Cupped Table Top, What would you do?

[Victor Stearns]

Greetings Creekers,
We have be asked to refinish several table tops. The first two, no problem.
This table on the other hand has me questioning what we should do.
It has a split in one of the glue seams. No biggy, just cut it apart and reglue it right?
Well we removed the table top and it is cupped. The top is 16-inches wide and made up of 1-1/2 inch strips of oak.
As you can see in the picture, the cupping is too much to not address.
I am guessing that we have three options.
1. Cut and glue only the one section and leave the cupping alone
2. Disassemble the entire top, run through the joiner and re-glue
3. Make a new top
Your thoughts?
Victor

[Jason Roehl]

I'd take the finish off the top and bottom, then let it sit for a while in a conditioned area to see what it does. If it goes back to flat, then I'd refinish the top and bottom as equally as humanly possible (perhaps repair the glue check in there somewhere).

[Carroll Courtney]

Guessing it pulled away from the apon,strip the screws out,does it take alot of force to push it flat?If it was poorly attach to the apon them maybe all it needs is to be reattach if only alittle force is needed to flatten it out.I think that sometimes only the top side has a finish but I think that both sides needs to have a finish to help in staying flat.I seen this on one of those shows where they took a board and put the cup side down in the yard for afew hrs and then it flatten out some.Just a thought----Carroll

[J.R. Rutter]

I seen this on one of those shows where they took a board and put the cup side down in the yard for a few hrs and then it flatten out some.Just a thought----Carroll

Right - just make sure that you do this on a sunny day when the bottom side can get warm. (Never hurts to be too specific!) This dries the bottom and feeds some moisture into the top side.

[Mel Fulks]

The way I understand it the cup was caused by "compression ring set" from water applied to the top. The conservator way of flattening is to get moisture into the bottom. The cells near the surface then try to expand,but they are constrained by the greater number of dry cells.So they distort into ovals,when they dry and shrink they exert force balancing the force on the top. Counterintuitive ,but true.

[Mel Fulks]

Post script: I first read of the effect in an article by Bob Flexner and went to the trouble to test it by intentionally warping a board ,letting it dry then flattening . A newly planed board left on a flat surface may indeed roll up a bit from losing moisture from the top side,that's what makes the proposed fix for the table seem wrong. In short a warp can be caused by loss of moisture or be permanently distorted by absorbing moisture (forcing cell deformation) then losing moisture.

[John TenEyck]

Have you asked the customer for their input? That would greatly influence what options were open for me. Without any guidance from the customer, my first move would be to measure the MC on the top and bottom. If the readings are equal then the top is permanently warped and any fooling around with adding water on one side, putting it in the sun, etc. won't provide a permanent solution, and maybe not even a temporary one. In any case, if the MC's are the same, you're left with cutting it apart, jointing, planing, and regluing, or just building a new one. IMHO, unless the grain is spectacular, or you can't get that particular species of wood, you are better off making a new one.

John

[Mel Fulks]

I agree with John about having a talk with the customer, but the top can be greatly improved at extra cost. I never encourage anyone to replace a top. I know it is frustrating to get conflicting advice about which side needs to be treated.I suggest you find the Flexner article and the post where George Wilson described the same flattening method. It takes time but works. If they turn down that treatment the top could be removed ,blind kerfed and put back. Brutal but effective.

[Jim Matthews]

I'm late to the party on this one.

Was the customer complaining of a table as unusable?
It may be that this didn't cause any problems - the hollow in the middle.

It's not as if things will roll off a surface like this.

I'm wondering if a subtle coopering of the center would get the ends down closer to horizontal.
If you must scrape off the old glue, anyway - it could be done.

Only one piece would need attention - the sides could be planed square.

[Victor Stearns]

Creekers,
Thanks for the great responses.
I have not yet approached the client as I want a solid solution first.
We are working on wetting on side of the table to introduce the moisture that may help with this issue in the hope that if will become more towards flat that when we started.
They did not complain about the cupping. I think that when the top was screwed to the apron, it was more "flat" than when the top was released.
I am hoping that we see positive results tomorrow evening.
I also do not think that the client would be opposed to a new table top, but I would rather save what we have today.
Victor

[Myk Rian]

I'm going with #2, but only rip it into thirds, (2 rips) glue it up, and drum sand it flat.
That way you would lose the least amount of thickness, and width.

[Lee Schierer]

I would bet that there is little if any finish on the underside, which is typical of older furniture.

I would remove all traces of finish from the top, run a wet rag over it getting the surface quite wet and let it sit over night. In the morning you will find a bit of raised grain on the top surface, but the top will be much flatter. Rip the separated part free and joint the edges. Glue teh pieces back together and go through your planned finishing routine and be sure to put equal amounts of finish on all sides. Then secure the top to the apron so that seasonal moisture changes allow the top to expand and contract while holding it tight to the apron.

[Mel Fulks]

Has anyone here ever seen an old table top cupped in the other direction ? Microanalysis has proved that the tops curl up from repeated application of water. The research was done on,and to improve some very expensive and rare tables. As one who was wrong about the best fix for a long time and had to test the newer method to believe it ,I suggest reading the Flexner article and testing.The temporary curling of a new board from loss of moisture ,or short term exposure to moisture is entirely different from the permanent cell distortion (elongation) found in old table tops.

[Tom Hammond]

There's NO WAY I would apply water to this top, using a wet rag or otherwise. It'll just make the problem worse. Here's a technique that, if it's not too far gone, actually works:

Take the top off the legs. Turn it face down (hump up) on some sawhorses and set it in direct sunlight for about an hour or so. Then put it in a shady, humid place. The next day do the same. Keep doing this and measure the center off of flat. For tables that weren't completely stabilized in warped condition (due to long period in this condition), I've been successful in getting them flat or close and retabilizing them in flattened condition in a few days.

Try this experiment in your shop sometime (use something like poplar to minimize the expense for this exercise). Get some new finished lumber out of the center of a stack to make sure it's not dried out. Cut and glue boards into two 22x48 (or so) panels. Once you've unclamped them, scrape the glue and give a light sanding, verifying flat. Stand them vertical on end together (face-to-face)... and keep them touching, making sure they're not leaning against a wall or stacked with other panels. Give them about a week, and you know what you'll have? Unless those boards were completely, totally, absolutely stable, (or the humidity is so high it's practically raining in your shop) you're going to have two warped panels, their convex sides touching. It's because of the uneven moisture content caused by the fact one face was exposed and one was not. Turn the boards the other way and let them go again... bingo, flat again. It's like magic.

If leveling the moisture content does little or nothing, ripping the boards on their joins using a thin-kerf blade and rejointing may be your only option to maintaining the integrity of the top... but even then the individual boards may still be cupped. I hate stripping the finish unless I absolutely have to, though. Good luck.