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I've built many retaining walls and garden beds with class 2 hardwood sleepers (2.4m x 200mm x 50mm). A few weeks after installing them in a vertical position with no gap between sleepers, a significant (over 10mm) gap develops between the sleepers.

enter image description here

As shown in the photo, the sleepers are screwed into the steel posts, so it doesn't seem likely that they are moving away from each other.

I assume that they are shrinking? If so, why? These aren't new sleepers - sometimes they've been lying around for months before use.

lithic
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1 Answers1

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What you are showing is bare wood apparently without any treatment or coating. In that case the wood will shrink and swell due to humidity and, since this appears to be outside, rain, snow, etc.

Wood changes dimensionally the most at right angles to the grain. In your case the grain is going horizontally and so the dimensional changes will happen most in the vertical direction. That, of course, is exactly what you are seeing.

If you don't want this to happen, there are two options that I can think of:

  1. Treat the wood (usually this means primer, paint) with a product that will seal it against humidity and moisture. This will likely need to be redone periodically.
  2. Replace the wood with a product that is not subject to moisture.

Otherwise, what you have is entirely normal. You could just live with it as it is.

jwh20
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