Cupped tabletop - could it be related to water-based dye?

[Alex Vessey]

Hi everyone,

I'm working on a 60x32 inch maple table top and I've run into a problem, notably that the wood has cupped. I bought it from a big box store so I figured it was dried to the point of being ready to use (though I don't have a moisture reader). I did my glue up and was left with a pretty flat top that was level across both diagonals. I then let it sit for a week with pretty adequate air flow on each side before coming back and working on the bottom as follows:

-Wet the wood to raise the grain. After an hour I sanded gently with 320 grit to knock off the fibers.
-Flood with General Finishes dye stain and wipe off.

I got a nice color, but here's where I wonder if I made mistake. I wasn't entirely sure how long to let it dry so after about an hour I applied my first seal coat of shellac. After another hour I applied the second coat of shellac and then, after another 2-3 hours I applied a coat of minwax polycrylic. I let this sit overnight and then applied the final coat of polycrylic. It was at this point that I noticed that the table has cupped such that what will be the top is now convex. I don't think it's severe but it's definitely noticeable (I can measure when I get home but I'd say maybe 1/4 an inch?).

I'm wondering if this could be caused by sealing the water-based stain too soon. I'm reading around about cupping solutions (blind kerfing etc.) but I'm beginning to wonder if I should strip off my finish back down to bare wood and let it dry for a week to see if this fixes itself. Or, if I go to do the top tonight and repeat the grain raising/stain, is there a chance this would even it out?

If anyone has run into this I'd love to get your feedback. It's my first project and was going great up until this point so I'm hoping I can salvage it! Thanks!

[Prashun Patel]

It's possible wetting it has caused it to cup. This has happened to me too. You can try flipping it and leaving it be for a little while first. My maple top flattened on its own this way.
You should also check if the edges can be pulled into compliance. Your apron may be able to right this if the cup isn't so bad.

[Alex Vessey]

It's possible wetting it has caused it to cup. This has happened to me too. You can try flipping it and leaving it be for a little while first. My maple top flattened on its own this way.
You should also check if the edges can be pulled into compliance. Your apron may be able to right this if the cup isn't so bad.

Thanks Prashun! I'll check how pliable it is tonight; my first thought was that anchoring it to the apron may indeed draw it back towards flat but I figured I should explore other options so I don't go down that path only to find out it doesn't help and now I have a table I can't set a pen on, hahah.

Do you think I should wet/dye the open side and let it sit for a bit or just leave it bare and see what happens? I'm going to dye it at some point anyway but I can hold off if that might help.

I should also note that this is in MN where the temperature and humidity can swing wildly from one day to the next during the summer.

[Andrew Pitonyak]

It sounds like you added dye and did not notice cupping. You then added shellac and noticed cupping? Is this correct?

In general, what you do to one side you should do to the other. I have never bothered to do this with dye or stain, but certainly with most of the other finishes.

[Alex Vessey]

It sounds like you added dye and did not notice cupping. You then added shellac and noticed cupping? Is this correct?

In general, what you do to one side you should do to the other. I have never bothered to do this with dye or stain, but certainly with most of the other finishes.

Honestly, I'm not sure if the curve was there pre-dye or not, but it was flat exactly a week prior. I figured it was more likely that the introduction of water brought it about vs. what I hoped was stable wood cupping on its own, but I may be wrong.

I also figured I'd be OK to do one side and finish the other up the next day, but I may certainly have been wrong there too! Live and learn, I guess :)

If it was, in fact, humidity that caused this then should I just let it sit for a while and see if it straights out? Or should I wet the other side and let it sit? Or remove the poly and shellac and let it sit? I'm out of my depth here :)

[John TenEyck]

I would finish the other side as soon as possible then let it sit. If it truly was flat before you started finishing it I bet it will straighten out on it's own, but it might take a week or two.

As mentioned, what you do to one side you should do to the other - right away. It the top had been anchored down to the aprons before you finished it then that's a different story. Many table tops were, and still are, finished only on the top. They don't warp because they are fastened to the aprons first.

Trusting lumber to be dry is an invitation to problems. A moisture meter is not very expensive and one of the best investments a woodworker can make.

John

[Alex Vessey]

I would finish the other side as soon as possible then let it sit. If it truly was flat before you started finishing it I bet it will straighten out on it's own, but it might take a week or two.

As mentioned, what you do to one side you should do to the other - right away. It the top had been anchored down to the aprons before you finished it then that's a different story. Many table tops were, and still are, finished only on the top. They don't warp because they are fastened to the aprons first.

Trusting lumber to be dry is an invitation to problems. A moisture meter is not very expensive and one of the best investments a woodworker can make.

John

Ok, I'll give that a try, thanks!

The only question that raises is that if I finish the top won't there be no way for the moisture to transfer(and thus no way for it to revert to its original shape?). This is why I'm curious if I should remove the finish/sealer from the bottom then dye the top so that both sides have experienced the water from the dye but the surface is open for any moisture transfer that needs to happen.

[Steve Schoene]

General Finishes doesn't sell dye, they sell a dye stain. It uses dye for the colorant, but it is mixed with a waterborne binder that has acted as a sealer, unlike what a straight dye would have done. You can't remove the sealer without removing the dye. With this product I would have stained the bottom, and then immediately flipped it over and applied the same stain to the top. Yes, there will be a few small marks where the underside was supported, but they are on the bottom and don't matter. Then you can apply top coats after the stain on both sides has well dried. That's of course just hind sight at this point.

At this point I would anchor the top to your rails. I'd bet it will pull down flat pretty easily. Then you can apply the stain to the top, and go on as if nothing had happened. You will only have to take more drastic steps if the top won't pull down flat to the rails.

And I'll also echo others that wood purchased from the big box stores can't be counted on to be dry, or for that matter free from drying stresses. I use it only in extremis.

[John TenEyck]

Finishes do not stop the transport of moisture vapor back and forth between the wood and atmosphere. Finishes slow down moisture vapor transport, but they don't prevent it. Verification can be seen every Summer when doors stick and every Winter when they don't. And that's why I offered the recommendation I did.

John

[Alex Vessey]

Finishes do not stop the transport of moisture vapor back and forth between the wood and atmosphere. Finishes slow down moisture vapor transport, but they don't prevent it. Verification can be seen every Summer when doors stick and every Winter when they don't. And that's why I offered the recommendation I did.

John

Got it! I checked today and it was somewhere between 1/8 and 1/4 an inch bowed in the middle (concave on the top side). It was pretty easy to push down so I'm hoping that attaching it to the apron takes care of the issue but we'll see. I wasn't able to get it finished up today as I realized I had some emergency sanding to do but it'll go on tomorrow so hopefully there's no more movement over night.

And yes, definitely avoiding the big box stores in the future and going straight to a lumberyard, though that tiger maple I found for 5 bucks a bf was a pretty sweet find!

Thanks for weighing in everyone, your advice is incredibly helpful to new folk like myself!

[John TenEyck]

Good luck.

Just a comment about wood in general. Don't expect a lumber yard to offer wood any drier than what you get at the BORG. The only wood that's guaranteed to be a certain MC is the stuff bought by high volume users. Little guys like us get what we get. That leaves us with only a couple of options. Buy a moisture meter to test and approve/reject accordingly, or buy whatever we want and then store it until the wood has come to equilibrium with our shop. I do both because it's really rare to buy wood that's has the same EMC as my shop.

John

[Kent A Bathurst]

I let this sit overnight................ If anyone has run into this I'd love to get your feedback.


Yes, I have. Developed an entire new subset of cuss words for this event.

Key question:

When you were doing the finishing - especially the "sit overnight" bit - was the table top on a flat surface, or did you have it elevated on some stickers/painter's points/etc.?

I have always been very, very impressed at how much flat surfaces will cup if left laying on top of a flat surface, with nothing to elevate it. Even overnight.

Me - I lay donw 2 x 4 scrap, with clean, dry, soft cotton rags for padding laid on top. The workpiece goes there. Finish edges and top surface. Come back tomorrow, flip it, and do a lick-and-promise finishing job on the bottom side ["pretty" ain't in it]. Rinse. Repeat.

[Alex Vessey]

Yes, I have. Developed an entire new subset of cuss words for this event.

Key question:

When you were doing the finishing - especially the "sit overnight" bit - was the table top on a flat surface, or did you have it elevated on some stickers/painter's points/etc.?

I have always been very, very impressed at how much flat surfaces will cup if left laying on top of a flat surface, with nothing to elevate it. Even overnight.

Me - I lay donw 2 x 4 scrap, with clean, dry, soft cotton rags for padding laid on top. The workpiece goes there. Finish edges and top surface. Come back tomorrow, flip it, and do a lick-and-promise finishing job on the bottom side ["pretty" ain't in it]. Rinse. Repeat.


Funny as this sounds it was sitting on two rubbber garbage cans. Not ideal for airflow to the bottom, but not stifling either. Your 2x4 idea is the way to go for next time for sure! I'm guessing it was wet wood and/or the wacky humidity changes we get here during the summer.

I had to sand out some nasty grooves tonight so I clamped it down to the table for a flat working surface and it flattened out super easy. Hopefully installing it to the apron will have the same effect.

[Kent A Bathurst]

......... it flattened out super easy. Hopefully installing it to the apron will have the same effect.

Should be no problem.

[ron david]

Hi everyone,

I'm working on a 60x32 inch maple table top and I've run into a problem, notably that the wood has cupped. I bought it from a big box store so I figured it was dried to the point of being ready to use (though I don't have a moisture reader). I did my glue up and was left with a pretty flat top that was level across both diagonals. I then let it sit for a week with pretty adequate air flow on each side before coming back and working on the bottom as follows:

-Wet the wood to raise the grain. After an hour I sanded gently with 320 grit to knock off the fibers.
-Flood with General Finishes dye stain and wipe off.

I got a nice color, but here's where I wonder if I made mistake. I wasn't entirely sure how long to let it dry so after about an hour I applied my first seal coat of shellac. After another hour I applied the second coat of shellac and then, after another 2-3 hours I applied a coat of minwax polycrylic. I let this sit overnight and then applied the final coat of polycrylic. It was at this point that I noticed that the table has cupped such that what will be the top is now convex. I don't think it's severe but it's definitely noticeable (I can measure when I get home but I'd say maybe 1/4 an inch?).

I'm wondering if this could be caused by sealing the water-based stain too soon. I'm reading around about cupping solutions (blind kerfing etc.) but I'm beginning to wonder if I should strip off my finish back down to bare wood and let it dry for a week to see if this fixes itself. Or, if I go to do the top tonight and repeat the grain raising/stain, is there a chance this would even it out?

If anyone has run into this I'd love to get your feedback. It's my first project and was going great up until this point so I'm hoping I can salvage it! Thanks!

some times we do things without thinking and perhaps in your case you didn't just know. this is where experience helps and the knowledge is there to deal with it. in the following link the project which I had just completed to the finishing stage such an instance happened. I went to seal the bottom 1st and have that out of the way. I sealed it with shellac and looked at it about 15 minutes later and the whole thing had cupped. I said a few words , turned it over and picked up a gallon of methyl hydrades and wet the whole top down. 15 minutes later it was level again. can't remember though how long it took for my heart to get back to normal
http://www.sawmillcreek.org/showthread.php?197975-Seeking-butcher-block-information
ron