warping/cupping on oak panels

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Forum topic by MattEffinCameron posted 01-12-2017 05:20 PM 540 views 0 times favorited 3 replies Add to Favorites Watch
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10 posts in 684 days

01-12-2017 05:20 PM

I am edge joining some oak board for a project.

I have two panels, each ~2’ long, made up of 5 3/4”x5” oak boards
I have one 7’ long panel made up of 3 3/4”x5.5” boards
I then will have one 11’ long panel, made up of a number of staggered oak boarks (3/4”x5”)

The two shorter panels are the tops to tall cabinets in a built-in. I have made both of them…one I made to the wrong length, so I have also made a third.

In each instance, I use biscuits and glue to join the boards. I have not used cauls, but for two of the panels I had 3 pipe clamps underneath (with the panel resting on the pipe) and two on the top (between the bottom clamps). And for each of those, when it came out of the clamps, and for the subsequent days…the panels looked great. I then moved the panels from the workshop to the room at my house where they will be used, and 24-48 hours later when I go back to test fit them….they are warped. One had a sort of uneven warping but the other was one long gradual cup.

I did some reading on the forums and found that excessive clamp pressure might have been the issue. So when we did the third panel….I only used 3 clamps (2 on bottom, one on top) and I, just for the heck of it, also used bar clamps to clamp down on each end of each board where it met the next board in the panel…this was because although planed to the same thickness, aligned with biscuits, and reasonably straight…there was some very slight curving over the length of a couple of the boards and I thought by ensuring the boards were glued flat, it would save me time with sanding.

That third panel came out, looked excellent….I brought it to my house that night, and then the next day looked and it was cupped.

One of the other common causes for this seems to be moisture related but I just have a hard time buying that…tell me if I am wrong

These boards were rough cut 1” lumber used to line the stall of a barn on my property. They have probably been in place for the life of the barn which is about 10-12 years. There have been no horses in the barn (or any livestock) for the last 3+ years. There is no moisture in the barn….It is not weather sealed, and some snow can blow in…but the inside never gets wet or damp and I am sure any moisture that does make its way in dries quickly because the wind also passes through (and we have considerable wind).

The work to joint and plane these boards was completed in the barn, on a cold (and dry) december day. The wood remained in the barn for anywhere from a day to a few weeks after being prepped (depending on the piece) and was then moved to my father’s basement to be assembled/worked with. The basement is again, notoriously dry….they have an antiques business and have stored antiques in the main part of the basement for decades without ever having an issue with moisture. They dont have a sump pump, have never had any moisture in the basement at all, and run a dehumidifier in the summer to keep it dry (not that that matters since we have done all this work in the last 2 months anyway). The basement is also heated by a wood stove which ensures even moreso the dry air. (point is, I know some basements are damp, I dont think this one is)

Once completed, the panels were brought 5 minutes away to my house and put in the newly finished bonus room over our garage. The room has a ductless minisplit keeping it at about 70 degrees and, I think, quite dry.

So it seems unlikely to me, that given how long these board have been nailed to framing in the barn, and the dry environments where they have been processed, assembled, and will ultimately be sued, that moisture is the culprit…but who knows.

Interested in your thoughts as I am now nervous about bringing my 7’ panel to the house. Although the shorter 2’ panels are tops to cabinets and can be screwed down (and should work fine), the 7’ is a floating shelf which I really didnt want ot have anything underneath (so there wouldnt be any frame to keep it flat)....

I also read in another thread about this topic where the book Underwstanding Wood was repeatedly recommended to gain greater understanding of the movement and affects of moisture on wood…well I ordered the book and it just arrived….but as I expected it looks like I will need to read and understand quite a bit before I am in a position to apply that knowledge successfully to my project/problem :)

3 replies so far

View rwe2156's profile


3094 posts in 1629 days

#1 posted 01-12-2017 07:08 PM

We’ve all been there :-) Its usually related to unequal moisture but can also be related to stresses released during milling (less common).

1. Jointed edges have to be square or complement each other to create 90 degrees. When jointing I always run opposite faces against the fence to cancel out any error in the jointer itself. Even a minor error will be multiplied by how many boards are in the glue up.

2. Unequal drying/improper storage. The humidity could have been quite different from place to place you would have to measure it to see.

3. The problem could be the lumber itself. I would have doubts whether exterior lumber on a barn would be dry enough and/or acclimatized enough. I would say the lumber would have to be stickered for at least a few months prior to use. You would have to use a moisture meter to determine this.

Here are a few suggestions that have worked for me:

1. Be sure I have marked my panel prior to glue up so when jointing I can be sure about “face in/face out” to the fence. I use chalk because it is readily visible.

2. When the panel comes out of clamps, I immediately sticker and clamp the long edges together and allow to acclimate for a few days.

3. If the panel will be sitting around before installing in the project, I store the panel in a sealed plastic bag or wrap in stretch plastic wrap.

On the remaining 7’ panel I would clamp the panel between two flat boards with stickers and store it in your house for 2-3 weeks.

Although I have never owned one, I think a moisture meter can

-- Everything is a prototype thats why its one of a kind!!

View WhyMe's profile


1053 posts in 1710 days

#2 posted 01-12-2017 07:21 PM

A minor change in moisture can cause the boards to twist depending on how the boards were cut as far as how the grain runs . I like to use boards that are closer to quarter sawn because plain sawn can cause more warping. Going from an unconditioned space to a conditioned space will have a difference in moisture even if you don’t notice it.

View pintodeluxe's profile


5758 posts in 2962 days

#3 posted 01-12-2017 09:06 PM

My thoughts in addition to the excellent comments already posted.
1. Barn lumber is not dry. It can be 12-18% moisture content depending on your region.
2. Lumber for indoor projects needs to be kiln dried. Not just to prevent warping, but to kill bugs.
3. Plain sawn lumber will cup more than rift or quartersawn lumber.
4. Hardwood vs. softwood. I’ve never met a softwood without some tendency to warp or cup. To remind yourself of this fact, just sort through a stack of studs at your local building center.
5. Removing more lumber from one face than the other face will cause boards to distort. This is very common with barn lumber where one rustic face is desired.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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