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Jointed boards cupped

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Forum topic by v0mich01 posted 08-08-2018 12:16 AM 847 views 0 times favorited 12 replies Add to Favorites Watch
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v0mich01

1 post in 488 days


08-08-2018 12:16 AM

Topic tags/keywords: jointer cupping vanity spline dado cupped board

I’ve been working on a bathroom vanity counter top with my dad. We jointed the board(2×8) by running through the jointer, then cutting dados along with width of the boards, and gluing with a spline. All was well with that. Yesterday I was staining the counter before applying my sealer, and left it out in the sun to dry for four hours. In that four hours, they cupped(rookie mistake, now I know not to let it get too hot) Is there anything I can do to uncup?

This side is cupped worse than the other

Lesser but still cupped

I haven’t applied any sealer yet(I’m planning on using spar varnish)

Sorry if this is in the wrong forum, I figured since it is a joined board/panel this would be a place to start. Please redirect me if there is a better place.

Thanks!


12 replies so far

View BurlyBob's profile

BurlyBob

6765 posts in 2826 days


#1 posted 08-08-2018 01:29 AM

I had the same damn thing happen to me. Totally screwed up my plans for a project. I ended up using Oak plywood for an entertainment cabinet. I wasted almost $200 on that hardwood. I can totally feel your pain.

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Rich

5001 posts in 1150 days


#2 posted 08-08-2018 01:48 AM

You can try wrapping it tight in plastic and setting it cupped side down on two supports, place some weight in the center and leave it a couple of weeks minimum. Check it every day or two without unwrapping it to see if you’re making progress and to make sure you don’t wind up cupping it the other way.

If you can get it close to flat, then you’ll have a shot at pulling it flat when you mount it to the vanity. There should be room for a couple of battens underneath as well which will help. Of course all of the warnings about allowing for movement apply.

View bondogaposis's profile

bondogaposis

5570 posts in 2912 days


#3 posted 08-08-2018 02:30 AM

Just flip it over until the moisture content equalizes.

-- Bondo Gaposis

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clin

1072 posts in 1557 days


#4 posted 08-08-2018 10:59 AM

The problem isn’t that the sun heated the top, it’s that it dried it out causing the top to shrink. It may just flatten out on its own if you leave it alone.

What wood did you use? You mention 2×8 which makes me suspicious that you used construction lumber for this. Construction lumber isn’t dried out nearly as much as furniture grade wood. If this is the case, and the wood isn’t dry to start, the whole thing may turn into a potatoes chip once it does fully dry.

Pretty much any wood will cup and warp a bit if it’s moisture content changes a lot. This is especially true for flat sawn wood. So even if you build it flat, if after installation it dries out a lot more, it will likely cup and twist some. Possibly even split. Splitting may happen if in an attempt to keep it flat you screw it down tightly to the cabinet.

The internal forces caused by moisture changes in wood are huge. Swelling wood with water has been used to split rock. So if it wants to cup our twist, it will, or if held, it will split.

Regardless of all of that. Be sure to apply your sealer to both the top and bottom surface. This will not completely prevent moisture changes, but the sealer will slow the changes. By finishing the top and bottom the same, they will tend to change at a similar rate. You’ve already seen what happens when one side dries much faster than the other.

-- Clin

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ChefHDAN

1489 posts in 3410 days


#5 posted 08-08-2018 11:04 AM



What wood did you use? You mention 2×8 which makes me suspicious that you used construction lumber for this. Construction lumber isn t dried out nearly as much as furniture grade wood. If this is the case, and the wood isn t dry to start, the whole thing may turn into a potatoes chip once it does fully dry.
- clin

Same thought here,

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

View gwilki's profile

gwilki

329 posts in 2034 days


#6 posted 08-08-2018 02:10 PM

I would rip it again, but into 4 pieces instead of two. Joint and plain the narrower boards, then glue them again with alternating ring directions.

-- Grant Wilkinson, Ottawa ON

View Robert's profile

Robert

3569 posts in 2041 days


#7 posted 08-08-2018 02:16 PM

I hate to be the bearer of bad news and even worse, to disagree with Bondo (LOL), but IME once a board is cupped like this, it is unlikely to return on its own.

You have nothing to lose trying a couple things. One is to try to re- balance the moisture by either wetting the dry side, or drying the wet side, or both. IME wetting does not work. Therefore, put the convex side up in the sun maybe 1 hour at a time and leave overnight. Repeat if there is a response.

Another less harsh way is to put some battens across the panel with mild clamping pressure. Place the convex side up with fan blowing across it. (This is my preferred way because its more gradually allows the stresses to even out as the board dries).

Third, you can place the board on stickers convex side up with a little weight on top in a climate controlled area for a while.

Since this is a top, keep in mind it doesn’t have to be perfect, just close, any slight cup can be pulled out with installation to the cabinets. Be sure to allow for wood movement when installing. Do this by screwing rearmost and allowing expansion toward the front.

Worst case scenario, you may have to rip it apart, let the boards acclimate, and re-glue.

Good luck. Let us know what happens!!

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

View Rich's profile

Rich

5001 posts in 1150 days


#8 posted 08-08-2018 02:33 PM


I would rip it again, but into 4 pieces instead of two. Joint and plain the narrower boards, then glue them again with alternating ring directions.

- gwilki

You can see in the second photo that the rings are, indeed, alternating. The fact that they shouldn’t be is another matter.

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Rich

5001 posts in 1150 days


#9 posted 08-08-2018 02:35 PM

What wood did you use? You mention 2×8 which makes me suspicious that you used construction lumber for this. Construction lumber isn t dried out nearly as much as furniture grade wood. If this is the case, and the wood isn t dry to start, the whole thing may turn into a potatoes chip once it does fully dry.
- clin

Same thought here,

- ChefHDAN

I didn’t catch that at first, but you’re right. It looks like 2X lumber. Not only will it be unstable, but its surface will dent easily.

View Woodknack's profile

Woodknack

12945 posts in 2941 days


#10 posted 08-08-2018 04:53 PM


I would rip it again, but into 4 pieces instead of two. Joint and plain the narrower boards, then glue them again with alternating ring directions.
- gwilki

Alternating growth rings is a very old myth that just won’t die. If you don’t believe me, look at the op’s pictures again, they are alternated. When people talk about ripping into strips and flipping rings, I believe they have conflated the alternating growth rings myth and a technique sometimes called “rip and flip”. Rip and flip is a technique for stabilizing crappy wood where it’s ripped into narrow boards, turned 90°, and glued into a quartersawn panel. Rip and flip in my limited experience does not guarantee a flat panel but will give you a reasonably flat panel even from twisted wood.

-- Rick M, http://thewoodknack.blogspot.com/

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Woodknack

12945 posts in 2941 days


#11 posted 08-08-2018 05:00 PM


Is there anything I can do to uncup?
- v0mich01

You could try Bondo’s suggestion although I wouldn’t hold out much hope. Some people have success leaving it on the grass, convex side up. The bottom draws some moisture from the grass and the top dries in the sun which sometimes takes cup out, or makes it better. Construction lumber is only dried to around 14% moisture, something like that; while hardwoods are dried to 7-8% moisture. So this wood will continue losing moisture for some time to come and will be prone to undesired wood movement.

-- Rick M, http://thewoodknack.blogspot.com/

View GrantA's profile

GrantA

1972 posts in 1968 days


#12 posted 08-15-2018 04:51 PM

I didn’t see it mentioned but so you know, you should perform the same operations on top and bottom. After jointing a face then run it through the planer, to ideally remove the same amount of material from the other face.
With construction lumber the issues are compounded.
Also, not picking just so you know what its called – if you used a spline down the edges you didn’t cut a dado, it’s a groove.

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