/stickering it until your meter reads below 10%MC.

Then build your bench.

At 70 degrees and 50% RH, lumber in your basement should equalize to a MC% of around 8.9%, which would definitely be suitable for a workbench.

[Jeff Duncan]

Construction grade lumber will get you a construction grade bench. Expect checking, twisting, and warping from construction grade lumber. Furniture grade wood will give you the result you anticipated. Construction grade just barely meets the 19% moisture level, and as mentioned, it may be cut way too close to the pith of the tree. You can use lower grade for the base, but may want to consider a plywood top. You didn't do anything wrong, except maybe purchasing wood that is expected to crack when it goes full dry.

Mostly agree with this, only thing I'll add is it also may have been poor quality lumber to begin with. Usually it's the box stores that carry the junk wood, lumber yards usually have the better quality stuff.....at least around here;) But these days a lot of the construction lumber seems to be super fast growing stuff which just isn't going to be stable. If the growth ring spacing is larger than your pinky finger....you know your doomed:eek:

good luck,
JeffD

[Danny Hamsley]

Some douglas fir construction lumber is sold green, not kiln dried to 19%.

[joe milana]

2-3' cracks right down the middle sounds just like wood cut right through the pith. 85% if the big box wood around here is just that, and every 2 x in the unit will be exactly the same. (see drawing) They must cut trees barely large enough to get a 2 x 4 out of. 110% Guaranteed to crack! Been a while since I read any Schwartz books, but doesn't he advocate going right to the 2 x 12's at the lumber yard then ripping & using the outer 3-4" of vertical grain wood and trashing the middle of the board? (use area marked in red in pic)

268956

[John Crawford]

Hi Everyone:

Thanks for the great replies. I did try to select pieces that didn't contain pith...but I expect I got pieces that were still too wet.

Scott: Would a lumberyard really exchange lumber? Thanks for your detailed post. I should have been armed with a moisture meter; the few bucks I wasted here could have been spent on that! I probably should have gone into the garage first, then later into the basement....

[Mel Fulks]

John ,are you on the west coast? Here on east coast Douglas fir is mainly KD and dressed to save on transportation costs.

[Scott T Smith]

Hi Everyone:


Scott: Would a lumberyard really exchange lumber? .

You don't know until you ask....