Why did it warp and how to avoid it?

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Forum topic by justinwacker posted 07-20-2016 07:10 PM 1542 views 0 times favorited 20 replies Add to Favorites Watch
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4 posts in 854 days

07-20-2016 07:10 PM

Hey, guys.

Been lurking around here reading threads for years when I have questions but today I have a question specific to a project I did.

I built this ‘rustic’ ‘farmhouse’ style dining table about 1.5 years ago. After about a year I noticed this slight warping of the boards. Its not bad enough to scrap by any means but I’d like to avoid it on future projects of similar stature.

It’s all pine. Joinery for top is about a million pocket hole screws on the bottom. My shop is limited—biscuits weren’t an option and I didn’t think straight glue would be sufficient due to size.

I alternated grain direction. up, down, up down. The top is finished but bottom is not.

If I had painted/stained the bottom could I have avoided this by making it dry more evenly over time? Different joinery? More expensive species of wood?

Here’s some pics.

20 replies so far

View DirtyMike's profile


637 posts in 1080 days

#1 posted 07-20-2016 07:21 PM

was the lumber kiln dried? pocket screws huh?

View Aj2's profile


1814 posts in 1976 days

#2 posted 07-20-2016 07:33 PM

Looks like a top that wasn’t allowed to expand and contract.
Now the wood is trying to crawl away like a caterpillar. :)


-- Aj

View ChefHDAN's profile


1149 posts in 3028 days

#3 posted 07-20-2016 07:46 PM

There are some far better than I to answer the specific reason, but having this happen to a project is why I oversize the holes in cleats/trestles that I attach tops to so that there is about 1/16” on each side of the hole and always put finish on all sides of a project. Might just be 2 quick coats on the bottom but at minimum I don’t want an open surface to absorb moisture and cause cupping, bowing, or twisting.

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

View FLBert's profile


70 posts in 915 days

#4 posted 07-20-2016 07:49 PM


Its hard to tell but how did you join the top to the base. If you glued/screwed at multiple points it won’t allow for wood movement. If you attached at a center point then used either enlongated holes/washers, etc then that’s probably not it.

I would think that not finishing the bottom could be partially to blame too. If the wood is sealed on top but not the bottom the rate that it takes in moisture can be causing you issues.

-- Bert, Lake City, FL

View rwe2156's profile


3144 posts in 1659 days

#5 posted 07-20-2016 08:40 PM

Lots going on here.

Basically what has happened here is one of two things (or a combination of both): The wood has continued to dry out and/or the wood is attached to the base in such a way as to constrict movement. Another factor are natural stresses in the wood become more evident as it dries. Any of all of this has resulted in the cupping you see. You have a pretty severe twist there, too.

1. Due to the prolific knots, this looks like 2×4 SYP boards which is construction grade lumber, and consequently full of moisture. Even if they say “kiln dried” the moisture content will be very high due to the way they store it.

But that doesn’t mean they can’t be used for furniture, you just can’t use it right away. The lumber has to be allowed to dry and acclimate to the environment in your shop (which hopefully is similar to your house). This is done by stickering the boards and giving them a month or so. Check periodically with a moisture meter or by simply weighing the boards and recording the weights right on the board. When the weight loss has stabilized, then the wood is ready.

So this ^ was probably your first “mistake” but it happens to all of us, even in the best of circumstances.

2. Unless I’m reading the pic wrong, you have too much unsupported board on each side. The apron should extend to within about 2” of the edge of the board.

3. The next factor is using wide boards for a table top. Even if the lumber is dried and flat at the time of assembly, the wider the board, the more it will move. In the future you can avoid this by using 4-6” wide boards. If the material is wide, I recommend ripping it down and rejointing prior to glue up.

4. IME I haven’t found coating both sides of a board will eliminate cupping, although it is recommended AFTER the wood has reached equilibrium.

5. Fastening a top in such as to constrain a board is a no no. I don’t know exactly how you did it, but there are several fastening techniques and hardware such as figure 8 fasteners or clips that allow the wood to move and not crack or bend.

6. Finally, using pocket screws the way you did may have been the only way you think you could have joined them, but actually a simple butt glued joint would have worked fine. If you don’t have clamps, there are cleat and wedge systems very easy to make that will accomplish the same thing. Even tie down ratchet clamps and cauls can be used.

7. Finally, a breadboard end will help, but not with major cupping like you have here.

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

View pintodeluxe's profile


5788 posts in 2991 days

#6 posted 07-20-2016 08:57 PM

Using quartersawn lumber will help with future projects.

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

View TheFridge's profile


10515 posts in 1664 days

#7 posted 07-20-2016 09:26 PM

Ana White?

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Logan Windram's profile

Logan Windram

347 posts in 2640 days

#8 posted 07-21-2016 12:18 AM

Construction grade , plain sawn 2 X 10 lumber of high moisture content got put together flat then went crazy when it dried out…

I like that look, nicely done. I’d consider doing that table top again in kiln dried Ash that has been stored inside for a while. Start 8/4 mill flat about 1/4 for desired dimension, then sticker/ stackfor a bit… Them mill to final thickness. You’ll have much better luck.

Ash in inexpensive, hard, and would great with that pickling. Don’t rush the drying or milling, or the wood will teach you a lesson in patience!

View dbray45's profile


3320 posts in 2955 days

#9 posted 07-21-2016 12:07 PM

These answers are mostly correct but I am not seeing one answer that is the key.

Look at the end grain of the boards. The board on the right – the center of the tree is top dead center (where the crest of the bow is). The third board from the right, – center of the tree is on the top to the right of center (again, crest of the bow).

The center of the tree does not hold a lot of moisture and the grain is tight but as the tree grows can hold a lot of stress. As you move away from the center, the moisture gets higher but the grain is still fairly tight so drying it is more difficult. When the moisture starts to leave, it moves in the way you see due to shrinkage.

And now you know why they DON’T dry the wood as much as they should, you lose a lot in dimension and more waste. Watch the grain when you buy the wood, this is good fence material.

Oh, and I have 20” wide boards that do not bow like this because I watch the grain and I dry it carefully.

-- David in Damascus, MD

View bondogaposis's profile (online now)


5057 posts in 2529 days

#10 posted 07-21-2016 01:10 PM

When you build “rustic”, that is what you get. Using plain sawn construction lumber, that is not fully dry will cup every time. To avoid this you need first get your lumber fully dry. Then rip out the centers, then glue the boards back together without the pith/ juvenile wood. That will give rift and quarter sawn lumber that is a lot more stable.

-- Bondo Gaposis

View rwe2156's profile


3144 posts in 1659 days

#11 posted 07-21-2016 01:25 PM

The center of the tree does not hold a lot of moisture

I didn’t know this…...

Deep in the recesses come forth botany from 45 years ago

—cambium, xylem, all that stuff

Yeah, I think the outer layers transport the water, don’t they?


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

View Aj2's profile


1814 posts in 1976 days

#12 posted 07-21-2016 02:10 PM

The Op said he built the table 1 1/2 years ago.If it was a high Mc don’t you think he would have been noticed the table cupping sooner.
Just putting it out there since we’ll never know.
What I see is a Diy table cobbled together with store bought construction lumber.I wouldn’t even call it rustic.Its more a picnic table.Nothing wrong with having a picnic style table for he house.Esp if it pleases the wife.
If the op would have followed the method used to make your common picnic style table things would have been different.
I suspect the under side of the table is screwed together in some dramatic fashion.New woodworker often go against mother nature thinking they will win.
It’s a good learning lesson for weekend woodwork.

Here’s a pic of a white pine table I made last month.Easy money.This is what’s trending.
As other mentioned you have to work with the wood.

-- Aj

View justinwacker's profile


4 posts in 854 days

#13 posted 07-21-2016 03:55 PM

Hey all,

Thanks for chiming in with various suggestions.

To add detail to my build, I didn’t really know how to attach the top to the base so I winged that. I didn’t want an apron all the way around, as that wasn’t what the wife wanted. I used my all too convenient pocket hole jig again. I made 4, I guess we could them cleats. 2 on each end of the table, inside the base. 2 or 3 screws to hold this 2×4 cleat perpendicular to the bottom of the top, like a “T”. And then 2 screws parallel to the top, straight into the base.

I am sure that while these joints on their own would have allowed for some movement, the solid as a rock base probably prevented them from doing so.

This project was done with pretty much a miter saw, skil saw, and a drill. I didn’t want to try running the long, heavy boards across my little table saw to clean up the edges, or make smaller boards. At least not by myself, maybe with an assistant. I don’t have a jointed or planer.

It sounds like the 2 biggest mistakes are using the lumber straight away when you get it home. But who has the time to wait weeks for it to dry out? Would a specialty lumber yard, rather Big Box store, sell actual dry lumber? We have plenty of ‘hometown’ sized lumber yards within reasonable distance.

Second, my attachment of the top to the base.

If you were going for this ‘rough’ look how would have joined the top pieces together? Would have ripped them into smaller pieces first? And second, how would you have attached the top to this base? Please include pics or links for this. Would you build an apron regardless whether you client or wife wanted one?

I get a lot ‘well the picture doesn’t have that’ when I make suggestions about how to do something in what I feel will be a better way.

View Aj2's profile


1814 posts in 1976 days

#14 posted 07-21-2016 04:46 PM

Heres the fastener I use the most.

It’s called a,figure eight.
Don’t bother buying the cheap stamped steel ones the screws will pull thru.
And most woodworker joint and plane their lumber.For a table top I will sometimes do it twice,That’s why wood must be bought over sized.
When it lays flat for a week or two then it’s ready.

-- Aj

View pmayer's profile


1032 posts in 3243 days

#15 posted 07-22-2016 01:52 PM

You’ll want to let your lumber acclimate a bit regardless of whether you buy from a big box or a lumber yard. In general, when buying from a big box you need to wait a little longer because the wood actually needs to dry a bit more. When buying from a reputable lumber yard that sells kiln dried lumber you’ll want to let it acclimate to your shop conditions because even though the wood was likely fully dried at one point the relative humidity is likely different in your shop from what it was at the lumber yard.

Having said all that, I believe that this problem was caused entirely by constraining wood movement while the wood was exposed to higher relative humidity. If the problem was caused by the wood drying when the movement was constrained, I would have expected to see cracks, and the problem likely would have appeared sooner. But instead the slab heaved, suggesting that the wood was swelling from increasing moisture content, and had nowhere to go but up. Another serious problem that I see is that the wood is painted on the top and not the bottom. This causes the wood to absorb moisture unevenly, and can definitely cause the table top to cup severely even if the wood movement is accommodated appropriately. I’ve seen examples far worse than yours from finishing only the top of a table. In general, whatever you do the top, you should also do to the bottom. Plane, sand, seal, pain, poly, whatever. Same products, same process, same number of coats.

-- PaulMayer,

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