Why are my boards warping?

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I have cedar picket fence boards purchased from Menards that were planed and nailed together to make a DIY sign to paint on. They are warping now that they are put together. I made another and tried painting to seal it immediately and same thing. Wood was not wet and set in the house several days after I'd bought it, then in the garage for a month. What am I doing wrong? Is it just because it's cedar? Or the wood is too thin? or?

  4 answers
  • Seth Seth on Jan 02, 2019

    K-n-T,

    Cedar generally is a very stable wood as is redwood so I don't think it's the species of wood that is the issue, unless Menards is buying bottom of the barrel boards to begin with from parts of the tree that have imperfections. When you say "warped" what exactly is happening to the boards and how are you fastening them? Are they bowed, checked, crooked, cupped, etc.? How much did you plane them down and what is now their thickness? A picture would be helpful if possible.

    • Kelly-n-Tony Kelly-n-Tony on Jan 02, 2019

      both sides planed lightly. 1/2 inch thickness. they were attached with glue and nailed as well. it is bowing into a U shape but not extreme. still enough that it isn't going to lie flat on a wall.

  • Kelli L. Milligan Kelli L. Milligan on Jan 02, 2019

    Probably too thin. Are you paining both sides? Only one side could cause it to warp. Also wood can feel dry and not actually be. You would be safer buying cedar planks that have been kiln dried.

    • See 3 previous
    • Kelli L. Milligan Kelli L. Milligan on Jan 03, 2019

      What I was trying to say is they should be primed and painted on both sides and edges. Can you try oil based primer? Wouldn't put as much moisture into wood.

  • Sometimes if wood is attached together too tightly, it warps. It needs room to expand.

    • Kelly-n-Tony Kelly-n-Tony on Jan 03, 2019

      I wonder if this is it. We've been gluing between the pieces in addition to 2 or 3 pieces of wood on back nailed to it

  • Seth Seth on Jan 03, 2019

    It's weird that the planks are cupping and that it happened twice. Even at only 1/2 an inch thick, they should not automatically do that. Glueing along the grain between the boards would not cause that to happen. That is how you would glue up any multi-piece panel. Is each board cupping? Typically you would alter the end grain, one board up, next board down. Don't have them go all the same way. You could add biscuits or dowels between the boards to help strengthen and stabilize them, but you really shouldn't have to. Cupping happens when boards dry unevenly. How many boards are you gluing together? The wider the board, the more likely it will cup. Glue only two to start and add one at a time until you get the dimension you want. You could also rip the boards to a narrower width. While it's more work to glue up, they will be less likely to cup. Make sure the boards are flat when the glue is drying. You can actually use too much pressure with your clamps. I would agree with others that your boards are not as dry as you think they are. Go to an independent lumber yard and get a better quality kiln dried board. I think you will have better results. The pickets from Menards are probably among the lowest quality boards.

    • Kelly-n-Tony Kelly-n-Tony on Jan 04, 2019

      I just looked closely at the one we just finished a week ago and the 3 boards that are glued and nailed to the back are the culprits- they are bowing the whole thing.