How to Flatten A Solid Wood Panel that has Cupped or Warped | Woodworking

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ABOUT
Sometimes even kiln dried hardwood panels can cup in the right (or wrong) circumstances. Here, I explain why this can sometimes happen, and show you a simple method for correcting a cupped panel.
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CHAPTERS
00:00 Why Did My Panel Cup Like That?
02:32 How to Flatten a Cupped Panel
04:44 Outro
#woodworking #hardwood #panels #cuppedpanel #woodshop #woodwork #woodworker

[@youngun1496]

Hi, I was skeptical but decided to try your technique. Sure enough the board flattened overnight. Saved my commission. Thanks!

[@sturdyboneswoodworking]

Amazing! Love to hear that!

[@nikolashull8727]

So excited to try this, making a father's day gift and of course out of all of the wood we have the perfect piece for my project is cupped. Thank you for the advice!!

[@sturdyboneswoodworking]

Very cool you’re making something for Fathers Day. I hope it works well for you!

[@MMMS75]

Great tip! Wish I found this video last month when I had the same exact problem. Now I know. Thanks!

[@sturdyboneswoodworking]

Thanks hope it works out!

[@th34lch3m1st]

Great tip, will definitely come in handy when needed. Thanks for sharing.

[@sturdyboneswoodworking]

Awesome. Thanks for watching and hope it helps you at some point!

[@tfmrotek]

I can definitely say I learned something and this fix will undoubtedly come in handy!

[@sturdyboneswoodworking]

Awesome! Hope it helps!

[@GlennMartinPhotography]

Solid advice. Looking forward to more of your work!

[@sturdyboneswoodworking]

Thanks Glenn! 🙌

[@ckutzli]

Nice video, good luck with your new adventure

[@sturdyboneswoodworking]

Thanks so much! It’s been a wild ride already. Can’t wait to get the next one done.

[@jonbryant3784]

I stumbled across your channel this morning - in fact, it came up 2nd in my feed. Nice job. I subscribed and look forward to watching your channel and business grow.

[@sturdyboneswoodworking]

Thanks for watching and subscribing, Jon! There is a lot more to come! They won’t all be this format but as I feel I have more informational things to share, I’ll occasionally get in front of the camera and talk. I’m most excited about my upcoming build ideas. What did you like most of what you saw?

[@jonbryant3784]

I look forward to the upcoming build videos. I like a mix of tips (like this one) and interesting builds. My wife and I recently launched a custom furniture business focusing on outdoor furniture, so we’re on a similar path as you and will enjoy following your success. We also just purchased 60 bf of beautiful black walnut for a piece we’re building for ourselves so that’s what attracted me to this video - we’ve been worried the 17 inch wide boards could cup while they are acclimating. I had never seen your technique and I’m feeling a lot better. All the best to you.

[@sturdyboneswoodworking]

Awesome yeah it’s absolutely an adventure for sure. I’d be nervous about 17” wide boards too. But yeah if you sticker them all the time they should be okay. Best of luck to you!

[@bobgaines2399]

Thanks so much for explaining, in easy terms, how to fix this problem. I will definitely be using this method and checking the moisture content of my lumber before I begin the milling process and after. I hope the best for you brother, I just subscribed

[@sturdyboneswoodworking]

Hey so glad this was helpful. Yes, it’s definitely best to start by getting it right the first time with sufficiently dry material and let it rest a bit after milling. Even better if your shop is climate controlled and/or has a dehumidifier. I run a dehumidifier constantly because my shop is not climate controlled and I think it helps limit movement in pieces just because the weather outside is wild.

[@stlwoodworking]

Great job with the video man.

[@sturdyboneswoodworking]

Hey thanks so much!

[@adamvincent2150]

Trying this now to save a small table build. Hope it works as well for me as it did for you!

[@sturdyboneswoodworking]

Awesome! I hope it goes well too! Let me know if you have other questions!

[@JesperMakes]

Nice 👍

[@sturdyboneswoodworking]

Thanks Jesper!

[@jasonstevenson8569]

Great video. Love it

[@sturdyboneswoodworking]

Glad you enjoyed it. Thanks for watching!

[@1deerndingo]

Nice video. Good info. Nice style. Subscribed.

[@sturdyboneswoodworking]

Thanks! I’ll keep that in mind next time I have a tip to share!

[@beaujolaiswright8386]

Fantastic video, thank you!

[@sturdyboneswoodworking]

Thanks for watching!

[@walterrider9600]

thank you

[@sturdyboneswoodworking]

Thank you, my friend! I hope it helps you!

[@saw-sound]

Man!tha was extremly usefull!well done bro!

[@sturdyboneswoodworking]

Did it work for you?

[@kaceystevens6198]

Cool to see how fast it works

[@sturdyboneswoodworking]

Yah, blew my mind too. I thought it would take way longer than 3hrs

[@twoweary]

It seems to me that if you live in an area that rarely, if ever sees 10% humidity ( like the PNC where I live), if you kiln dry your wood it’s gonna start moving as it acclimates to higher humidity after it leaves the kiln. I have a cutting board that’s at least 5 years old that just recently started to cup. I’ll give your method a try. Thanks for posting.

[@sturdyboneswoodworking]

Yeah the good news is that you don’t need your material to be super dry, just at equilibrium with your shop and really with the final place the piece will live, which is usually indoors (though I realize not all regions have A/C). But I could see how a cutting board might suffer if it’s being washed regularly and not well sealed with an oil and/or wax.

[@miked1050]

Wish I had found this video a year ago when my first project cupped like crazy from my summer humidity!

[@sturdyboneswoodworking]

I wish I had made it a year ago! 🤣 sorry you had that trouble. Hopefully it helps in the future.

[@Robinkoeleman]

Exactly the video I needed! Made a furniture out of solid white oak and glued some panels for the doors. It has been some months now and the customer sent me a message that the doors started cupping a lot. Looks like I’m going to try this trick to see if I can make the doors flat again. Only thing I’m wondering is if the panels stay flat after this procedure or if there is a chance they will start cupping again. I’m curious about your experience! Great content, going to subscribe 👍🏼

[@sturdyboneswoodworking]

Hey thanks so much! I hope this works. There’s a chance if you’ve already put finish on them that they might still cup on you or not flatten out with this trick. It depends on the fibers in the wood absorbing some moisture back in and then releasing again hopefully more evenly. I’d guess the reason your doors cupped was due to the inside face not receiving the same airflow as the outside, causing them to cup outward. This is the best case for making sure your stock is kiln dried before making panels. In my case I was also using air dried wood and while it read around 12% before use, my shop midsummer can still get pretty stuffy. I still use that table in my house and while it’s not perfectly flat, it’s nowhere near as bad as it was in this video.

[@kristaheffley2419]

Great fix! Thanks for sharing. Any idea how to prevent the cupping from happening again when it's on an RV table that has legs attached? I'm not sure if I can, or should, reinforce it some how so it doesn't continue to cup as the weather changes. Thanks!

[@sturdyboneswoodworking]

If the panel cupped after glue up due to temporarily leaving it with one side unable to breathe, it shouldn’t happen again if you allow it to dry again evenly after wetting one side and allowing it to flatten out. For something like an RV table that won’t be climate controlled all the time, I’d consider adding breadboard ends which should help mechanically keep it flat. I have a video about breadboard ends on my channel you could check out as well: kzbin.info/www/bejne/eofSe4OHmdqDe7csi=2LegySduHGU8lgEf

[@levibeselt2068]

Trying this as I am writing this comment, I will update in a couple hours how it went👍👍

[@sturdyboneswoodworking]

💪🏼💪🏼💪🏼

[@timgreig7474]

Great video! Thank you! I have a 100 year old piano bench with a solid wood seating top that is finished in whatever finish they used back then. Over time the top has cupped from being sat on by too many fat ... you know. Do you think your method would work for a finished board? I'm not too concerned for what happens with the finish since the rest of the bench and piano's finish need a significant amount of TLC, and some day I'll give it some lovin' with Howard's RestoraFinish. Again, thanks for the vid! Great work!

[@sturdyboneswoodworking]

Hi thank you for watching! And yeah those fat kitty cats can really do a number on a piano bench. 🤣 I think if it has a film finish on it this method won’t work great. Wood will move most when it’s first drying out, and after it has been freshly planed or sanded. If a panel has cupped because it basically has been stressed out of square like from constant pressure from a clamp (or a kitty cat sitting on it for long periods), it’s likely that the fibers have permanently settled in that position and this method won’t work. But beyond that it sounds like just restoring the piano bench altogether would be appropriate.

[@timgreig7474]

Darn! Thank you once again for the video and now the advice for piano bench!

[@bobgaines2399]

what's the better way to store lumber when you bring it home from the lumber yard? I know humidities will change between the store and my shop, and may be several days before I actually begin the project. I've heard stand it up, lay it flat, lay it flat and put weight on it, etc. What's your take on it, and how do you do it?

[@sturdyboneswoodworking]

Definitely lay it flat and preferably with “stickers” between the boards. Stickers are just small strips of wood or plywood all the same thickness you can space out and layer between the boards. That will allow airflow all around the boards as the material acclimates to your shop. I have a couple lumber racks along the walls shop and that’s my preferred place to stack it. Thanks for watching!

[@eitantal726]

Will the flatness last, though? I ask because, while you *can* manipulate expansion with water, the water itself will seek equilibrium on its own. I watched a video where it was attempted to flatten rough lumber using the same process. It did not last.

[@sturdyboneswoodworking]

Yeah that’s a great point. I can’t speak to the rough lumber instance because how wood initially dries out from green to ~20% does a lot to establish what shape it’s going to take. That’s why you have to sticker it as soon as it’s milled. But if your lumber is air dried or kiln dried and cups after being glued into a panel like this, and if it is handled properly until it can be secured flat to a table, the chances are pretty good. I wouldn’t claim that my coffee table top is perfectly flat but it’s definitely not out by 3/16” like it was in the video. So it’s fair to say this is not a perfect solution but a decent one and a good thing to try if your alternative is to scrap your cupped panel.

[@PriceyBuilt]

Great video. Subb'ed and looking forward to what else you do. May I suggest checking your audio levels across the video. The voice over is much quieter than the talking head sections.

[@sturdyboneswoodworking]

Hey thanks for that feedback! I will keep that in mind next time.

[@natepostill]

Liked and subscribed

[@sturdyboneswoodworking]

Thank you!!

[@petec6690]

I've bought beautifully flat plywood panels then stacked them agains the wall (not flat against). Next day it has a bow. I thought plywood is supposed to be flat and stable? Why are my panels moving? What can I do to remedy both their moving AND after they've moved, how do I return them to flat?

[@twoweary]

Probably a good idea to lay them flat on top of some stickers. Especially if you’re not planning on using them for a while. Perhaps even with some weight on top.

[@sturdyboneswoodworking]

Plywood is a much different story than solid wood. It’s still wood but the grain of each ply runs opposite to each other which is why it’s regarded as more stable. I’m not positive this method will help with that. I usually only see distortion on plywood when it’s in a full sheet form and usually it’s due to it leaning in such a way that it’s holding a bend for a while without moving. So it think that’s a micro version of the effect that steam bending has where eventually the fibers start to just settle into their new shape instead of resisting.

[@dmacko]

Once you do this and the panel returns flat, how do you keep it from cupping again? I ask because I made a noodle board in my garage and when I brought it inside, less than 8 hours later the panel cupped. I live along the southern coast of Oregon and it's currently rainy season, so lots of moisture in the air.

[@sturdyboneswoodworking]

Sounds like you have a pretty high differential between your outdoor relative humidity and indoor. I would try clamping it to something really flat after you get it flat in the shop and keeping it clamped indoors for a few days. There’s a chance it will stay flat if it’s allowed to acclimate to your indoor humidity while clamped.

[@plokamias_]

Great video! Question tho… when the wood becomes dry again wouldn’t it reverse to its old curvy shape?

[@sturdyboneswoodworking]

If it was allowed to dry evenly on a flat set of stickers, it will not necessarily return to its cupped form. Keep in mind the scenario I’m suggesting this method for is specifically when the panel was prevented from experiencing air flow evenly on both sides. That is the condition that encourages cupping toward one side. I don’t suggest this method will work for every case but in mine, the top panel is still fairly flat.

[@plokamias_]

@@sturdyboneswoodworking Thanks a lot! I was also curious if this works for curving the panel in both x and y axons but I guess it has to do with the wood grain. I will try it myself soon. Cheers!

[@augustwest8559]

I don’t worry too much about thin panels bowing. It’s easy to bend them in a frame of a table base like yours. It is a good experiment too see how much wood moves.

[@sturdyboneswoodworking]

Yeah I could see situations where it’s not that big of a deal. Like if this panel had cupped toward the bottom side, it would have probably been okay to just clamp it to the base and hold it there with maybe an extra z-clip and over time it might just stay that way. It’s harder to let it go if it’s the outer edges flaring upward like this panel was suffering from.

[@jeffreyflasch5338]

I built a live edge table that is 1 1/2 inches thick & after several months the same exact thing happened! :( Will this idea work on thicker material?

[@sturdyboneswoodworking]

That’s a great question. It will work but I couldn’t say whether it would remain flat long term afterwards and you’d have to be more extreme on how wet you make the concave side. I had a client build a bartop from 2” thick green slabs I sold him despite many warnings that cupping could be an issue and it definitely did cup up on him. He had to leave soaking wet towels on it to get it to relax. I’d also recommend doing any maintenance with the panel detached from the table and if you get it flat again with something that thick, absolutely strap it down with cauls while you let it dry for a while so it doesn’t potato chip up on you right away. Results will also vary if your tabletop has already been sealed with any finish. In my example I had not put any finish on the panel so moisture could move much more freely.

[@luketobia7548]

Do you think this method would work with any size panel? I wonder if you could just wet the wood directly on the cupped side for a much larger panel if this would still work?

[@sturdyboneswoodworking]

It will work but will take much more water and it absolutely needs to be able to dry evenly once it’s back in a flat condition. For thicker tops or slabs it’s possible they will never really recover if the cupping is bad. This method is really meant more for a triage step to try before scrapping and starting over, and only as a remedy for the conditions I describe where it was dead flat and cupped after the panel was glued up.

[@ferhatcevik8307]

It turned out very nice, but is this valid for an oiled and finished table because oil will not absorb water, how can we do it then?

[@sturdyboneswoodworking]

I think it would not work as well. It would depend on what sort of oil was used and whether it had fully cured. This method depends on the woods tendency to cup toward the dry side so it’s encouraging the convex side to be the dry side and not allowing the concave to dry as quickly. If the oil has totally sealed the wood grain such that no moisture can move through the surface, it may not work.

[@MarinerG]

Is that method work with thicker tops, like 30mm? And are we sure that this thing will not bend again?

[@sturdyboneswoodworking]

The idea is to get it to lay flat again on its own and then secure it in place to the base before it can move again. Since attaching panels to a base (in case of a top) is usually one of the last things you do during assembly, Id also suggest that the next thing is to get it into a climate controlled environment where the humidity will also change less than in a non-controlled shop. If you do those things, the combination of those elements will probably keep it flat even if its tendency would be to move again. As for the thickness, I just did this again with a top that was over 30mm and it worked great. Just takes longer.

[@MehrabS]

Will this method work with a large slab?

[@sturdyboneswoodworking]

Most likely this will not work on a large slab. For one you’d have to get it much wetter than just a damp towel. Second, if you were able to get the fibers wet enough to relax in a big thick slab, you would have to have a plan to clamp it flat and allow air to flow around it until it dried evenly, and even then, it might return to its cupped or warped shape. For large slabs the best way to get them flat, assuming they’re rough and have enough thickness, is to flatten it with a router sled and spoil bit.

[@alexgarcia-ug9zk]

does this work when the sagging is due to the gravity? i made a table with improper support, i'm hoping to fix it but the tabletop is a bit sagged in the middle.

[@sturdyboneswoodworking]

It’s possible but in general I’d say this method is for unfinished panels. When we apply oils, paints, or varnishes to wood, it fills the pores in the wood making it less likely that wetting down the material will allow it to flatten back out.

[@alexgarcia-ug9zk]

@@sturdyboneswoodworking oh yeah! it's unfinished wood, i forgot to mention :)

[@TomHull-p9d]

Will this work if the wood has already been varnished?

[@sturdyboneswoodworking]

It probably will not work because at that point the pores have been closed up and the wood is not going to take in much moisture when you place it on the wet towel.

[@skrachi1986]

Will this work with MDF?

[@sturdyboneswoodworking]

I’m afraid not. MDF would swell up and likely never return to its original thickness when exposed to that much water. I don’t recommend it.

[@gototcm]

What happens a few days later when the wood dries out? Is it warped again?

[@sturdyboneswoodworking]

Not if you let it dry evenly on both sides. I explained in the video that the reason boards and especially panels cup toward one side has to do with it drying unevenly on both sides and that in my example case, I had allowed it to rest on my assembly table without stickering it. Once I fixed it using the method in the video, I stickered it and allowed it to dry evenly and it still hasn’t cupped back like that.

[@haydenstacpoole7987]

I like

[@sturdyboneswoodworking]

Thanks!

[@Rich32262]

I see how this would work if you stored your lumber with one side exposed and the other against a wall, board, etc. which would let one side dry more than the other. I'm curious how it would work if the boards had been stored properly. They would absorb the moisture, but I would imagine in many cases go back to the curve once they dry out again. If that happened I wonder if you could repeat the process, once flat, apply a water based finish and a top coat to seal in the moisture. Totally speculation on my part.

[@sturdyboneswoodworking]

I think you're on the right track. Even applying film finishes doesn't completely halt wood movement, but it does change the rate at which the wood absorbs and releases moisture. That's why you'll frequently see advice about always finishing all sides of a piece, and particularly both top and bottom of large panels. What you're looking for is to slow down the rate of change to almost a complete stop, and to ensure that as it changes over time, it is set up to do so **evenly**. So yeah that's why its bad to let one side be face down or against a wall while the other faces an open room. I didn't mention it, but in one of my other videos, I made sliding doors and had some massive cupping problems with the doors getting stuck because they got wedged in the track. They wouldn't budge open or closed. We had had a ton of rain and the inner face was able to get drier than the outer, which was exposed to the RH of my shop. My dehumidifier couldn't keep up with 3 days of rain. The solution was to move the dehumidifier to sit three feet away from the cabinet, and the doors relaxed. My mom owns that cabinet and she has not had any more issues with the doors now that the cabinet is in a climate controlled environment in her house. So that's anecdotal evidence, but it tells me that if it's flat to start with and moves, when it returns it won't bend back after it's fixed.

[@eitantal726]

had the same problem, but instead of using a damp towel, I just wetted the concave side. It made the cupping worse

[@sturdyboneswoodworking]

Shoot. I guess maybe by introducing a lot of water and (guessing here) letting it dry in the open, it triggered a lot of evaporation on that side which by the time you interrupted the evaporation had allowed it to pull even more water from that side. The method I demonstrated here encourages the evaporation and water loss to come from the convex side which makes it bend back. Sorry you had a bad experience.

[@CivicWaterboy]

I also added some water right onto the wood (convex side), only to realize I made a mistake = towel touching convex side. Should I be adding water on the other side?

[@eitantal726]

@@CivicWaterboy I saw a tip elsewhere about the use of a clothes iron: Damp towel + hot iron on the concave side

[@CivicWaterboy]

I ended up flipping the panel over and repeating the process = it worked!

[@tams1867]

⁠@@CivicWaterboyso when you flipped it over and had the concave ( boat shaped?) facing up? Then you sprayed that side? I’m having a major problem with a bowed butcher block vanity top.

[@1lapmagic]

Wouldn't the panel just cup back again when humidity normalized to the environment?

[@sturdyboneswoodworking]

Thanks for watching. It won’t necessarily if it is allowed to dry evenly on both sides. This won’t work with every panel. For example if it was glued up with edges that weren’t square for example, this won’t fix it. My coffee table top is still flat. It helps that I’ve attached it to my base and it acclimated to AC life while secured in place.

[@jakemoran6058]

will it not just return to being warped once its dry again?

[@sturdyboneswoodworking]

It could still move again but chances are if it was originally flat and only moved due to unequal drying rates on different sides, it may stay fairly flat. My coffee table top was allowed to dry evenly and was then attached to the base with Z-clips and it is still pretty flat now.

[@jakemoran6058]

I have a 132x32mm plank that is kinda warped on both sides at opposite ends. Do you reckon wrapping it completely in a wet towel would even it out?

[@DarrellWeavercom]

Going to try this with a table I accidentally cupped.

[@sturdyboneswoodworking]

Awesome! Let me know how it goes!

[@jonsutcliffe8508]

You went away for a weekend and left the Aircon running 😮

[@sturdyboneswoodworking]

Yeah dumb mistake. I usually turn my window units off just to preserve electricity but was rushing out the door last minute I’m sure. Thanks for watching!

[@sergeyivanov5733]

Не самый лучший способ выровнять панель с помощью воды. Лишняя влага дереву ни к чему. Я бы разрезал и переклеил по новому. Ещё очень часто гнёт дерево из-за напряжений внутренних, потому что плохо изначально было высушена.

[@sturdyboneswoodworking]

Right in some cases it can’t be saved and this technique won’t work. But there are some cases like the one I demonstrated where you can’t afford to make the panel any narrower by cutting it several times and reducing the width by 2-3 blade kerfs. And in those cases this is a good method to try first.