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I will be using 10-ft x 2" x 6" treated lumber for a rail. Will treated wood used as a rail warp?

Let me explain the application:

I have a 10-ft 2"x6" piece of treated wood that will be attached at each end (with screws) to two 4"x 6" steel bases anchored to concrete.

I assume that length-wise it won't warp since it's anchored at each end. Width-wise, the 4"x6" steel base will have (4) holes on each corner holding the piece of wood. My thought is that there's no way it will warp since all the area (width-wise) is held down by a screw.

This is the idea. Will there be any very noticeable warping in this case? enter image description here

  • Having just built a fence with treated 2x6x8' rails I'd suggest both being selective with the wood you get and securing the boards while they're still wet. I tried letting mine slowly dry in a shaded, elevated area, flipping them at least daily to allow them to dry evenly, but I had much more warpage doing that than when I mounted them wet. Wood with more rings in it has tended to warp less on me as well. Treated wood can warp like nothing else. – Egg Mar 27 '18 at 18:58
  • for a small job consider composite deck lumber.. – agentp Mar 29 '18 at 0:49
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Treated lumber is more likely to warp due to its high moisture content, and the outcome depends on several factors:

  • How securely it's mounted - warpage can create strong forces, but they can be resisted in some cases.
  • How quickly it's allowed to dry - direct sunlight dries the exposed surfaces quickly, exacerbating warpage.
  • The grain of the board - those with cupped grain are more likely to experience cupped warpage.
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Exposed to elements wood of any kind could warp or twist or even cup. A 2x6 deck board should have a cup over the width to begin with, this is for drainage. If you install it upside down it will collect water and warp. Right side up and water should shed away. After many years, you could potentially see a twist. Install cupped side down, with a small amount of spacing under it, or cut some grooves to allow for water run off.

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