Warped boards

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Forum topic by Marpel posted 02-04-2018 09:17 PM 808 views 0 times favorited 9 replies Add to Favorites Watch
View Marpel's profile


27 posts in 1067 days

02-04-2018 09:17 PM

I am in the process of building new kitchen cabinets (solid maple face frames and doors, pre-finished 3/4” maple plywood carcass). So far, have cut all plywood for upper and lower and have completed the upper cabinets/face frames. I cut and glued the upper doors (glass panels yet to be installed), but yet to apply finish. The lower plywood pieces are, as yet, unassembled. Because of other commitments, the whole thing has been on hold for the last few months. Just got back to it the other day.

The solid stock, finished 4 sides, was judiciously picked and I was lucky enough to be allowed to sort through quite a bit of stock to choose the choicest (knot and blemish free), straightest pieces. Purchased from same place as plywood.

Now to the issue: within days of cutting up all the plywood pieces, almost every one has showed some cupping/warping. As a result, I had to do some “tweaking” during assembly of the uppers and a couple of the sides (hidden by adjacent cabinets) still show about an 1/8” from straight. The, as yet assembled, lower carcasses exhibit cupping up to over 1/4”. The larger pieces can easily be forced back into shape, but the smaller ones are harder to accomplish.
The upper doors, which were also glued up a few months back, also show some warping. While one is only out by about a 1/16”, one is so bad, I have had to cut new pieces (yet to be assembled). Have also not cut up the face frame or doors pieces for the bottom cabinets.

So, a couple questions:
- I have never used pre-finished plywood, but am surprised all the plywood has cupped as bad as it has (bought from a plywood/wood outlet that is relatively climate controlled and stored inside my basement). Is this usual for the pre-finished stuff??
- When I cut the first batch of face frames and rails/stiles, I ripped a wider (by about 1/4 inch) board down to the finished dimension, and merely made a single cut. The latest doors I cut, I actually ripped a 1/8” piece then flipped it and cut off the rest from the other side (thinking cutting a bit off both sides would mitigate the warp). Does this latest method sound like it may help?? The face frame and rail/stile wood is also stored in the basement of my residence, so is reasonably climate controlled.
- Is it possible to “un-warp” wood??
- Lastly, is maple more prone to warping (have used ash, oak, poplar etc in past and have not experienced the same degree of warping)? And, any suggestions to control warping/cupping in the future??

Thanks in advance,

9 replies so far

View Manitario's profile


2816 posts in 3660 days

#1 posted 02-04-2018 09:49 PM

All wood moves; I’m not sure if maple is any better or worse than any other wood. Also not sure that prefinished plywood is more susceptible to warping than any other plywood (if you want hours of amusing reading, just google “should I finish both sides of my __”) I find the majority of my plywood warps over time after I’ve cut it, regardless of whether one side is finished or not. I find plywood often worse than solid wood for warping over time. Unless you have a perfectly climate and humidity controlled shop, exactly the same as the store, the moisture content change is going to cause it to warp.

I find with plywood, the best strategy is to leave it in sheet form as long as possible, until you are ready to cut and build. Breaking the sheet into smaller pieces and then leaving them for a couple of months is a sure way to come back to find them not flat anymore.

Solid wood is a bit different; I buy all my wood in rough form and try to let it acclimatize in my shop for several months before I use it. Then I mill it in stages; joint/plane to get it slightly oversized, leave it for another week and then come back and mill it flat again to final dimensions. Even then, if I cut some pieces and leave them for months, I find that they may not be flat or the joints may not be perfect (not that my joints are perfect anyways!) A well known woodworker online swears that if he cuts dovetails he’ll try to assemble the piece in the same day b/c if he waits, he may not find the pieces fit together properly anymore.

I’ve never had any success in flattening wood that’s warped. There are all sorts of methods you can try…but you’ll probably save time and frustration to just re-do the worst pieces.

-- Sometimes the creative process requires foul language. -- Charles Neil

View pintodeluxe's profile


6158 posts in 3591 days

#2 posted 02-05-2018 02:01 AM

Plywood doesn’t usually warp much for me. I agree about keeping it in sheet form until you’re ready to build, but it doesn’t always work that way.

Hardwood rails and stiles should be rough milled, then let them sit overnight. Then joint them flat again, and plane to finish dimensions. This extra step is particularly important for cabinet door parts, because they need to be flat without any additional support. Parts that will be glued in rabbets or dados don’t matter as much, because you can make them straighten out during assembly.

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

View Marpel's profile


27 posts in 1067 days

#3 posted 02-05-2018 02:40 AM

Manitario, pintodeluxe,

Thanks for your replies.
Was not intending on letting the pieces sit for so long, but due to unforeseen circumstances….

My initial comments may have not been perfectly clear, but the solid stock that has warped are 5 doors that had been assembled and glued up quite soon (within hours) after they were cut to size. They were then set aside, laid flat one on top of each other with 4 – 5 small sheets of plywood on top for some weight (although I did not intend the plywood to be weight against warping, it just turned out that’s the way I had stacked things). So they warped after glue up but prior to any finish. The couple that have warped, if laid flat one corner can be pressed down on the table and the opposite corner will lift up.
Unfortunately, I do not have a planer (am actually considering the Dewalt 735, but I also covet the brand new $4000 Nikon 70-200 lens!!) or jointer, so the wood was purchased already milled (correct thickness, but a bit wide), had sat at the store for a weekend prior to purchase, then sat in my basement for a few days prior to cutting to length and assembly. I still have a number of 8 foot or more boards that were purchased in that same order that are still perfectly straight.
Although I have experience with plywood panels, this was the first time I used pre-finished (pre-finished on both sides) and, as other plywood I have used has never warped (I have a few sheets of Baltic Birch that I have cut from large sheets that have sat around for up to a year with no noticeable warping). This was the reason I was wondering if maple, and in particular pre-finished maple plywood, has a tendency to warp more than other species. As well, I’ve always thought that plywood was well renowned for its resilience against warping (due to cross-grain layering).

Anyway, thanks again,


View WDHLT15's profile


1819 posts in 3253 days

#4 posted 02-05-2018 12:28 PM

I believe that you have a moisture content problem. Wood that is in equilibrium with its environment does not warp. Wood moves when it is losing or gaining moisture, so the warping is occurring because the wood is either losing or gaining moisture. Maybe your basement has high humidity.

Another thing, how you store wood is important. If you lay a piece of wood flat, and it is gaining or losing moisture, only one side is exposed to the moisture change. One side is gaining or losing moisture, the other is not . This leads to cupping or warping. Laying plywood flat is OK if you cover the top layer with other boards or other stuff to protect/cover the top exposed surface.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln.

View Robert's profile


3748 posts in 2258 days

#5 posted 02-05-2018 02:56 PM

Marv, I think there are several areas to address.

Basically wood moves due to 1) unequal drying and 2) internal stresses. Internal stresses develop as wood dries and it changes shape to equilibrate them. Each time you remove wood, it reprocesses itself.

1. Until wood is totally acclimated, you should always store your it stickered, never lay them flat on a surface because air will only affect one side and that side will dry unequally. The fact the wood warped means it was not totally acclimated.

I prefer to use the term acclimated rather than dry, because dry is relative to the environment. A flat table top in Brazil will probably have issues if moved to Arizona, and vice versa.

Another problem you will encounter is after moving a project inside a house from a shop is movement will continue. So in a way you a lucky this happened before you installed the doors. For example, wood may be acclimated at 12% in the shop and re-acclimate to 8% inside a house (fairly quickly, I might add).

I strongly recommend storing your project lumber inside the house or in a climate controlled room for several weeks before milling even begins. This has alleviated many headaches for me.

2. Always mill your stock incrementally, never remove material to final dimensions in one cut. This applies both to jointing/surface planing as well as ripping to width. The basic rule is “whatever you do to one side you do the the other”. You were correct to rip the stiles to width off both sides.

3. Warped doors can be straightened by a technique called “splining”. I learned this from Charles Neil. He demonstrates it in the pie safe video. Basically you cut a deep groove, clamp the doors to a flat surface and glue in a spline with a hard drying glue such as epoxy or resin glue.

4. FWIW, I never buy kiln dried surfaced lumber from suppliers anymore unless absolutely necessary. The problems with this lumber is a) rapid kiln drying induces stresses and b) the wood is often 13/16” & you don’t have enough material to work with to mill out a defect. I buy direct from a sawmill and season the wood myself in a drying shed. Since I started doing this I have much better luck.

5. Plywood will warp if not stored right. For me, this means flat and horizontal. If you have a cart or rack, you can store it vertically. It is not hearly as affected by changes in humidity like solid wood.

6. Think about your shop & your climate especially humidity fluctuations because this is the source of all problems related to wood movement.

Hope this helps. Don’t mean to be long, but what you are experiencing is crucial aspect to ww’ing that causes a lot of frustration.

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

View Marpel's profile


27 posts in 1067 days

#6 posted 02-06-2018 03:00 AM

Thanks everyone for taking the time to respond. Much appreciated.

A lot of good (and new to me) info. Gives me something to think about as I start cutting and assembling the lower face frame and doors.


View AlaskaGuy's profile


5812 posts in 3087 days

#7 posted 02-06-2018 03:36 AM

As already stated all wood even plywood can warp if you get an imbalance from one side to the other. Keep you cabinet box cut pieces stacked and cover the top piece, or spread the pieces out so all side get air movement.

He’s an example of what can happen when you don’t cover the top piece to keep the air form both sides.

-- Alaskan's for Global warming!

View AxkMan's profile


65 posts in 904 days

#8 posted 02-06-2018 05:50 AM

Try using a moisture meter to check the wood. If there is a lot of moisture then most likely this is your problem. You might want to consider leaving them covered with a tarp in the future. Constant outside exposure could be a culprit.

A method you can consider is clamping the wood on a solid surface and leaving for a few weeks. This sometimes works for me on boards. You have to consider it may just warp what it is clamped to however.

You can try clamping a solid surface to it to see if that helps as well if it is already glued.

View MrRon's profile


5913 posts in 4021 days

#9 posted 02-06-2018 10:08 PM

I believe that some plywood may have maple on the face side and a different species on the other side. That could cause warping due to differential amounts of stress relief.

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