Help with unwarping a poplar desktop

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Forum topic by JamezDee posted 06-28-2018 01:13 PM 1062 views 0 times favorited 11 replies Add to Favorites Watch
View JamezDee's profile


2 posts in 1130 days

06-28-2018 01:13 PM

Topic tags/keywords: poplar wood desk warping

Hi Lumberjocks,

I’m currently working on a desk, with a steel frame and a 8cm thick slab on poplar for the desktop.

The poplar was delivered about a week ago, after having dried somewhat whilst in the lumberyard. It still has bark on which won’t come off easy, so I imagine it’s still drying?

The slap is currently warped across its short side, so it does not sit flat on the steel frame. It’s not huge but approx 5-10mm.

I have placed the slab on it’s steel frame and screwed it down in the corners. I have also placed some weight on top in the hope that this will cause it to flatten out.

It is stored inside, in the sunlight.

Am I doing the right thing, or is there a better way of approaching the problem?



11 replies so far

View Kazooman's profile


1540 posts in 3114 days

#1 posted 06-28-2018 01:46 PM

A slab that think will take many years to air dry! The general rule of thumb is about a year an inch. Do you have any idea when it was cut? What if any drying did the lumberyard do? Was it sitting outside or was it indoors? My guess is that it is going to take a long, long time to acclimate to the room and get completely dry. How much warp you have in the end is unknown at this point. It might wrap more or flatten on its own.

You mention that you screwed the corners down (apparently to try forcing it flat). You MUST allow for movement in the wood even after it is “dry”. The piece will expand and contract across the width with changes in humidity. Any screws must be applied in a manner that will allow them to move with the slab. There are many ways to accomplish this. Having a slot on the metal leg for the screw as opposed to a simple hole is one way. Figure eight fasteners is another.

View jonah's profile


2136 posts in 4461 days

#2 posted 06-28-2018 02:29 PM

The amount of force wood can exert as it moves is frankly amazing. You’re only going to be able to prevent that with an incredibly beefy and stuff metal frame, and there’s no way your standard desk legs are going to be rigid and strong enough.

You’re far better off waiting for the slab to fully dry (see the post above), flatten it with a hand plane or wide belt sander, and then use it as a desk.

The alternative is to just allow it to warp and use it warped.

View LittleShaver's profile


768 posts in 1782 days

#3 posted 06-28-2018 03:14 PM

Looking at the picture, the slab is going to want to curl up toward the drier side. If your screws are not in elongated holes to allow the slab to expand and contract, you will have problems. You have a couple of options. Elongate the holes to allow the slab to move. Pull out the screws on one side (front or back). Pull all the crews and add two to the center-line at the ends.

My experience with poplar is that it wants to stay flat, you just need to allow it the time and space it needs to get there.

-- Sawdust Maker

View bondogaposis's profile


6000 posts in 3513 days

#4 posted 06-28-2018 04:15 PM

It still has bark on which won’t come off easy, so I imagine it’s still drying?

Tight bark is not an indicator of moisture, it just means the tree was harvested when it was dormant, winter. I would get it out of the sunlight. You want the slab to dry evenly on both sides by putting it in sunlight moisture will be driven off of the top side much faster than the bottom side, that can lead to a whole host of problems like cupping. It sounds like you have some twist, the best way to straighten that is with hand planes and winding sticks.

-- Bondo Gaposis

View gargey's profile


1013 posts in 1938 days

#5 posted 06-29-2018 11:38 AM

One part not mentioned by the others: As it dries it will shrink, and if it’s screwed firmly to the steel frame it won’t be allowed to shrink SO IT WILL CRACK.

You need it to dry and shrink, then to flatten it, then to fasten it with a method that allows it to expand and contract.

Sorry. Not what you wanted to hear. Wood is a pain in the ass in this way.

View Aj2's profile


3952 posts in 2960 days

#6 posted 06-29-2018 01:22 PM

A good way to warp a board is to set by a window. Or direct sun light the uneven heat from the sun will dry the wood too fast on one side.
I’m probably too late James is long gone by now.

-- Aj

View jonah's profile


2136 posts in 4461 days

#7 posted 06-29-2018 02:10 PM

On the one hand, I’m delighted that wood is a part of the current design style for a lot of furniture. On the other hand, it gives people warped (no pun intended) senses of what can and cannot be done with wood. Here’s hoping they stick around and learn something!

View JamezDee's profile


2 posts in 1130 days

#8 posted 06-29-2018 05:14 PM

Hey guys,

Thank you all very much for your answers.

Indeed, as Johan was saying, I am a novice with wood but forums like this can really accelerate the learning process.

What I can conclude from your responses is that I shouldn’t try to correct this deformation with force, but simply try to keep the wood out of the sun, allow it to dry naturally and see if the end form really needs to be reshaped.


View Aj2's profile


3952 posts in 2960 days

#9 posted 06-29-2018 06:34 PM

Yes you should let it dry slow and evenly.
We have a saying in woodworking go with the grain. This apply to much more then cutting wood.
Unfortunately many feel they can control or force Mother Nature to what they want. The craft becomes frustrating and they move on to other things. Golfing or drinking I guess

-- Aj

View JCamp's profile


1380 posts in 1713 days

#10 posted 06-29-2018 07:27 PM

I’m gonna throw this idea out here and you can take or leave it. In the end after it is dried if it is still warped one potential way to get it even would be to cut a lot of slots in the bottom side of the desk to allow you to “flex” the board back to flat. That would not be my first move and it’s more like hammering a square peg in a round hole but if it was between replacing that top and cutting the slats I’d make the cuts

-- Whatsoever thy hand findeth to do, do it with all thy might

View jonah's profile


2136 posts in 4461 days

#11 posted 06-29-2018 07:46 PM

James – indeed it’s basically impossible to force wood to do what you what it to do. It will naturally swell and shrink along all three dimensions (though much more side to side than the other two directions) with changes in temperature, humidity, and sometimes UV exposure.

You didn’t say how long the slab had been drying, when it was cut, or whether it was kiln dried at all. That’s going to be a big factor in determining how much longer you need to let it dry for.

Ideally, you want the wood to be somewhere below ~12% moisture content (MC) before you start working with it. That varies by location and species of wood, but is a good rule of thumb. As a basis for comparison, the “kiln dried” 2×4s at home depot are probably 22-25% MC. I put “kiln dried” in quotes there because they basically drop them in a kiln for a completely inadequate amount of time and then ship them out as “kiln dried”.

Once you get the slab dried appropriately, I’d see just how warped it is and then decide if you need to address it. It might be completely usable even twisted a little. If you do have to flatten it later, you’ll want a good sharp hand plane (if you do it yourself) or a wide belt sander (look for a millwork shop or specialty woodworking shop). As with anything, doing it yourself will be cheaper, much more difficult, much more effort, and yet much more satisfying.

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