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I am building a kitchen island. On top of the carcass is going to be a piece of plywood, and on top of that a laminated solid wood plank top of 3/4" thick planks. The plywood is to provide enough support for the overhang so I don't have to install corbels or legs.

I painted the plywood underside before attaching it. After I painted it, it cupped. I screwed the plywood down and now one corner kicks upwards a little.

Is there some way that I can make this plywood lay out flat? Or, should I leave the plywood with the lift and somehow level out the counter top?

Here is the plywood unattached: enter image description here

If I screw the plywood down into the frame, the front corner lifts up like here: enter image description here

Here is the top that I built that will go on top of the plywood. It is built with a laminated lip: enter image description here

  • 1
    what type of plywood is that? A/C exterior grade? I would think you'd need multiple layers of a better grade of plywood. – zipzit May 3 '16 at 3:39
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    Very related Answer here. – Graphus May 3 '16 at 9:06
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    Have you tried setting your top on the ply and clamping? (No glue, no screws.) Intuition tells me it'll flatten out and you'll be fine to put it all together with lots of glue/screws and clamping for the final product. – Aloysius Defenestrate May 3 '16 at 13:59
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    Is it painted on top as well or no? If this wood is to be hidden you could paint both sides and possibly flip it over so the warp is facing down. – Matt May 3 '16 at 16:09
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    "After I painted it, it coupled" - I presume that means "curved", "warped", "cupped" or something similar (darn auto-correct). Are you sure it was actually flat before you painted it? If so, your paint may have gone on too heavily, wetting the plys enough to allow them to warp. How are you planning on attaching your plank top to the ply substrate? You asked a question about that, and your accepted answer suggested you shouldn't try it due to the high likelihood of the final product warping. – FreeMan May 3 '16 at 17:52
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I don't know how important this project is, or what your budget is, but in the long run, doing this right will save you money. If it was my call to make, I would do the following:

  1. Scrap the plywood for another purpose.
  2. Cut 3/4" MDF to size. MDF is more dimensionally stable so long as you don't soak it directly with water. See step 3 for this.
  3. Seal and paint the MDF. See this article: http://www.finewoodworking.com/how-to/article/tips-for-painting-mdf.aspx
  4. Attach it and proceed with the rest of the project.

Best of luck! Don't waste too much time agonizing over the plywood, your time is of value, too! PS - I'm not seeing why you need to paint, won't this part be concealed anyway? I think some sealing as per the article might suffice.

  • I think this is my best options, thanks. If I decided to use corbels in order to pull the plywood down flat, would that be a bad idea? I do need to paint the inside, because the island has a built in dog crate, so the bottom of the plywood will be the "ceiling" in the crate area. – ScottK May 4 '16 at 16:00
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    I'd agree with #1 wholeheartedly! @ScottK - either ask a new question, or put the corbels question into your original post - I think it's related enough to be part of this question. It will get lost down here in the comments, though. – FreeMan May 4 '16 at 16:40

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