Cupped outdoor table top...looking for advice - Woodworking Talk - Woodworkers Forum
 
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post #1 of 8 Old 06-26-2017, 10:55 AM Thread Starter
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Cupped outdoor table top...looking for advice

I recently built a tabletop for a customer to fit onto an aluminum table base. The top measures 10ft long x 36" wide x 1" thick. It's made from sinker cypress and I used festool dominos (sipo mahogany for outdoor use) and Type III glue for joinery for a seamless top. I then did 6 coats of Epifanes marine spar varnish on all sides/faces. I secured it to the base through inside tabs on the base with screws running through it and into the underside of the table. I tightened the long center tab screws and loosely attached the other screws for anticipated expansion/contraction. This table sits in full sun, no shelter from rain or other elements in Florida. You can imagine how this is a high heat, high humidity environment. About 5 days after delivery (and lots of rain in those days) the top cupped pretty severely. I haven't seen it in person but the owner sent a picture.

Does anyone out there offer any advice for a fix? The customer and I both want to avoid a total rebuild. She wants it fixed, not replaced. Thanks in advance for advice.
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post #2 of 8 Old 06-26-2017, 06:42 PM Thread Starter
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Nobody?

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post #3 of 8 Old 06-26-2017, 07:20 PM
where's my table saw?
 
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Somebody....

If you did not coat the back/bottom side as well as the top with your finish, there is your problem. The top gets baked and soaked, but not the bottom.

I'm not sure if there is a cure, because the uppermost surface has shrunk and the lower portion has expanded to create the "cup". You could unscrew it and turn it over and then..... clamp it on the table with a spacer in the center to "reverse" the cup ..... bring it into a humidity controlled environment and see if will return to flat..... clamping with curved cauls may help... do not store it directly on a concrete surface, keep it elevated at least 24" above.

It's a bit of a crap shoot at this point. :frown2:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #4 of 8 Old 06-26-2017, 07:36 PM
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Are the separate boards radial grain or tangential grain? They look tangential in the pcs but can't really tell. If tangential and are the same side up can cause cupping.
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post #5 of 8 Old 06-26-2017, 08:10 PM
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Ok, you coated both sides like you are suppose to. A finish, even Epifanes isn't 100% waterproof. The heat from the sun will vaporize what moisture there is in the wood enough to escape through the finish and dry the top side of the table out. This leaves what moisture there is in the wood on the underside so you have a moisture imbalance just as though you didn't finish the underside on an interior table. About all you can do is fix the base of the table so it has enough elongated mounting holes you can put enough screws into the top to combat the warpage. Even if you make a new top it will do the same thing so you might as well fix this one before it gets any worse. Force the top flat with clamps and bolt the H out of it. Just be sure to leave the bolts loose enough the top can expand and contract width wise.
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post #6 of 8 Old 06-27-2017, 09:14 AM Thread Starter
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Quote:
Originally Posted by Kerrys View Post
Are the separate boards radial grain or tangential grain? They look tangential in the pcs but can't really tell. If tangential and are the same side up can cause cupping.
Most are tangential. I think two of them were radial but I separated them in sequence. With the tangential grain, I alternated bark side up, bark side down, etc to help with potential cupping.
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post #7 of 8 Old 06-27-2017, 09:16 AM Thread Starter
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Quote:
Originally Posted by Steve Neul View Post
Ok, you coated both sides like you are suppose to. A finish, even Epifanes isn't 100% waterproof. The heat from the sun will vaporize what moisture there is in the wood enough to escape through the finish and dry the top side of the table out. This leaves what moisture there is in the wood on the underside so you have a moisture imbalance just as though you didn't finish the underside on an interior table. About all you can do is fix the base of the table so it has enough elongated mounting holes you can put enough screws into the top to combat the warpage. Even if you make a new top it will do the same thing so you might as well fix this one before it gets any worse. Force the top flat with clamps and bolt the H out of it. Just be sure to leave the bolts loose enough the top can expand and contract width wise.
I'm leaning toward clamping and running a ton of screws from the underside through the slotted tabs of the table base. I realize I'll need to gradually clamp it though. If I horse it down too fast I bet it'd crack. I agree with you that a new top will do the same thing.

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post #8 of 8 Old 06-27-2017, 01:24 PM
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I don't think you will win this battle.




I would flip it over until it flattens. then rip it into 8-10" wide strips (finish edges) and attach them with cleats underneath. it will still warp but will be usable.
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