# Why did it warp and how to avoid it?



## justinwacker (Jul 20, 2016)

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.


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## DirtyMike (Dec 6, 2015)

was the lumber kiln dried? pocket screws huh?


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## Unknowncraftsman (Jun 23, 2013)

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

Aj


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## ChefHDAN (Aug 7, 2010)

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.


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## FLBert (May 19, 2016)

Justin,

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.


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## rwe2156 (May 7, 2014)

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.


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## pintodeluxe (Sep 12, 2010)

Using quartersawn lumber will help with future projects.


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## TheFridge (May 1, 2014)

Ana White?


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## BLarge (Aug 29, 2011)

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!


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## dbray45 (Oct 19, 2010)

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.


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## bondogaposis (Dec 18, 2011)

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.


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## rwe2156 (May 7, 2014)

> 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?

;-)


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## Unknowncraftsman (Jun 23, 2013)

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.


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## justinwacker (Jul 20, 2016)

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.


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## Unknowncraftsman (Jun 23, 2013)

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.


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## pmayer (Jan 3, 2010)

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.


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## Ger21 (Oct 29, 2009)

> 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.


The biggest issue is your choice of materials.

Construction lumber is "kiln dried" to about 18%-20% moisture content. So they will still continue to dry for quite a while after you purchase it.
It's also often cut from very small trees, often from the center of the tree.
Both of these issues means that it will warp, no matter what you do.

If you want to build furniture with construction grade pine, then buy it a few months in advance and stack and sticker it to allow it's moisture content to equalize.
And then I'd still recommend a planer and jointer to get them flat.

Hardwoods are kiln dried to about 6%. Depending on where you live, hardwoods can actually get more wet after you purchase them, as their moisture content equalizes with their environment.
Many smaller hardwood lumber dealers offer jointing and planing services for a small fee.

If you want a "rustic" look, you can get #1 or #2 common red oak very cheap, and it will be much more stable than what you're working with.


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## Scottlj (Sep 11, 2013)

Lot's of basics already covered. I'll add a few ideally not overly repeating.


Wide boards: It looks like there's cupping just within some single boards alone. This is less of an issue with less wide boards; though of course can still happen across a span.


While an apron is often used, it's of course not necessary. But when you attach to the pedestals, you need some way to float the top at least a little to allow for the expansion / contraction. While pocket hole joinery is great and I certainly use it a lot as well, there's times when it's a bit sub-optimal. Here's an option I might have applied here, and you actually still could…

(This won't make sense until reading through the whole thing, but the idea here is to use threaded inserts in the top, and some custom sized threaded rod to do the attachment such that the top will float. I'd love to make a picture for you, but I won't be back to my pc with sketchup for a while so hopefully this will make sense.)

- On the bottom of a main trestle, you're going to attach this directly to the top, but as follows…

- First I'm assuming you were doing this from scratch or disconnected the top of this completed table top from the pedestals.

- Go halfway / center to where one of the top boards would lay on the pedestal and mark that center.

- Use something like a 1" Forster bit to put a 1" intended circle about 1/2" deep. Drill maybe two more of these overlapping on either side of the center, (for four total), such that you end up with maybe 3/4" worth of oval mortise. (Chip out the bits that remain with a good chisel.)


Drill something like a decent 1/4" sized hole up through the center of this mortise you've created.


Use a circular or oval file to expand the hole along the length of the mortise. This may be problematic for that much thickness of wood though. Maybe easiest to make a jig for a router or use a drill press or a hand drill with a block or something to expand the hole.


What you should end up with is a 1" wide mortise 1/2" deep, with a horizontal hole that's 1/4" to take on a screw.


Only you're not going to use a regular screw. First you do all these holes, (one one each side of each pedestal). Position the table top and use a pencil through the center of each mortise / screw hole to mark it.


Now, at those marking points, use threaded inserters for 1/4" rod, (you can get these at Rockler, Woodcraft, etc.), and install them.


Get some 1/4" x 20 thread steel rod. This stuff is really inexpensive. We're talking just a couple bucks for three feet of it at your home center.


Get some "Cap Nuts for Connector Bolts" you can also get at a variety of woodworking stores.


Measure how much rod you need to cut to go through the pedestal and into the threaded insert such that there's just the right about coming out of the mortise so the Connector Bolt can go on to hold it. (There's a sleeve around the connector bolt, so it's possible a small portion of the 1/4" hole needs to be a tad wider.)


Screw these in, but don't crank them down with all your might. Just make them plenty sung.

THE END RESULT SHOULD BE… A top that is securely attached to the pedestal bases, but where if the top expends or contracts width-wise, all that will happen is the connector bolts will move a little bit in the slots. But there won't be crazy stress on the top.

This might not help individually very wide boards from warping, but it should keep the whole thing from just failing / cracking.

Scott


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## a1Jim (Aug 9, 2008)

Hi Justin welcome to LJs
Lot's of people have mentioned it's not a good idea to use construction lumber because it's too wet and through the process of drying it changes shape and even more so when the wrong joinery will not allow it to move. Here's a link I give my woodworking students so they can understand wood movement and joinery that help compensate for this movement,this can help in future builds.

http://toddpartridgedesign.com/sr_pages/documents/UnderstandingWoodMovement.pdf


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## wormil (Nov 19, 2011)

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


Sorry, didn't read all the replies but the ones I did read were full of good advice. I didn't see it mentioned but alternating the grain is a myth in the sense that it is supposed to prevent your top from cupping but as you can see, it doesn't. In fact, your table is a textbook example of why alternating the grain is a bad idea because the worse case scenario is your caterpillar top! And it's the most difficult type of cupping to fix. Another mistake is finishing the top but not the bottom, you want to finish both sides equally and alternate as you go-top, bottom, top, bottom. Your method of joining the top to the battens was fine but you need to wallow out the screw holes so that top can move around. Construction pine is relatively wet and will do a lot of shrinking for a year or so. There is a small chance that if you relieve those screw holes and then finish the bottom, the table might flatten out a bit but it will take time.


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## BB1 (Jan 29, 2016)

Thanks for this link…saving it for my own reference!


> Hi Justin welcome to LJs
> Lot s of people have mentioned it s not a good idea to use construction lumber because it s too wet and through the process of drying it changes shape and even more so when the wrong joinery will not allow it to move. Here s a link I give my woodworking students so they can understand wood movement and joinery that help compensate for this movement,this can help in future builds.
> 
> http://toddpartridgedesign.com/sr_pages/documents/UnderstandingWoodMovement.pdf
> ...


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