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I've tried twice to resaw wood and both times experienced bad cupping.

To be clear, the cupping happens immediately. This is NOT a case of moisture causing the wood to cup overnight. I've read up on how to prevent that.

I've also tried the trick of spraying one side in hopes the wood will straighten back a bit but with no success.

My question is twofold. First is, is it likely that this is a result of internal stress being released... meaning that it's unavoidable and my only option is joint and plane. Or is it possible that my technique might be to blame? In the more recent case I tried to resaw a 2x4 on a table saw. I cut 49% of the way on both sides then snapped it off and hand planed the tiny middle section off. In another case I had a wider board that was too big to saw in half with power tools so I used a hand saw to do it manually.

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To be clear, the cupping happens immediately.

If it happens immediately the cause is not moisture loss as you say (although that will continue to cause issues as the formerly wetter interior surfaces dry out) it is tensions in the wood.

Some of this might be innate tension in the wood itself from how the tree grew, i.e. reaction wood. But with 2x material — especially in the smaller dimensions, with 2x4s possibly being the worst examples everywhere — it's very likely to be primarily due to case hardening.

2x4s, as bottom-tier construction wood, are well known for not being dried enough and hand in hand with this is that they are frequently or mostly dried too fast in the kiln, a sure recipe for case hardening. The two together are why 2x4s in particular are notorious for how often and how badly they can warp.

Safety note
For reference for any future readers unfamiliar with this issue, these are reasons for the absolute necessity of having a riving knife or splitter on a table saw. Assuming you do want to run it as safely as possible over the long term......

When working with solid wood of any kind it's not a question of whether you'll encounter reaction wood or case hardening, it's when.

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  • Please define "reaction wood", especially since you've got it in bold. That's a term I've never heard of. Maybe one of those fun "2 peoples separated by a common language" things...
    – FreeMan
    Commented Feb 12 at 17:12
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    @FreeMan I found this: botanicalgarden.berkeley.edu/glad-you-asked/reaction-wood
    – BVernon
    Commented Feb 12 at 19:08
  • Very interesting! I've seen that happen, but didn't know there was a specific name for it. Of course there is, it just hadn't occurred to me to ask...
    – FreeMan
    Commented Feb 12 at 19:12
  • @Graphus Between my 4 kids and needy wife, it's just a lot easier to get to Lowe's than a lumber yard. Plus I prefer to screw up new techniques I'm learning on cheap wood. That said, I'd still like to make the best of it. It sounds like I'd generally be better off buying 2x8s (at a minimum) and ripping in half before resawing to a 1-ishx size. Aside from that, I read a couple articles on case hardening and it sounds like it can be reversed... but it was unclear to me whether there are practical steps a hobbyist can follow to do this or whether it's not worth the effort.
    – BVernon
    Commented Feb 12 at 19:51
  • "It sounds like I'd generally be better off buying 2x8s (at a minimum)..." Yes actually has been recommended here a couple of times. It can be a very sound proposition IF one has the relevant tooling to make it practical. For anything other than a small project the one key thing is arguably a thickness planer, although ideally planer + bandsaw. It is totally doable using hand tools only, just tons more work.
    – Graphus
    Commented Feb 13 at 8:15

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